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MFC r346602, r346670-r346671, r347183: tun/tap race fixes
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r346602:
tun(4): Defer clearing TUN_OPEN until much later

tun destruction will not continue until TUN_OPEN is cleared. There are brief
moments in tunclose where the mutex is dropped and we've already cleared
TUN_OPEN, so tun_destroy would be able to proceed while we're in the middle
of cleaning up the tun still. tun_destroy should be blocked until these
parts (address/route purges, mostly) are complete.

r346670:
tun/tap: close race between destroy/ioctl handler

It seems that there should be a better way to handle this, but this seems to
be the more common approach and it should likely get replaced in all of the
places it happens... Basically, thread 1 is in the process of destroying the
tun/tap while thread 2 is executing one of the ioctls that requires the
tun/tap mutex and the mutex is destroyed before the ioctl handler can
acquire it.

This is only one of the races described/found in PR 233955.

r346671:
tun(4): Don't allow open of open or dying devices

Previously, a pid check was used to prevent open of the tun(4); this works,
but may not make the most sense as we don't prevent the owner process from
opening the tun device multiple times.

The potential race described near tun_pid should not be an issue: if a
tun(4) is to be handed off, its fd has to have been sent via control message
or some other mechanism that duplicates the fd to the receiving process so
that it may set the pid. Otherwise, the pid gets cleared when the original
process closes it and you have no effective handoff mechanism.

Close up another potential issue with handing a tun(4) off by not clobbering
state if the closer isn't the controller anymore. If we want some state to
be cleared, we should do that a little more surgically.

Additionally, nothing prevents a dying tun(4) from being "reopened" in the
middle of tun_destroy as soon as the mutex is unlocked, quickly leading to a
bad time. Return EBUSY if we're marked for destruction, as well, and the
consumer will need to deal with it. The associated character device will be
destroyed in short order.

r347183:
geom: fix initialization order

There's a race between the initialization of devsoftc.mtx (by devinit)
and the creation of the geom worker thread g_run_events, which calls
devctl_queue_data_f. Both of those are initialized at SI_SUB_DRIVERS
and SI_ORDER_FIRST, which means the geom worked thread can be created
before the mutex has been initialized, leading to the panic below:

 wpanic: mtx_lock() of spin mutex (null) @ /usr/home/osstest/build.135317.build-amd64-freebsd/freebsd/sys/kern/subr_bus.c:620
 cpuid = 3
 time = 1
 KDB: stack backtrace:
 db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe003b968710
 vpanic() at vpanic+0x19d/frame 0xfffffe003b968760
 panic() at panic+0x43/frame 0xfffffe003b9687c0
 __mtx_lock_flags() at __mtx_lock_flags+0x145/frame 0xfffffe003b968810
 devctl_queue_data_f() at devctl_queue_data_f+0x6a/frame 0xfffffe003b968840
 g_dev_taste() at g_dev_taste+0x463/frame 0xfffffe003b968a00
 g_load_class() at g_load_class+0x1bc/frame 0xfffffe003b968a30
 g_run_events() at g_run_events+0x197/frame 0xfffffe003b968a70
 fork_exit() at fork_exit+0x84/frame 0xfffffe003b968ab0
 fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe003b968ab0
 --- trap 0, rip = 0, rsp = 0, rbp = 0 ---
 KDB: enter: panic
 [ thread pid 13 tid 100029 ]
 Stopped at      kdb_enter+0x3b: movq    $0,kdb_why

Fix this by initializing geom at SI_ORDER_SECOND instead of
SI_ORDER_FIRST.

