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packet: avoid out of bounds read in round robin fanout

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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>
This commit is contained in:
Willem de Bruijn 2015-06-17 15:59:34 -04:00 committed by David S. Miller
parent 51f458d961
commit 468479e604
1 changed files with 2 additions and 16 deletions
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18
net/packet/af_packet.c
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@ -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,