Commit 509c7a1e authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

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: a9b63918 ("packet: rollover statistics")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: John Sperbeck <jsperbeck@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c92e8c02

net/packet/af_packet.c

+16 −8
Original line number Diff line number Diff line
@@ -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)

			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);

		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;

		break;

	case PACKET_TX_HAS_OFF:

		val = po->tp_tx_has_off;

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