From 468479e6043c84f5a65299cc07cb08a22a28c2b1 Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Wed, 17 Jun 2015 15:59:34 -0400 Subject: [PATCH] packet: avoid out of bounds read in round robin fanout 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. Fixes: dc99f600698d ("packet: Add fanout support.") Suggested-by: Eric Dumazet Signed-off-by: Willem de Bruijn Acked-by: Eric Dumazet Signed-off-by: David S. Miller --- net/packet/af_packet.c | 18 ++---------------- 1 file changed, 2 insertions(+), 16 deletions(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 131545a..fe1610d 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1272,16 +1272,6 @@ static void packet_sock_destruct(struct sock *sk) 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(struct packet_fanout *f, 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, -- 2.7.4