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net: unix: fix inflight counting bug in garbage collector

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Previously I assumed that the receive queues of candidates don't
change during the GC.  This is only half true, nothing can be received
from the queues (see comment in unix_gc()), but buffers could be added
through the other half of the socket pair, which may still have file
descriptors referring to it.

This can result in inc_inflight_move_tail() erronously increasing the
"inflight" counter for a unix socket for which dec_inflight() wasn't
previously called.  This in turn can trigger the "BUG_ON(total_refs <
inflight_refs)" in a later garbage collection run.

Fix this by only manipulating the "inflight" counter for sockets which
are candidates themselves.  Duplicating the file references in
unix_attach_fds() is also needed to prevent a socket becoming a
candidate for GC while the skb that contains it is not yet queued.

Reported-by: Andrea Bittau <a.bittau@cs.ucl.ac.uk>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
CC: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Miklos Szeredi 2008-11-09 15:23:57 +01:00 • committed by Linus Torvalds
parent 058e3739f6
commit 6209344f5a
3 changed files with 62 additions and 19 deletions
Download patch file Download diff file Expand all files Collapse all files

31
net/unix/af_unix.c
View file

@ -1302,14 +1302,23 @@ static void unix_destruct_fds(struct sk_buff *skb)
sock_wfree(skb);
}
static void unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
static int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
{
int i;
/*
* Need to duplicate file references for the sake of garbage
* collection. Otherwise a socket in the fps might become a
* candidate for GC while the skb is not yet queued.
*/
UNIXCB(skb).fp = scm_fp_dup(scm->fp);
if (!UNIXCB(skb).fp)
return -ENOMEM;
for (i=scm->fp->count-1; i>=0; i--)
unix_inflight(scm->fp->fp[i]);
UNIXCB(skb).fp = scm->fp;
skb->destructor = unix_destruct_fds;
scm->fp = NULL;
return 0;
}
/*
@ -1368,8 +1377,11 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
goto out;
memcpy(UNIXCREDS(skb), &siocb->scm->creds, sizeof(struct ucred));
if (siocb->scm->fp)
unix_attach_fds(siocb->scm, skb);
if (siocb->scm->fp) {
err = unix_attach_fds(siocb->scm, skb);
if (err)
goto out_free;
}
unix_get_secdata(siocb->scm, skb);
skb_reset_transport_header(skb);
@ -1538,8 +1550,13 @@ static int unix_stream_sendmsg(struct kiocb *kiocb, struct socket *sock,
size = min_t(int, size, skb_tailroom(skb));
memcpy(UNIXCREDS(skb), &siocb->scm->creds, sizeof(struct ucred));
if (siocb->scm->fp)
unix_attach_fds(siocb->scm, skb);
if (siocb->scm->fp) {
err = unix_attach_fds(siocb->scm, skb);
if (err) {
kfree_skb(skb);
goto out_err;
}
}
if ((err = memcpy_fromiovec(skb_put(skb,size), msg->msg_iov, size)) != 0) {
kfree_skb(skb);