Commit c5e79731 authored by Willem de Bruijn's avatar Willem de Bruijn Committed by Luis Henriques

packet: avoid out of bounds read in round robin fanout

commit 468479e6 upstream.

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: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarWillem de Bruijn <willemb@google.com>
Acked-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent 95e32b4e
...@@ -1265,16 +1265,6 @@ static void packet_sock_destruct(struct sock *sk) ...@@ -1265,16 +1265,6 @@ static void packet_sock_destruct(struct sock *sk)
sk_refcnt_debug_dec(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, static unsigned int fanout_demux_hash(struct packet_fanout *f,
struct sk_buff *skb, struct sk_buff *skb,
unsigned int num) unsigned int num)
...@@ -1286,13 +1276,9 @@ static unsigned int fanout_demux_lb(struct packet_fanout *f, ...@@ -1286,13 +1276,9 @@ static unsigned int fanout_demux_lb(struct packet_fanout *f,
struct sk_buff *skb, struct sk_buff *skb,
unsigned int num) unsigned int num)
{ {
int cur, old; unsigned int val = atomic_inc_return(&f->rr_cur);
cur = atomic_read(&f->rr_cur); return val % num;
while ((old = atomic_cmpxchg(&f->rr_cur, cur,
fanout_rr_next(f, num))) != cur)
cur = old;
return cur;
} }
static unsigned int fanout_demux_cpu(struct packet_fanout *f, static unsigned int fanout_demux_cpu(struct packet_fanout *f,
......
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