Patch "packet: fix use-after-free in prb_retire_rx_blk_timer_expired()" has been added to the 4.12-stable tree

This is a note to let you know that I've just added the patch titled

packet: fix use-after-free in prb_retire_rx_blk_timer_expired()

to the 4.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
packet-fix-use-after-free-in-prb_retire_rx_blk_timer_expired.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: WANG Cong <[email protected]>
Date: Mon, 24 Jul 2017 10:07:32 -0700
Subject: packet: fix use-after-free in prb_retire_rx_blk_timer_expired()

From: WANG Cong <[email protected]>

[ Upstream commit c800aaf8d869f2b9b47b10c5c312fe19f0a94042 ]

There are multiple reports showing we have a use-after-free in the timer prb_retire_rx_blk_timer_expired(), where we use struct tpacket_kbdq_core::pkbdq, a pg_vec, after it gets freed by free_pg_vec().

The interesting part is it is not freed via packet_release() but via packet_setsockopt(), which means we are not closing the socket. Looking into the big and fat function packet_set_ring(), this could happen if we satisfy the following conditions:

1. closing == 0, not on packet_release() path
2. req->tp_block_nr == 0, we don't allocate a new pg_vec
3. rx_ring->pg_vec is already set as V3, which means we already called packet_set_ring() wtih req->tp_block_nr > 0 previously
4. req->tp_frame_nr == 0, pass sanity check
5. po->mapped == 0, never called mmap()

In this scenario we are clearing the old rx_ring->pg_vec, so we need to free this pg_vec, but we don't stop the timer on this path because of closing==0.

The timer has to be stopped as long as we need to free pg_vec, therefore the check on closing!=0 is wrong, we should check pg_vec!=NULL instead.

Thanks to liujian for testing different fixes.

---
 net/packet/af_packet.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -4334,7 +4334,7 @@ static int packet_set_ring(struct sock *
 		register_prot_hook(sk);
 	}
 	spin_unlock(&po->bind_lock);
-	if (closing && (po->tp_version > TPACKET_V2)) {
+	if (pg_vec && (po->tp_version > TPACKET_V2)) {
 		/* Because we don't support block-based V3 on tx-ring */
 		if (!tx_ring)
 			prb_shutdown_retire_blk_timer(po, rb_queue);

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/packet-fix-use-after-free-in-prb_retire_rx_blk_timer_expired.patch queue-4.12/rtnetlink-allocate-more-memory-for-dev_set_mac_address.patch queue-4.12/bonding-commit-link-status-change-after-propose.patch