syscall: Setuid/Setgid doesn't apply to all threads on Linux #1435

gopherbot · 2011-01-21T11:10:56Z

What steps will reproduce the problem?

Compile attached test code. Run it as root like this:

# GOMAXPROCS=4 ./test 65534 65534

and note output:

gorutine 1: uid=0 euid=0 gid=0 egid=0
gorutine 2: uid=0 euid=0 gid=0 egid=0
gorutine 3: uid=0 euid=0 gid=0 egid=0
gorutine 4: uid=0 euid=0 gid=0 egid=0
gorutine 5: uid=0 euid=0 gid=0 egid=0
gorutine 6: uid=0 euid=0 gid=0 egid=0
gorutine 7: uid=0 euid=0 gid=0 egid=0
gorutine 8: uid=0 euid=0 gid=0 egid=0
gorutine 9: uid=0 euid=0 gid=0 egid=0
gorutine 0: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 1: uid=0 euid=0 gid=0 egid=0
gorutine 2: uid=0 euid=0 gid=0 egid=0
gorutine 3: uid=0 euid=0 gid=0 egid=0
gorutine 4: uid=0 euid=0 gid=0 egid=0
gorutine 5: uid=0 euid=0 gid=0 egid=0
gorutine 6: uid=0 euid=0 gid=0 egid=0
gorutine 7: uid=0 euid=0 gid=0 egid=0
gorutine 8: uid=0 euid=0 gid=0 egid=0
gorutine 9: uid=0 euid=0 gid=0 egid=0
gorutine 0: uid=65534 euid=65534 gid=65534 egid=65534

Use ps -efL during test execution and note output:

UID        PID  PPID   LWP  C NLWP STIME TTY          TIME CMD
nobody   26088 25928 26088  0   10 11:56 pts/1    00:00:00 ./test 65534 65534
root     26088 25928 26089  0   10 11:56 pts/1    00:00:00 ./test 65534 65534
root     26088 25928 26090  0   10 11:56 pts/1    00:00:00 ./test 65534 65534
root     26088 25928 26091  0   10 11:56 pts/1    00:00:00 ./test 65534 65534
root     26088 25928 26092  0   10 11:56 pts/1    00:00:00 ./test 65534 65534
root     26088 25928 26093  0   10 11:56 pts/1    00:00:00 ./test 65534 65534
root     26088 25928 26094  0   10 11:56 pts/1    00:00:00 ./test 65534 65534
root     26088 25928 26095  0   10 11:56 pts/1    00:00:00 ./test 65534 65534
root     26088 25928 26096  0   10 11:56 pts/1    00:00:00 ./test 65534 65534
root     26088 25928 26097  0   10 11:56 pts/1    00:00:00 ./test 65534 65534

What is the expected output?

All threads must have the same UID/GID: (65534, nobody user in my system).

Which compiler are you using (5g, 6g, 8g, gccgo)?

I tested this with 6g and 8g.

Which operating system are you using?

Linux (Debian 6.0 SID on i386, Ubuntu 10.10 on amd64)

Which revision are you using?  (hg identify)

d8ba80011a98 release/release.2011-01-20

Please provide any additional information below.

http://groups.google.com/group/golang-nuts/browse_thread/thread/59597aafdd84a0e

Attachments:

test.go (1067 bytes)

gopherbot · 2011-01-21T13:17:59Z

Comment 1 by m@capitanio.org:

Well, you just must just put the gorutine creation after the suid/sguid call.
Isn't that what you would actually expect?
...
    en = syscall.Setuid(uid)
    if en != 0 {
        fmt.Println("Setuid error:", os.Errno(en))
        os.Exit(1)
    }
    
    for ii := 1; ii < 10; ii++ {
        go printIds(ii)
        time.Sleep(1e8)
    }
    printIds(0)
sudo -i
export GOMAXPROCS=2
/tmp/setuid 65534 65534
gorutine 1: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 2: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 3: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 4: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 5: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 6: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 7: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 8: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 9: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 0: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 1: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 2: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 3: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 4: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 5: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 6: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 7: uid=65534 euid=65534 gid=65534 egid=65534
gorutine 8: uid=65534 euid=65534 gid=65534 egid=65534

alberts · 2011-01-21T13:22:34Z

Comment 2:

By the time main starts executing it might be too late to be sure that you cover all the
goroutines.
A package could do:
func init() {
    go someHousekeepingFunc()
}
which would then have the wrong uid/gid.

alberts · 2011-01-21T13:25:27Z

Comment 3:

A more concrete example of this is perhaps:
http://golang.org/src/pkg/time/tick.go
To be safe, one would have to check the code of every package you import to be sure that
you don't inadvertently call a function that starts a goroutine before you get round to
calling Setuid.

gopherbot · 2011-01-21T14:04:24Z

Comment 4 by m@capitanio.org:

You could use runtime.Goroutines() to wait if you are the only one.
If it isn't possible to terminate all "someHousekeepingFunc()" e.g.
with Goexit(), I think setuid gains you to security not much ...

