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unix: correctly track in-flight fds in sending process user_struct
The commit referenced in the Fixes tag incorrectly accounted the number of in-flight fds over a unix domain socket to the original opener of the file-descriptor. This allows another process to arbitrary deplete the original file-openers resource limit for the maximum of open files. Instead the sending processes and its struct cred should be credited. To do so, we add a reference counted struct user_struct pointer to the scm_fp_list and use it to account for the number of inflight unix fds. Fixes: 712f4aa ("unix: properly account for FDs passed over unix sockets") Reported-by: David Herrmann <dh.herrmann@gmail.com> Cc: David Herrmann <dh.herrmann@gmail.com> Cc: Willy Tarreau <w@1wt.eu> Cc: Linus Torvalds <torvalds@linux-foundation.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org> Signed-off-by: David S. Miller <davem@davemloft.net>
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+16
-8
lines changed

5 files changed

+16
-8
lines changed

Diff for: include/net/af_unix.h

+2-2
Original file line numberDiff line numberDiff line change
@@ -6,8 +6,8 @@
66
#include <linux/mutex.h>
77
#include <net/sock.h>
88

9-
void unix_inflight(struct file *fp);
10-
void unix_notinflight(struct file *fp);
9+
void unix_inflight(struct user_struct *user, struct file *fp);
10+
void unix_notinflight(struct user_struct *user, struct file *fp);
1111
void unix_gc(void);
1212
void wait_for_unix_gc(void);
1313
struct sock *unix_get_socket(struct file *filp);

Diff for: include/net/scm.h

+1
Original file line numberDiff line numberDiff line change
@@ -21,6 +21,7 @@ struct scm_creds {
2121
struct scm_fp_list {
2222
short count;
2323
short max;
24+
struct user_struct *user;
2425
struct file *fp[SCM_MAX_FD];
2526
};
2627

Diff for: net/core/scm.c

+7
Original file line numberDiff line numberDiff line change
@@ -87,6 +87,7 @@ static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
8787
*fplp = fpl;
8888
fpl->count = 0;
8989
fpl->max = SCM_MAX_FD;
90+
fpl->user = NULL;
9091
}
9192
fpp = &fpl->fp[fpl->count];
9293

@@ -107,6 +108,10 @@ static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
107108
*fpp++ = file;
108109
fpl->count++;
109110
}
111+
112+
if (!fpl->user)
113+
fpl->user = get_uid(current_user());
114+
110115
return num;
111116
}
112117

@@ -119,6 +124,7 @@ void __scm_destroy(struct scm_cookie *scm)
119124
scm->fp = NULL;
120125
for (i=fpl->count-1; i>=0; i--)
121126
fput(fpl->fp[i]);
127+
free_uid(fpl->user);
122128
kfree(fpl);
123129
}
124130
}
@@ -336,6 +342,7 @@ struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
336342
for (i = 0; i < fpl->count; i++)
337343
get_file(fpl->fp[i]);
338344
new_fpl->max = new_fpl->count;
345+
new_fpl->user = get_uid(fpl->user);
339346
}
340347
return new_fpl;
341348
}

Diff for: net/unix/af_unix.c

+2-2
Original file line numberDiff line numberDiff line change
@@ -1496,7 +1496,7 @@ static void unix_detach_fds(struct scm_cookie *scm, struct sk_buff *skb)
14961496
UNIXCB(skb).fp = NULL;
14971497

14981498
for (i = scm->fp->count-1; i >= 0; i--)
1499-
unix_notinflight(scm->fp->fp[i]);
1499+
unix_notinflight(scm->fp->user, scm->fp->fp[i]);
15001500
}
15011501

15021502
static void unix_destruct_scm(struct sk_buff *skb)
@@ -1561,7 +1561,7 @@ static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
15611561
return -ENOMEM;
15621562

15631563
for (i = scm->fp->count - 1; i >= 0; i--)
1564-
unix_inflight(scm->fp->fp[i]);
1564+
unix_inflight(scm->fp->user, scm->fp->fp[i]);
15651565
return max_level;
15661566
}
15671567

Diff for: net/unix/garbage.c

+4-4
Original file line numberDiff line numberDiff line change
@@ -116,7 +116,7 @@ struct sock *unix_get_socket(struct file *filp)
116116
* descriptor if it is for an AF_UNIX socket.
117117
*/
118118

119-
void unix_inflight(struct file *fp)
119+
void unix_inflight(struct user_struct *user, struct file *fp)
120120
{
121121
struct sock *s = unix_get_socket(fp);
122122

@@ -133,11 +133,11 @@ void unix_inflight(struct file *fp)
133133
}
134134
unix_tot_inflight++;
135135
}
136-
fp->f_cred->user->unix_inflight++;
136+
user->unix_inflight++;
137137
spin_unlock(&unix_gc_lock);
138138
}
139139

140-
void unix_notinflight(struct file *fp)
140+
void unix_notinflight(struct user_struct *user, struct file *fp)
141141
{
142142
struct sock *s = unix_get_socket(fp);
143143

@@ -152,7 +152,7 @@ void unix_notinflight(struct file *fp)
152152
list_del_init(&u->link);
153153
unix_tot_inflight--;
154154
}
155-
fp->f_cred->user->unix_inflight--;
155+
user->unix_inflight--;
156156
spin_unlock(&unix_gc_lock);
157157
}
158158

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