From f98f4514d07871da7a113dd9e3e330743fd70ae4 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 16 Jun 2015 07:59:11 -0700 Subject: packet: read num_members once in packet_rcv_fanout() We need to tell compiler it must not read f->num_members multiple times. Otherwise testing if num is not zero is flaky, and we could attempt an invalid divide by 0 in fanout_demux_cpu() Note bug was present in packet_rcv_fanout_hash() and packet_rcv_fanout_lb() but final 3.1 had a simple location after commit 95ec3eb417115fb ("packet: Add 'cpu' fanout policy.") Fixes: dc99f600698dc ("packet: Add fanout support.") Signed-off-by: Eric Dumazet Cc: Willem de Bruijn Signed-off-by: David S. Miller --- net/packet/af_packet.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'net/packet') diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index b5989c6ee551..131545a06f05 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1353,7 +1353,7 @@ static int packet_rcv_fanout(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt, struct net_device *orig_dev) { struct packet_fanout *f = pt->af_packet_priv; - unsigned int num = f->num_members; + unsigned int num = READ_ONCE(f->num_members); struct packet_sock *po; unsigned int idx; -- cgit v1.2.3-59-g8ed1b From 468479e6043c84f5a65299cc07cb08a22a28c2b1 Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Wed, 17 Jun 2015 15:59:34 -0400 Subject: 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(-) (limited to 'net/packet') diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 131545a06f05..fe1610ddeacf 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, -- cgit v1.2.3-59-g8ed1b