gopherbot · 2011-01-21T17:57:29Z

Comment 5 by ziutek@Lnet.pl:

Example code which shows how I discovered this problem:
package main
import (
    "os"
    "net"
    "http"
    "fmt"
    "syscall"
    "log"
)
type Handler string
func (hh *Handler) ServeHTTP(con http.ResponseWriter, req *http.Request) {
    fmt.Fprint(con, "Hello! I am %s. My UID/GID is %d/%d. Bye!\n", *hh,
        syscall.Getuid(), syscall.Getgid())
}
func main() {
    // To listen on port 80 we need root privileges
    ls, err := net.Listen("tcp", "127.0.0.1:80")
    if err != nil {
        log.Exitln("Can't listen:", err)
    }
    // We don't need root privileges any more
    if en := syscall.Setgid(65534); en != 0 {
        log.Exitln("Setgid error:", os.Errno(en))
    }
    if en := syscall.Setuid(65534); en != 0 {
        log.Exitln("Setuid error:", os.Errno(en))
    }
    // Run http service without root privileges
    handler := Handler("Test handler")
    if err = http.Serve(ls, &handler); err != nil {
        log.Exitln("Http server:", err)
    }
}
Compile it and run as root. Then use ps -efL to show threads:
UID        PID  PPID   LWP  C NLWP STIME TTY          TIME CMD
nobody   32401 32333 32401  0    2 18:48 pts/2    00:00:00 ./http
root     32401 32333 32402  0    2 18:48 pts/2    00:00:00 ./http
There is two threads. But I didn't create any gorutine explicitly. Use curl to send
request to the application:
$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 65534/65534. Bye!
Now ps shows:
UID        PID  PPID   LWP  C NLWP STIME TTY          TIME CMD
nobody   32401 32333 32401  0    3 18:48 pts/2    00:00:00 ./http
root     32401 32333 32402  0    3 18:48 pts/2    00:00:00 ./http
nobody   32401 32333 32406  0    3 18:49 pts/2    00:00:00 ./http
Use siege stress test:
$ siege 127.0.0.1 -c25 -d0 -t 10s
** SIEGE 2.70
** Preparing 25 concurrent users for battle.
The server is now under siege...
Lifting the server siege..      done.                                                   
 Transactions:             12543 hits
Availability:             100.00 %
Elapsed time:               9.99 secs
Data transferred:           0.65 MB
Response time:              0.02 secs
Transaction rate:        1255.56 trans/sec
Throughput:             0.06 MB/sec
Concurrency:               24.79
Successful transactions:       12544
Failed transactions:               0
Longest transaction:            0.04
Shortest transaction:           0.01
 
Now ps shows:
UID        PID  PPID   LWP  C NLWP STIME TTY          TIME CMD
nobody   32401 32333 32401  0   11 18:48 pts/2    00:00:01 ./http
root     32401 32333 32402  0   11 18:48 pts/2    00:00:01 ./http
nobody   32401 32333 32406  0   11 18:49 pts/2    00:00:01 ./http
nobody   32401 32333 32553  0   11 18:51 pts/2    00:00:00 ./http
nobody   32401 32333 32554  2   11 18:51 pts/2    00:00:01 ./http
root     32401 32333 32555  3   11 18:51 pts/2    00:00:01 ./http
root     32401 32333 32556  3   11 18:51 pts/2    00:00:01 ./http
root     32401 32333 32557  0   11 18:51 pts/2    00:00:00 ./http
root     32401 32333 32558  3   11 18:51 pts/2    00:00:01 ./http
nobody   32401 32333 32559  3   11 18:51 pts/2    00:00:01 ./http
nobody   32401 32333 32560  3   11 18:51 pts/2    00:00:01 ./http
Use curl a few times:
$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 0/0. Bye!
$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 0/0. Bye!
$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 0/0. Bye!
It's nice! I talking with root on your server!

gopherbot · 2011-01-21T19:01:23Z

Comment 6 by m@capitanio.org:

Oh, you are right. There is currently no official way to use a net socket without
spawning 2nd goroutine (EpollWait):
goroutine 2 [3]:
runtime.entersyscall+0x28 /data4/soft/go/go/src/pkg/runtime/proc.c:577
    runtime.entersyscall()
syscall.Syscall6+0x5 /data4/soft/go/go/src/pkg/syscall/asm_linux_amd64.s:40
    syscall.Syscall6()
syscall.EpollWait+0x8d /data4/soft/go/go/src/pkg/syscall/zsyscall_linux_amd64.go:188
    syscall.EpollWait(0x7fda00000006, 0x7fda62d566a0, 0x100000001, 0xffffffff, 0xc, ...)
net.*pollster·WaitFD+0xfe /data4/soft/go/go/src/pkg/net/fd_linux.go:116
    net.*pollster·WaitFD(0x7fda62d564d0, 0x0, 0x0, 0x0, 0x0, ...)
net.*pollServer·Run+0xa3 /data4/soft/go/go/src/pkg/net/fd.go:207
    net.*pollServer·Run(0x7fda62d20600, 0x0)
runtime.goexit /data4/soft/go/go/src/pkg/runtime/proc.c:149
    runtime.goexit()
but opening a file descriptor works:
f, err := os.Open("/etc/shadow", os.O_RDONLY | os.O_SYNC , 0666)
fmt.Println(runtime.Goroutines())
... syscall.Setuid(uid) ... syscall.Setgid(gid)
var buf [20]byte
_, err = f.Read(buf[:]);
fmt.Println(buf)
time.Sleep(100e9)
./run
open /etc/shadow: permission denied
sudo ./run
1
[114 111 111 ...
ps -efL|grep run
mc       14097 24745 14097  0    1 19:36 pts/4    00:00:00 /run 1001 1001

