net: unix: fix inflight counting bug in garbage collector
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>
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 4d3c607..eb90f77 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1302,14 +1302,23 @@
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 @@
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 @@
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);
