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packet: avoid panic in packet_getsockopt()

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syzkaller got crashes in packet_getsockopt() processing
PACKET_ROLLOVER_STATS command while another thread was managing
to change po->rollover

Using RCU will fix this bug. We might later add proper RCU annotations
for sparse sake.

In v2: I replaced kfree(rollover) in fanout_add() to kfree_rcu()
variant, as spotted by John.

Fixes: a9b6391814 ("packet: rollover statistics")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: John Sperbeck <jsperbeck@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2017-10-18 16:14:52 -07:00 committed by David S. Miller
parent c92e8c02fe
commit 509c7a1ecc
1 changed files with 16 additions and 8 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

22
net/packet/af_packet.c
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@ -1769,7 +1769,7 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
out: out:
if (err && rollover) { if (err && rollover) {
kfree(rollover); kfree_rcu(rollover, rcu);
po->rollover = NULL; po->rollover = NULL;
} }
mutex_unlock(&fanout_mutex); mutex_unlock(&fanout_mutex);
@ -1796,8 +1796,10 @@ static struct packet_fanout *fanout_release(struct sock *sk)
else else
f = NULL; f = NULL;
if (po->rollover) if (po->rollover) {
kfree_rcu(po->rollover, rcu); kfree_rcu(po->rollover, rcu);
po->rollover = NULL;
}
} }
mutex_unlock(&fanout_mutex); mutex_unlock(&fanout_mutex);
@ -3851,6 +3853,7 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
void *data = &val; void *data = &val;
union tpacket_stats_u st; union tpacket_stats_u st;
struct tpacket_rollover_stats rstats; struct tpacket_rollover_stats rstats;
struct packet_rollover *rollover;
if (level != SOL_PACKET) if (level != SOL_PACKET)
return -ENOPROTOOPT; return -ENOPROTOOPT;
@ -3929,13 +3932,18 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
0); 0);
break; break;
case PACKET_ROLLOVER_STATS: case PACKET_ROLLOVER_STATS:
if (!po->rollover) rcu_read_lock();
return -EINVAL; rollover = rcu_dereference(po->rollover);
rstats.tp_all = atomic_long_read(&po->rollover->num); if (rollover) {
rstats.tp_huge = atomic_long_read(&po->rollover->num_huge); rstats.tp_all = atomic_long_read(&rollover->num);
rstats.tp_failed = atomic_long_read(&po->rollover->num_failed); rstats.tp_huge = atomic_long_read(&rollover->num_huge);
rstats.tp_failed = atomic_long_read(&rollover->num_failed);
data = &rstats; data = &rstats;
lv = sizeof(rstats); lv = sizeof(rstats);
}
rcu_read_unlock();
if (!rollover)
return -EINVAL;
break; break;
case PACKET_TX_HAS_OFF: case PACKET_TX_HAS_OFF:
val = po->tp_tx_has_off; val = po->tp_tx_has_off;