robpike · 2011-01-21T20:13:31Z

Comment 7:

Owner changed to r...@golang.org.

Status changed to Accepted.

rsc · 2011-01-21T20:57:25Z

Comment 8:

The syscall is doing what it advertises: it invokes
the Linux system call.  And the Linux system call only
affects the calling thread (!), confirmed by reading the
sources.
I was surprised to find that setuid works when called
from a C Linux pthreads (NPTL) program, though.
So I investigated further.
It turns out that glibc's setuid sends a signal to every
other thread to cause them to invoke the system call too.
http://goo.gl/8zf3C - called by setuid
http://goo.gl/CcXyX - signal handler
I suppose Go is going to need to do this at some point,
as part of implementing os.Setuid, os.Setgid, etc.
What a crock.
For now you can work around this by calling runtime.LockOSThread.
That locks the goroutine onto its current OS thread, so that
it only runs in that thread and that thread only runs that goroutine.
Then you can call Setuid Setgid etc and also ForkExec.

Status changed to LongTerm.

gopherbot · 2011-01-21T21:38:49Z

Comment 9 by ziutek@Lnet.pl:

If I add runtime.LockOSThread in my second example, just before Setgid, I get strange
behavior:
michal@md-lap:~$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 65534/0. Bye!
michal@md-lap:~$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 0/65534. Bye!
michal@md-lap:~$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 0/0. Bye!
michal@md-lap:~$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 65534/65534. Bye!
michal@md-lap:~$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 65534/65534. Bye!
michal@md-lap:~$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 65534/0. Bye!
michal@md-lap:~$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 65534/65534. Bye!
michal@md-lap:~$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 0/0. Bye!
michal@md-lap:~$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 65534/65534. Bye!
michal@md-lap:~$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 0/0. Bye!
michal@md-lap:~$ curl 127.0.0.1
Hello! I am Test handler. My UID/GID is 0/65534. Bye!

Attachments:

http.go (969 bytes)

gopherbot · 2011-01-21T21:45:14Z

Comment 10 by ziutek@Lnet.pl:

Sorry. I had not noticed it before, but this is also when there is no
runtime.LockOSThread call.
This is probably due to rescheduling between syscall.Getuid() and syscall.Getgid().

rsc · 2011-01-21T22:04:24Z

Comment 11:

Yes, even with LockOSThread it only applies to the current goroutine.
If you check from another goroutine, you may or may not see the change.
Sorry.
Another possible workaround for your specific case is to use setcap(8)
to give the binary the CAP_NET_BIND_SERVICE capability only.

gopherbot · 2011-01-21T22:07:19Z

Comment 12 by ziutek@Lnet.pl:

