| From | Ben Hutchings <> | Date | Sun, 02 Aug 2015 01:02:38 +0100 | Subject | [PATCH 3.2 138/164] packet: avoid out of bounds read in round robin fanout |
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3.2.70-rc1 review patch. If anyone has any objections, please let me know.
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From: Willem de Bruijn <willemb@google.com>
[ 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.
Fixes: dc99f600698d ("packet: Add fanout support.") Suggested-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Willem de Bruijn <willemb@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> [bwh: Backported to 3.2: - Adjust context - Demux functions return a sock pointer, not an index] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- net/packet/af_packet.c | 18 ++---------------- 1 file changed, 2 insertions(+), 16 deletions(-)
--- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1170,16 +1170,6 @@ 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 struct sock *fanout_demux_hash(struct packet_fanout *f, struct sk_buff *skb, unsigned int num) { u32 idx, hash = skb->rxhash; @@ -1191,13 +1181,9 @@ static struct sock *fanout_demux_hash(st static struct sock *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 f->arr[cur]; + return f->arr[val % num]; } static struct sock *fanout_demux_cpu(struct packet_fanout *f, struct sk_buff *skb, unsigned int num)
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