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unix: correctly track in-flight fds in sending process user_struct

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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: 712f4aad40 ("unix: properly account for FDs passed over unix sockets")
Reported-by: David Herrmann <[email protected]>
Cc: David Herrmann <[email protected]>
Cc: Willy Tarreau <[email protected]>
Cc: Linus Torvalds <[email protected]>
Suggested-by: Linus Torvalds <[email protected]>
Signed-off-by: Hannes Frederic Sowa <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Hannes Frederic Sowa 2016-02-03 02:11:03 +01:00 • committed by David S. Miller
commit 415e3d3e90
5 changed files with 16 additions and 8 deletions
Download patch file Download diff file Expand all files Collapse all files

4
net/unix/af_unix.c
View file

@ -1496,7 +1496,7 @@ static void unix_detach_fds(struct scm_cookie *scm, struct sk_buff *skb)
UNIXCB(skb).fp = NULL;
for (i = scm->fp->count-1; i >= 0; i--)
unix_notinflight(scm->fp->fp[i]);
unix_notinflight(scm->fp->user, scm->fp->fp[i]);
}
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)
return -ENOMEM;
for (i = scm->fp->count - 1; i >= 0; i--)
unix_inflight(scm->fp->fp[i]);
unix_inflight(scm->fp->user, scm->fp->fp[i]);
return max_level;
}

8
net/unix/garbage.c
View file

@ -116,7 +116,7 @@ struct sock *unix_get_socket(struct file *filp)
* descriptor if it is for an AF_UNIX socket.
*/
void unix_inflight(struct file *fp)
void unix_inflight(struct user_struct *user, struct file *fp)
{
struct sock *s = unix_get_socket(fp);
@ -133,11 +133,11 @@ void unix_inflight(struct file *fp)
}
unix_tot_inflight++;
}
fp->f_cred->user->unix_inflight++;
user->unix_inflight++;
spin_unlock(&unix_gc_lock);
}
void unix_notinflight(struct file *fp)
void unix_notinflight(struct user_struct *user, struct file *fp)
{
struct sock *s = unix_get_socket(fp);
@ -152,7 +152,7 @@ void unix_notinflight(struct file *fp)
list_del_init(&u->link);
unix_tot_inflight--;
}
fp->f_cred->user->unix_inflight--;
user->unix_inflight--;
spin_unlock(&unix_gc_lock);
}