I probably found workaround for my web application:
package main
import (
    "os"
    "net"
    "http"
    "fmt"
    "syscall"
    "runtime"
    "log"
)
func lockUidGid(new_uid, new_gid int) {
    runtime.LockOSThread()
    uid := syscall.Getuid()
    gid := syscall.Getgid()
    if  uid == new_uid && gid == new_gid {
        return
    }
    if en := syscall.Setgid(new_uid); en != 0 {
        log.Exitln("Setgid error:", os.Errno(en))
    }
    if en := syscall.Setuid(new_gid); en != 0 {
        log.Exitln("Setuid error:", os.Errno(en))
    }
}
type Handler string
func (hh *Handler) ServeHTTP(con http.ResponseWriter, req *http.Request) {
    lockUidGid(65534, 65534)
    fmt.Fprintf(con, "Hello! I am %s. My UID/GID is %d/%d. Bye!\n", *hh,
        syscall.Getuid(), syscall.Getgid())
}
func main() {
    // To listen on port 80 we need root privileges
    ls, err := net.Listen("tcp", "127.0.0.1:80")
    if err != nil {
        log.Exitln("Can't listen:", err)
    }
    // We don't need root privileges any more
    lockUidGid(65534, 65534)
    // Run http service without root privileges
    handler := Handler("Test handler")
    if err = http.Serve(ls, &handler); err != nil {
        log.Exitln("Http server:", err)
    }
}
After running siege there is no threads with root privileges:
$ siege 127.0.0.1 -c25 -d0 -t10s
** SIEGE 2.69
** Preparing 25 concurrent users for battle.
The server is now under siege...
Lifting the server siege..      done.
Transactions:              28782 hits
Availability:             100.00 %
Elapsed time:               9.79 secs
Data transferred:           1.59 MB
Response time:              0.01 secs
Transaction rate:        2939.94 trans/sec
Throughput:             0.16 MB/sec
Concurrency:               24.86
Successful transactions:       28782
Failed transactions:               0
Longest transaction:            0.04
Shortest transaction:           0.00
$ ps -efL|egrep 'http|UID'|egrep -v egrep
UID        PID  PPID   LWP  C NLWP STIME TTY          TIME CMD
nobody    4109  2928  4109  1   10 23:00 pts/1    00:00:04 ./http
nobody    4109  2928  4110  0   10 23:00 pts/1    00:00:02 ./http
nobody    4109  2928  4112  0   10 23:00 pts/1    00:00:02 ./http
nobody    4109  2928  4153  0   10 23:01 pts/1    00:00:01 ./http
nobody    4109  2928  4154  0   10 23:01 pts/1    00:00:00 ./http
nobody    4109  2928  4155  0   10 23:01 pts/1    00:00:00 ./http
nobody    4109  2928  4156  0   10 23:01 pts/1    00:00:01 ./http
nobody    4109  2928  4157  0   10 23:01 pts/1    00:00:00 ./http
nobody    4109  2928  4158  0   10 23:01 pts/1    00:00:01 ./http
nobody    4109  2928  4159  0   10 23:01 pts/1    00:00:01 ./http
nobody    4109  2928  4109  1   10 23:00 pts/1    00:00:04 ./http
nobody    4109  2928  4110  0   10 23:00 pts/1    00:00:02 ./http
nobody    4109  2928  4112  0   10 23:00 pts/1    00:00:02 ./http
nobody    4109  2928  4153  0   10 23:01 pts/1    00:00:01 ./http
nobody    4109  2928  4154  0   10 23:01 pts/1    00:00:00 ./http
nobody    4109  2928  4155  0   10 23:01 pts/1    00:00:00 ./http
nobody    4109  2928  4156  0   10 23:01 pts/1    00:00:01 ./http
nobody    4109  2928  4157  0   10 23:01 pts/1    00:00:00 ./http
nobody    4109  2928  4158  0   10 23:01 pts/1    00:00:01 ./http
nobody    4109  2928  4159  0   10 23:01 pts/1    00:00:01 ./http
Thanks!

gopherbot · 2011-01-21T22:10:21Z

Comment 13 by ziutek@Lnet.pl:

I probably found workaround for my web application:
package main
import (
    "os"
    "net"
    "http"
    "fmt"
    "syscall"
    "runtime"
    "log"
)
func lockUidGid(new_uid, new_gid int) {
    runtime.LockOSThread()
    uid := syscall.Getuid()
    gid := syscall.Getgid()
    if  uid == new_uid && gid == new_gid {
        return
    }
    if en := syscall.Setgid(new_uid); en != 0 {
        log.Exitln("Setgid error:", os.Errno(en))
    }
    if en := syscall.Setuid(new_gid); en != 0 {
        log.Exitln("Setuid error:", os.Errno(en))
    }
}
type Handler string
func (hh *Handler) ServeHTTP(con http.ResponseWriter, req *http.Request) {
    lockUidGid(65534, 65534)
    fmt.Fprintf(con, "Hello! I am %s. My UID/GID is %d/%d. Bye!\n", *hh,
        syscall.Getuid(), syscall.Getgid())
}
func main() {
    // To listen on port 80 we need root privileges
    ls, err := net.Listen("tcp", "127.0.0.1:80")
    if err != nil {
        log.Exitln("Can't listen:", err)
    }
    // We don't need root privileges any more
    lockUidGid(65534, 65534)
    // Run http service without root privileges
    handler := Handler("Test handler")
    if err = http.Serve(ls, &handler); err != nil {
        log.Exitln("Http server:", err)
    }
}
After running siege there is no threads with root privileges:
$ siege 127.0.0.1 -c25 -d0 -t10s
** SIEGE 2.69
** Preparing 25 concurrent users for battle.
The server is now under siege...
Lifting the server siege..      done.
Transactions:                  28782 hits
Availability:                 100.00 %
Elapsed time:                   9.79 secs
Data transferred:               1.59 MB
Response time:                  0.01 secs
Transaction rate:            2939.94 trans/sec
Throughput:                     0.16 MB/sec
Concurrency:                   24.86
Successful transactions:       28782
Failed transactions:               0
Longest transaction:            0.04
Shortest transaction:           0.00
$ ps -efL|egrep 'http|UID'|egrep -v egrep
UID        PID  PPID   LWP  C NLWP STIME TTY          TIME CMD
nobody    4109  2928  4109  1   10 23:00 pts/1    00:00:04 ./http
nobody    4109  2928  4110  0   10 23:00 pts/1    00:00:02 ./http
nobody    4109  2928  4112  0   10 23:00 pts/1    00:00:02 ./http
nobody    4109  2928  4153  0   10 23:01 pts/1    00:00:01 ./http
nobody    4109  2928  4154  0   10 23:01 pts/1    00:00:00 ./http
nobody    4109  2928  4155  0   10 23:01 pts/1    00:00:00 ./http
nobody    4109  2928  4156  0   10 23:01 pts/1    00:00:01 ./http
nobody    4109  2928  4157  0   10 23:01 pts/1    00:00:00 ./http
nobody    4109  2928  4158  0   10 23:01 pts/1    00:00:01 ./http
nobody    4109  2928  4159  0   10 23:01 pts/1    00:00:01 ./http
Thanks!

