From 509c7a1ecc8601f94ffba8a00889fefb239c00c6 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 18 Oct 2017 16:14:52 -0700 Subject: [PATCH] packet: avoid panic in packet_getsockopt() 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: a9b6391814d5 ("packet: rollover statistics") Signed-off-by: Eric Dumazet Cc: Willem de Bruijn Cc: John Sperbeck Signed-off-by: David S. Miller --- net/packet/af_packet.c | 24 ++++++++++++++++-------- 1 file changed, 16 insertions(+), 8 deletions(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index bec01a3daf5b..2986941164b1 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1769,7 +1769,7 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags) out: if (err && rollover) { - kfree(rollover); + kfree_rcu(rollover, rcu); po->rollover = NULL; } mutex_unlock(&fanout_mutex); @@ -1796,8 +1796,10 @@ static struct packet_fanout *fanout_release(struct sock *sk) else f = NULL; - if (po->rollover) + if (po->rollover) { kfree_rcu(po->rollover, rcu); + po->rollover = NULL; + } } mutex_unlock(&fanout_mutex); @@ -3851,6 +3853,7 @@ static int packet_getsockopt(struct socket *sock, int level, int optname, void *data = &val; union tpacket_stats_u st; struct tpacket_rollover_stats rstats; + struct packet_rollover *rollover; if (level != SOL_PACKET) return -ENOPROTOOPT; @@ -3929,13 +3932,18 @@ static int packet_getsockopt(struct socket *sock, int level, int optname, 0); break; case PACKET_ROLLOVER_STATS: - if (!po->rollover) + rcu_read_lock(); + rollover = rcu_dereference(po->rollover); + if (rollover) { + rstats.tp_all = atomic_long_read(&rollover->num); + rstats.tp_huge = atomic_long_read(&rollover->num_huge); + rstats.tp_failed = atomic_long_read(&rollover->num_failed); + data = &rstats; + lv = sizeof(rstats); + } + rcu_read_unlock(); + if (!rollover) return -EINVAL; - rstats.tp_all = atomic_long_read(&po->rollover->num); - rstats.tp_huge = atomic_long_read(&po->rollover->num_huge); - rstats.tp_failed = atomic_long_read(&po->rollover->num_failed); - data = &rstats; - lv = sizeof(rstats); break; case PACKET_TX_HAS_OFF: val = po->tp_tx_has_off; -- 2.20.1