PR:		233955
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@kevans91
kevans91 committed May 9, 2019
1 parent 86a27a0 commit e42a63a
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Showing 3 changed files with 53 additions and 20 deletions.
2 changes: 1 addition & 1 deletion sys/geom/geom.h
View file
Expand Up @@ -415,7 +415,7 @@ g_free(void *ptr)
static moduledata_t name##_mod = { \
#name, g_modevent, &class \
}; \
DECLARE_MODULE(name, name##_mod, SI_SUB_DRIVERS, SI_ORDER_FIRST);
DECLARE_MODULE(name, name##_mod, SI_SUB_DRIVERS, SI_ORDER_SECOND);

int g_is_geom_thread(struct thread *td);

Expand Down
19 changes: 18 additions & 1 deletion sys/net/if_tap.c
View file
Expand Up @@ -41,6 +41,7 @@

#include <sys/param.h>
#include <sys/conf.h>
#include <sys/lock.h>
#include <sys/fcntl.h>
#include <sys/filio.h>
#include <sys/jail.h>
Expand All @@ -55,6 +56,7 @@
#include <sys/signalvar.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/ttycom.h>
Expand Down Expand Up @@ -163,6 +165,9 @@ MALLOC_DECLARE(M_TAP);
MALLOC_DEFINE(M_TAP, CDEV_NAME, "Ethernet tunnel interface");
SYSCTL_INT(_debug, OID_AUTO, if_tap_debug, CTLFLAG_RW, &tapdebug, 0, "");

static struct sx tap_ioctl_sx;
SX_SYSINIT(tap_ioctl_sx, &tap_ioctl_sx, "tap_ioctl");

SYSCTL_DECL(_net_link);
static SYSCTL_NODE(_net_link, OID_AUTO, tap, CTLFLAG_RW, 0,
"Ethernet tunnel software network interface");
Expand Down Expand Up @@ -218,6 +223,10 @@ tap_destroy(struct tap_softc *tp)
struct ifnet *ifp = tp->tap_ifp;

CURVNET_SET(ifp->if_vnet);
sx_xlock(&tap_ioctl_sx);
ifp->if_softc = NULL;
sx_xunlock(&tap_ioctl_sx);

destroy_dev(tp->tap_dev);
seldrain(&tp->tap_rsel);
knlist_clear(&tp->tap_rsel.si_note, 0);
Expand Down Expand Up @@ -601,12 +610,18 @@ tapifinit(void *xtp)
static int
tapifioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
{
struct tap_softc *tp = ifp->if_softc;
struct tap_softc *tp;
struct ifreq *ifr = (struct ifreq *)data;
struct ifstat *ifs = NULL;
struct ifmediareq *ifmr = NULL;
int dummy, error = 0;

sx_xlock(&tap_ioctl_sx);
tp = ifp->if_softc;
if (tp == NULL) {
error = ENXIO;
goto bad;
}
switch (cmd) {
case SIOCSIFFLAGS: /* XXX -- just like vmnet does */
case SIOCADDMULTI:
Expand Down Expand Up @@ -649,6 +664,8 @@ tapifioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
break;
}

bad:
sx_xunlock(&tap_ioctl_sx);
return (error);
} /* tapifioctl */

Expand Down
52 changes: 34 additions & 18 deletions sys/net/if_tun.c
View file
Expand Up @@ -20,6 +20,7 @@
#include "opt_inet6.h"

#include <sys/param.h>
#include <sys/lock.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/systm.h>
Expand All @@ -30,6 +31,7 @@
#include <sys/fcntl.h>
#include <sys/filio.h>
#include <sys/sockio.h>
#include <sys/sx.h>
#include <sys/ttycom.h>
#include <sys/poll.h>
#include <sys/selinfo.h>
Expand Down Expand Up @@ -79,16 +81,10 @@ struct tun_softc {
#define TUN_RWAIT 0x0040
#define TUN_ASYNC 0x0080
#define TUN_IFHEAD 0x0100
#define TUN_DYING 0x0200

#define TUN_READY (TUN_OPEN | TUN_INITED)

/*
* XXXRW: tun_pid is used to exclusively lock /dev/tun. Is this
* actually needed? Can we just return EBUSY if already open?
* Problem is that this involved inherent races when a tun device
* is handed off from one process to another, as opposed to just
* being slightly stale informationally.
*/
pid_t tun_pid; /* owning pid */
struct ifnet *tun_ifp; /* the interface */
struct sigio *tun_sigio; /* information for async I/O */
Expand All @@ -115,6 +111,9 @@ static struct clonedevs *tunclones;
static TAILQ_HEAD(,tun_softc) tunhead = TAILQ_HEAD_INITIALIZER(tunhead);
SYSCTL_INT(_debug, OID_AUTO, if_tun_debug, CTLFLAG_RW, &tundebug, 0, "");

static struct sx tun_ioctl_sx;
SX_SYSINIT(tun_ioctl_sx, &tun_ioctl_sx, "tun_ioctl");