rsc · 2011-01-21T22:11:23Z

Comment 14:

It's still not guaranteed that future goroutines won't have
the original 0/0 uid/gid.  Obviously if all tasks have been
switched then you're safe but there's no guarantee that
will switch all the tasks.  Using the network capability is
much safer if you are worried about this kind of thing.
Russ

gopherbot · 2011-01-21T22:11:48Z

Comment 15 by m@capitanio.org:

>For now you can work around this by calling runtime.LockOSThread.
runtime.GOMAXPROCS(1)
runtime.LockOSThread()
ls, _ := net.Listen("tcp", "localhost:42")
syscall.Setuid(uid)
http.Serve(ls, nil)
Was that what you meant? It's actually impossible ;)
There is always +1 thread spawned by Listen that keeps
running as root.
ps -efL| grep setuid
mc       19213 24745 19213  0    2 22:41 pts/4    00:00:00 /tmp/setuid 1001 1001
root     19213 24745 19215  0    2 22:41 pts/4    00:00:00 /tmp/setuid 1001 1001
^\SIGQUIT: quit
PC=0x411b25
runtime.futex+0x23 /data4/soft/go/go/src/pkg/runtime/linux/amd64/sys.s:137
    runtime.futex()
futexsleep+0x50 /data4/soft/go/go/src/pkg/runtime/linux/thread.c:51
    futexsleep(0x664c18, 0x300000003, 0x0, 0x0)
futexlock+0x85 /data4/soft/go/go/src/pkg/runtime/linux/thread.c:119
    futexlock(0x664c18, 0x100000000)
runtime.notesleep+0x25 /data4/soft/go/go/src/pkg/runtime/linux/thread.c:204
    runtime.notesleep(0x664c18, 0x7fffa0812498)
nextgandunlock+0x146 /data4/soft/go/go/src/pkg/runtime/proc.c:343
    nextgandunlock()
scheduler+0x16f /data4/soft/go/go/src/pkg/runtime/proc.c:536
    scheduler()
runtime.mstart+0x74 /data4/soft/go/go/src/pkg/runtime/proc.c:393
    runtime.mstart()
_rt0_amd64+0x95 /data4/soft/go/go/src/pkg/runtime/amd64/asm.s:69
    _rt0_amd64()
goroutine 2 [3]:
runtime.entersyscall+0x28 /data4/soft/go/go/src/pkg/runtime/proc.c:577
    runtime.entersyscall()
syscall.Syscall6+0x5 /data4/soft/go/go/src/pkg/syscall/asm_linux_amd64.s:40
    syscall.Syscall6()
syscall.EpollWait+0x8d /data4/soft/go/go/src/pkg/syscall/zsyscall_linux_amd64.go:188
    syscall.EpollWait(0x7f6600000006, 0x7f669eb58950, 0x100000001, 0xffffffff, 0xc, ...)
net.*pollster·WaitFD+0xfe /data4/soft/go/go/src/pkg/net/fd_linux.go:116
    net.*pollster·WaitFD(0x7f669eb587a0, 0x0, 0x6400000000, 0x0, 0x0, ...)
net.*pollServer·Run+0xa3 /data4/soft/go/go/src/pkg/net/fd.go:207
    net.*pollServer·Run(0x7f669eb27600, 0x0)
runtime.goexit /data4/soft/go/go/src/pkg/runtime/proc.c:149
    runtime.goexit()
goroutine 1 [4]:
runtime.gosched+0x77 /data4/soft/go/go/src/pkg/runtime/proc.c:558
    runtime.gosched()
runtime.chanrecv+0x18b /data4/soft/go/go/src/pkg/runtime/chan.c:364
    runtime.chanrecv(0x7f669eb3eea0, 0x7f669eb13da8, 0x0, 0x0, 0x0, ...)
runtime.chanrecv1+0x41 /data4/soft/go/go/src/pkg/runtime/chan.c:444
    runtime.chanrecv1(0x7f669eb3eea0, 0x7f669eb123c0)
net.*pollServer·WaitRead+0x52 /data4/soft/go/go/src/pkg/net/fd.go:247
    net.*pollServer·WaitRead(0x7f669eb27600, 0x7f669eb123c0, 0x0, 0x0)
net.*netFD·accept+0x39a /data4/soft/go/go/src/pkg/net/fd.go:579
    net.*netFD·accept(0x7f669eb123c0, 0x43efe8, 0x0, 0x0, 0x0, ...)
net.*TCPListener·AcceptTCP+0x71 /data4/soft/go/go/src/pkg/net/tcpsock.go:261
    net.*TCPListener·AcceptTCP(0x7f669eb0f178, 0x7f669eb13ee0, 0x0, 0x0, 0x1007f6600000001, ...)
net.*TCPListener·Accept+0x49 /data4/soft/go/go/src/pkg/net/tcpsock.go:271
    net.*TCPListener·Accept(0x7f669eb0f178, 0x0, 0x0, 0x0, 0x0, ...)
http.Serve+0x7a /data4/soft/go/go/src/pkg/http/server.go:665
    http.Serve(0x7f669eb27b40, 0x7f669eb0f178, 0x7f669eb4b030, 0x7f669eb0f0a8, 0x0, ...)
main.main+0x886 /home/mc/server/go/tests/setuid2.go:73
    main.main()
runtime.mainstart+0xf /data4/soft/go/go/src/pkg/runtime/amd64/asm.s:77
    runtime.mainstart()
runtime.goexit /data4/soft/go/go/src/pkg/runtime/proc.c:149
    runtime.goexit()
rax     0xfffffffffffffffc
rbx     0x664c18
rcx     0xffffffffffffffff
rdx     0x3
rdi     0x664c18
rsi     0x0
rbp     0x7f669eb13c98
rsp     0x7fffa08123e8
r8      0x0
r9      0x0
r10     0x6601b0
r11     0x206
r12     0x250
r13     0x7fffa0812500
r14     0x0
r15     0x0
rip     0x411b25
rflags  0x206
cs      0x33
fs      0x0
gs      0x0
Trace/breakpoint trap

