Patch "packet: avoid out of bounds read in round robin fanout" has been added to the 4.1-stable tree

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

packet: avoid out of bounds read in round robin fanout

to the 4.1-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-avoid-out-of-bounds-read-in-round-robin-fanout.patch
and it can be found in the queue-4.1 subdirectory.

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

From: Willem de Bruijn <[email protected]>
Date: Wed, 17 Jun 2015 15:59:34 -0400
Subject: packet: avoid out of bounds read in round robin fanout

From: Willem de Bruijn <[email protected]>

[ Upstream commit 468479e6043c84f5a65299cc07cb08a22a28c2b1 ]

PACKET_FANOUT_LB computes f->rr_cur such that it is modulo f->num_members. It returns the old value unconditionally, but f->num_members may have changed since the last store. Ensure that the return value is always < num.

When modifying the logic, simplify it further by replacing the loop with an unconditional atomic increment.

---
 net/packet/af_packet.c |   18 ++----------------
 1 file changed, 2 insertions(+), 16 deletions(-)

@@ -1272,16 +1272,6 @@ static void packet_sock_destruct(struct
 	sk_refcnt_debug_dec(sk);
 }
 
-static int fanout_rr_next(struct packet_fanout *f, unsigned int num)
-{
-	int x = atomic_read(&f->rr_cur) + 1;
-
-	if (x >= num)
-		x = 0;
-
-	return x;
-}
-
 static unsigned int fanout_demux_hash(struct packet_fanout *f,
 				      struct sk_buff *skb,
 				      unsigned int num)

@@ -1293,13 +1283,9 @@ static unsigned int fanout_demux_lb(stru
 				    struct sk_buff *skb,
 				    unsigned int num)
 {
-	int cur, old;
+	unsigned int val = atomic_inc_return(&f->rr_cur);
 
-	cur = atomic_read(&f->rr_cur);
-	while ((old = atomic_cmpxchg(&f->rr_cur, cur,
-				     fanout_rr_next(f, num))) != cur)
-		cur = old;
-	return cur;
+	return val % num;
 }
 
 static unsigned int fanout_demux_cpu(struct packet_fanout *f,

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

queue-4.1/packet-avoid-out-of-bounds-read-in-round-robin-fanout.patch queue-4.1/packet-read-num_members-once-in-packet_rcv_fanout.patch queue-4.1/ip-report-the-original-address-of-icmp-messages.patch