From: Willem de Bruijn <willemb@xxxxxxxxxx> commit c27927e372f0785f3303e8fad94b85945e2c97b7 upstream. Updates to tp_reserve can race with reads of the field in packet_set_ring. Avoid this by holding the socket lock during updates in setsockopt PACKET_RESERVE. This bug was discovered by syzkaller. Fixes: 8913336a7e8d ("packet: add PACKET_RESERVE sockopt") Reported-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Willy Tarreau <w@xxxxxx> --- net/packet/af_packet.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index b915d01..2f22b07 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -3183,14 +3183,19 @@ packet_setsockopt(struct socket *sock, int level, int optname, char __user *optv if (optlen != sizeof(val)) return -EINVAL; - if (po->rx_ring.pg_vec || po->tx_ring.pg_vec) - return -EBUSY; if (copy_from_user(&val, optval, sizeof(val))) return -EFAULT; if (val > INT_MAX) return -EINVAL; - po->tp_reserve = val; - return 0; + lock_sock(sk); + if (po->rx_ring.pg_vec || po->tx_ring.pg_vec) { + ret = -EBUSY; + } else { + po->tp_reserve = val; + ret = 0; + } + release_sock(sk); + return ret; } case PACKET_LOSS: { -- 2.8.0.rc2.1.gbe9624a