rsc · 2011-01-21T22:19:59Z

Comment 16:

Yes, the LockOSThread workaround only applies to one goroutine.

gopherbot · 2011-01-22T04:02:38Z

Comment 17 by m@capitanio.org:

Thanks, I didn't hit the reload button and missed the comments.
BTW, the crock design is elaborated here ;)
http://www.cs.utexas.edu/~witchel/372/lectures/POSIX_Linux_Threading.pdf

gopherbot · 2011-01-22T12:32:36Z

Comment 18 by ziutek@Lnet.pl:

I suggest put a clear warning in the header of syscall package about issues that may
cause the use of this package.
Maybe a list of links to known issues for each function would not be a bad idea...

rsc · 2011-01-22T14:55:26Z

Comment 19:

The syscall package is not for general use.
It has no documentation.  That's not going
to change.  When we have a working Setuid etc
they will be made available as part of package os.
Russ

alberts · 2011-03-30T04:53:37Z

Comment 20:

Revision a25343ee3016 has added a way of doing Setuid and Setgid as part of
StartProcess, which might help some people.

rsc · 2011-12-09T19:47:43Z

Comment 21:

Labels changed: added priority-later.

gopherbot · 2012-05-11T15:35:59Z

Comment 23 by tsar@cosmocode.de:

Is anyone working on that? If there are some experimental patches I would be happy to
test them ;-)
I added a little test case to my own little library to detect non-posix compliant
systems (all the *bsd variants work as expected): https://github.com/sarnowski/mitigation

rsc · 2012-05-15T14:54:59Z

Comment 24:

No one is working on this as far as I know.
Russ

rsc · 2012-09-12T21:41:15Z

Comment 25:

Labels changed: added go1.1.

bpowers · 2012-10-09T21:05:32Z

Comment 26:

I'm looking into this, I have a start to the implementation of what rsc suggested above.
 I've updated the example for go1, along with using the os.Setuid/os.Setgid (an API
change) from my soon-to-be-posted CL.

Attachments:

main.go (859 bytes)

rsc · 2012-12-10T04:02:51Z

Comment 27:

Labels changed: added size-l.

extemporalgenome · 2012-12-11T16:24:30Z

Comment 28:

The cause of this problem seems closely related to the cause of daemonization problems;
that is, the inability to consistently execute package main code on a vanilla runtime
before any thread spawning occurs (as was trivial with the old init behavior), or
alternatively, the ability to command the runtime to suspend goroutines at their next
non-externally-blocked scheduling point, closing all but one thread (if the runtime can
even temporarily coexist with app code in the main thread). Preemptive scheduling would
certainly make the latter simpler.

rsc · 2013-03-12T01:06:09Z

Comment 29:

We didn't get to this in time. Going to have to wait for Go 1.2 (or maybe someone will
fix the Linux kernel!).

Labels changed: added go1.2, removed go1.1.

rsc · 2013-07-30T17:13:43Z

Comment 30:

Labels changed: added go1.3maybe, removed go1.2.

robpike · 2013-08-20T23:35:45Z

Comment 31:

Labels changed: removed go1.3maybe.

AndrewGMorgan · 2021-07-31T15:10:28Z

Yes. I've also authored a native Go package for manipulating capabilities at runtime: "kernel.org/pub/linux/libs/security/libcap/cap". This worked example covers how to read/modify/drop runtime capabilities as well as manipulate UIDs etc.

lordspace · 2021-07-31T19:27:30Z

@AndrewGMorgan thanks for sharing.