SYSCTL_DECL(_net_link);
static SYSCTL_NODE(_net_link, OID_AUTO, tun, CTLFLAG_RW, 0,
"IP tunnel software network interface.");
Expand Down Expand Up @@ -272,12 +271,17 @@ tun_destroy(struct tun_softc *tp)
struct cdev *dev;

mtx_lock(&tp->tun_mtx);
tp->tun_flags |= TUN_DYING;
if ((tp->tun_flags & TUN_OPEN) != 0)
cv_wait_unlock(&tp->tun_cv, &tp->tun_mtx);
else
mtx_unlock(&tp->tun_mtx);

CURVNET_SET(TUN2IFP(tp)->if_vnet);
sx_xlock(&tun_ioctl_sx);
TUN2IFP(tp)->if_softc = NULL;
sx_xunlock(&tun_ioctl_sx);

dev = tp->tun_dev;
bpfdetach(TUN2IFP(tp));
if_detach(TUN2IFP(tp));
Expand Down Expand Up @@ -464,19 +468,13 @@ tunopen(struct cdev *dev, int flag, int mode, struct thread *td)
tp = dev->si_drv1;
}

/*
* XXXRW: This use of tun_pid is subject to error due to the
* fact that a reference to the tunnel can live beyond the
* death of the process that created it. Can we replace this
* with a simple busy flag?
*/
mtx_lock(&tp->tun_mtx);
if (tp->tun_pid != 0 && tp->tun_pid != td->td_proc->p_pid) {
if ((tp->tun_flags & (TUN_OPEN | TUN_DYING)) != 0) {
mtx_unlock(&tp->tun_mtx);
return (EBUSY);
}
tp->tun_pid = td->td_proc->p_pid;

tp->tun_pid = td->td_proc->p_pid;
tp->tun_flags |= TUN_OPEN;
ifp = TUN2IFP(tp);
if_link_state_change(ifp, LINK_STATE_UP);
Expand All @@ -500,8 +498,16 @@ tunclose(struct cdev *dev, int foo, int bar, struct thread *td)
ifp = TUN2IFP(tp);

mtx_lock(&tp->tun_mtx);
tp->tun_flags &= ~TUN_OPEN;
tp->tun_pid = 0;
/*
* Simply close the device if this isn't the controlling process. This
* may happen if, for instance, the tunnel has been handed off to
* another process. The original controller should be able to close it
* without putting us into an inconsistent state.
*/
if (td->td_proc->p_pid != tp->tun_pid) {
mtx_unlock(&tp->tun_mtx);
return (0);
}

/*
* junk all pending output
Expand Down Expand Up @@ -540,6 +546,8 @@ tunclose(struct cdev *dev, int foo, int bar, struct thread *td)
selwakeuppri(&tp->tun_rsel, PZERO + 1);
KNOTE_LOCKED(&tp->tun_rsel.si_note, 0);
TUNDEBUG (ifp, "closed\n");
tp->tun_flags &= ~TUN_OPEN;
tp->tun_pid = 0;

cv_broadcast(&tp->tun_cv);
mtx_unlock(&tp->tun_mtx);
Expand Down Expand Up @@ -588,10 +596,16 @@ static int
tunifioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
{
struct ifreq *ifr = (struct ifreq *)data;
struct tun_softc *tp = ifp->if_softc;
struct tun_softc *tp;
struct ifstat *ifs;
int error = 0;

sx_xlock(&tun_ioctl_sx);
tp = ifp->if_softc;
if (tp == NULL) {
error = ENXIO;
goto bad;
}
switch(cmd) {
case SIOCGIFSTATUS:
ifs = (struct ifstat *)data;
Expand All @@ -618,6 +632,8 @@ tunifioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
default:
error = EINVAL;
}
bad:
sx_xunlock(&tun_ioctl_sx);
return (error);
}

Expand Down

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