Commit 154dcd0b authored Jun 17, 2015 by Willem de Bruijn Committed by Sasha Levin Jul 05, 2015

packet: avoid out of bounds read in round robin fanout



[ 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: dc99f600 ("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>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

parent 5c0e1a6b

net/packet/af_packet.c

+2 −16

Original line number	Diff line number	Diff line
		@@ -1255,16 +1255,6 @@ 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)
		@@ -1276,13 +1266,9 @@ 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,