The program web.go uses "libcap/cap" to raise and lower capabilities in order to bind to a privileged port. Writing this code, I now realize that Go's runtime is not really suited to minimal privilege guarantees. The code does raise and lower the effective capability Value needed, but to be fully robust, we're going to have to wait for the following issue with the Go runtime to find a resolution: golang/go#1435 Signed-off-by: Andrew G. Morgan <morgan@kernel.org>

I've moved my go.patch to address: golang/go#1435 into a development patch against the upstream Go sources: https://go-review.googlesource.com/c/go/+/210639/ and the review process will likely evolve it somewhat. I plan to ensure that working libcap/cap Go package is in sync with the working state of the above development change. As such, there is no need to keep the patch here any more. I'll keep the tests for now, as it isn't clear to me how the Go source tree supports tests that require privilege yet. Signed-off-by: Andrew G. Morgan <morgan@kernel.org>

This is something pretty fundamental that a number of folk have asked about. It is essentially the motivating issue for: golang/go#1435 Signed-off-by: Andrew G. Morgan <morgan@kernel.org>

On FreeBSD, changing a process's supplementary groups with setgroups(2) will also change the egid of the process, setting it to the first entry in the provided list. This is distinct from the behaviour on other platforms (and possibly a violation of the POSIX standard). Because of this, our incubator code wouldn't change the process's gid, because it would read the newly-changed egid, compare it against the expected egid, and since they matched, not change the gid. Fix this by ensuring that the setGroups call behaves the same on FreeBSD as it does on other platforms by adding the current egid as the first entry in the list, and thus not changing it unexpectedly. Also, while we're here... defensively call runtime.LockOSThread to make it less likely we trip over bugs like golang/go#1435 Signed-off-by: Andrew Dunham <andrew@du.nham.ca> Change-Id: Icc08c629ddc87923aa9ae0d542f63925e9c40cd3

On FreeBSD, changing a process's supplementary groups with setgroups(2) will also change the egid of the process, setting it to the first entry in the provided list. This is distinct from the behaviour on other platforms (and possibly a violation of the POSIX standard). Because of this, our incubator code wouldn't change the process's gid, because it would read the newly-changed egid, compare it against the expected egid, and since they matched, not change the gid. This could be observed by running "id -p" in two contexts. The expected output, and the output returned when running from a SSH shell, is: andrew@freebsd:~ $ id -p uid andrew groups andrew However, when run via "ssh andrew@freebsd id -p", the output would be: $ ssh andrew@freebsd id -p login root uid andrew rgid wheel groups andrew (this could also be observed via "id -g -r" to print just the gid) We fix this by ensuring that the setGroups call behaves the same on FreeBSD as it does on other platforms by adding the current egid as the first entry in the list, and thus not changing it unexpectedly. Also, while we're here... defensively call runtime.LockOSThread to make it less likely we trip over bugs like golang/go#1435 Signed-off-by: Andrew Dunham <andrew@du.nham.ca> Change-Id: Icc08c629ddc87923aa9ae0d542f63925e9c40cd3

On FreeBSD, changing a process's supplementary groups with setgroups(2) will also change the egid of the process, setting it to the first entry in the provided list. This is distinct from the behaviour on other platforms (and possibly a violation of the POSIX standard). Because of this, our incubator code wouldn't change the process's gid, because it would read the newly-changed egid, compare it against the expected egid, and since they matched, not change the gid. This could be observed by running "id -p" in two contexts. The expected output, and the output returned when running from a SSH shell, is: andrew@freebsd:~ $ id -p uid andrew groups andrew However, when run via "ssh andrew@freebsd id -p", the output would be: $ ssh andrew@freebsd id -p login root uid andrew rgid wheel groups andrew (this could also be observed via "id -g -r" to print just the gid) We fix this by ensuring that the setGroups call behaves the same on FreeBSD as it does on other platforms by adding the current egid as the first entry in the list, and thus not changing it unexpectedly. More information can be found in the following article: https://www.usenix.org/system/files/login/articles/325-tsafrir.pdf Also, while we're here... defensively call runtime.LockOSThread to make it less likely we trip over bugs like golang/go#1435 Signed-off-by: Andrew Dunham <andrew@du.nham.ca> Change-Id: Icc08c629ddc87923aa9ae0d542f63925e9c40cd3

