packet: avoid out of bounds read in round robin fanout (468479e6) · Commits · 戴 / test

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: ("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>

net/packet/af_packet.c

+2 −16

Original line number	Diff line number	Diff line
		@@ -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,

Admin message