On FreeBSD and Darwin, changing a process's supplementary groups with setgroups(2) will also change the egid of the process, setting it to the first entry in the provided list. This is distinct from the behaviour on other platforms (and possibly a violation of the POSIX standard). Because of this, our incubator code wouldn't change the process's gid, because it would read the newly-changed egid, compare it against the expected egid, and since they matched, not change the gid. This could be observed by running "id -p" in two contexts. The expected output, and the output returned when running from a SSH shell, is: andrew@freebsd:~ $ id -p uid andrew groups andrew However, when run via "ssh andrew@freebsd id -p", the output would be: $ ssh andrew@freebsd id -p login root uid andrew rgid wheel groups andrew (this could also be observed via "id -g -r" to print just the gid) We fix this by ensuring that the setGroups call behaves the same on FreeBSD as it does on other platforms by adding the current egid as the first entry in the list, and thus not changing it unexpectedly. More information can be found in the following article: https://www.usenix.org/system/files/login/articles/325-tsafrir.pdf Also, while we're here... defensively call runtime.LockOSThread to make it less likely we trip over bugs like golang/go#1435 Signed-off-by: Andrew Dunham <andrew@du.nham.ca> Change-Id: Icc08c629ddc87923aa9ae0d542f63925e9c40cd3

wxiaoguang · 2023-03-22T10:17:07Z

The Milestone is "unplanned`, I guess it should be "1.16"?

ianlancetaylor · 2023-03-22T18:59:35Z

Sorry, we don't try to set the milestone when we close an issue. But, yes, this was fixed in the 1.16 release.

This makes it less likely that we trip over bugs like golang/go#1435. Updates #7616 Signed-off-by: Andrew Dunham <andrew@du.nham.ca> Change-Id: Ic28c03c3ad8ed5274a795c766b767fa876029f0e

This makes it less likely that we trip over bugs like golang/go#1435. Updates tailscale#7616 Signed-off-by: Andrew Dunham <andrew@du.nham.ca> Change-Id: Ic28c03c3ad8ed5274a795c766b767fa876029f0e

Since Go 1.16, [Go issue 1435][1] is solved, and the stdlib syscall implementations work on Linux. While they are a bit more flexible/heavier-weight than the implementations that were copied to libcontainer/system (working across all threads), we compile with Cgo, and using the libc wrappers should be just as suitable. [1]: golang/go#1435 Signed-off-by: Bjorn Neergaard <bjorn.neergaard@docker.com>

Since Go 1.16, [Go issue 1435][1] is solved, and the stdlib syscall implementations work on Linux. [1]: golang/go#1435 Signed-off-by: Bjorn Neergaard <bjorn.neergaard@docker.com>

mrusme mentioned this issue May 6, 2022

Implement syscall.Setgid/syscall.Setuid charmbracelet/soft-serve#116

Closed

rafaeldtinoco mentioned this issue Jun 8, 2022

[BUG] intermittent errors after PR 1202 (drop privileges) aquasecurity/tracee#1803

Closed

5 tasks

rsc unassigned AndrewGMorgan Jun 22, 2022

NicolasT mentioned this issue Aug 20, 2022

Document issue with multiple threads NicolasT/landlock-hs#9

Closed

dgryski mentioned this issue Nov 7, 2022

Setuid not declared by package syscall tinygo-org/tinygo#3274

Closed

andrew-d mentioned this issue Mar 19, 2023

ssh/tailssh: fix privilege dropping on FreeBSD tailscale/tailscale#7609

Closed

andrew-d mentioned this issue Mar 23, 2023

ssh/tailssh: lock OS thread during incubator tailscale/tailscale#7660

Merged

neersighted mentioned this issue Oct 11, 2023

libcontainer: drop system.Setxid opencontainers/runc#4067

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syscall: Setuid/Setgid doesn't apply to all threads on Linux #1435

syscall: Setuid/Setgid doesn't apply to all threads on Linux #1435

gopherbot commented Jan 21, 2011

gopherbot commented Jan 21, 2011

alberts commented Jan 21, 2011

alberts commented Jan 21, 2011

gopherbot commented Jan 21, 2011

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robpike commented Jan 21, 2011

rsc commented Jan 21, 2011

gopherbot commented Jan 21, 2011

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rsc commented Jan 21, 2011

gopherbot commented Jan 21, 2011

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rsc commented Jan 21, 2011

gopherbot commented Jan 21, 2011

rsc commented Jan 21, 2011

gopherbot commented Jan 22, 2011

gopherbot commented Jan 22, 2011

rsc commented Jan 22, 2011

alberts commented Mar 30, 2011

rsc commented Dec 9, 2011

gopherbot commented May 11, 2012

rsc commented May 15, 2012

rsc commented Sep 12, 2012

bpowers commented Oct 9, 2012

rsc commented Dec 10, 2012

extemporalgenome commented Dec 11, 2012

rsc commented Mar 12, 2013

rsc commented Jul 30, 2013

robpike commented Aug 20, 2013

AndrewGMorgan commented Jul 31, 2021

lordspace commented Jul 31, 2021

wxiaoguang commented Mar 22, 2023

ianlancetaylor commented Mar 22, 2023

syscall: Setuid/Setgid doesn't apply to all threads on Linux #1435

syscall: Setuid/Setgid doesn't apply to all threads on Linux #1435

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rsc commented Dec 10, 2012

extemporalgenome commented Dec 11, 2012

rsc commented Mar 12, 2013

rsc commented Jul 30, 2013

robpike commented Aug 20, 2013

AndrewGMorgan commented Jul 31, 2021

lordspace commented Jul 31, 2021

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ianlancetaylor commented Mar 22, 2023