4.4-stable review patch. If anyone has any objections, please let me know.
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From: Mike Maloney maloney@google.com
syzkaller found a race condition fanout_demux_rollover() while removing a packet socket from a fanout group.
po->rollover is read and operated on during packet_rcv_fanout(), via fanout_demux_rollover(), but the pointer is currently cleared before the synchronization in packet_release(). It is safer to delay the cleanup until after synchronize_net() has been called, ensuring all calls to packet_rcv_fanout() for this socket have finished.
To further simplify synchronization around the rollover structure, set po->rollover in fanout_add() only if there are no errors. This removes the need for rcu in the struct and in the call to packet_getsockopt(..., PACKET_ROLLOVER_STATS, ...).
Crashing stack trace: fanout_demux_rollover+0xb6/0x4d0 net/packet/af_packet.c:1392 packet_rcv_fanout+0x649/0x7c8 net/packet/af_packet.c:1487 dev_queue_xmit_nit+0x835/0xc10 net/core/dev.c:1953 xmit_one net/core/dev.c:2975 [inline] dev_hard_start_xmit+0x16b/0xac0 net/core/dev.c:2995 __dev_queue_xmit+0x17a4/0x2050 net/core/dev.c:3476 dev_queue_xmit+0x17/0x20 net/core/dev.c:3509 neigh_connected_output+0x489/0x720 net/core/neighbour.c:1379 neigh_output include/net/neighbour.h:482 [inline] ip6_finish_output2+0xad1/0x22a0 net/ipv6/ip6_output.c:120 ip6_finish_output+0x2f9/0x920 net/ipv6/ip6_output.c:146 NF_HOOK_COND include/linux/netfilter.h:239 [inline] ip6_output+0x1f4/0x850 net/ipv6/ip6_output.c:163 dst_output include/net/dst.h:459 [inline] NF_HOOK.constprop.35+0xff/0x630 include/linux/netfilter.h:250 mld_sendpack+0x6a8/0xcc0 net/ipv6/mcast.c:1660 mld_send_initial_cr.part.24+0x103/0x150 net/ipv6/mcast.c:2072 mld_send_initial_cr net/ipv6/mcast.c:2056 [inline] ipv6_mc_dad_complete+0x99/0x130 net/ipv6/mcast.c:2079 addrconf_dad_completed+0x595/0x970 net/ipv6/addrconf.c:4039 addrconf_dad_work+0xac9/0x1160 net/ipv6/addrconf.c:3971 process_one_work+0xbf0/0x1bc0 kernel/workqueue.c:2113 worker_thread+0x223/0x1990 kernel/workqueue.c:2247 kthread+0x35e/0x430 kernel/kthread.c:231 ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:432
Fixes: 0648ab70afe6 ("packet: rollover prepare: per-socket state") Fixes: 509c7a1ecc860 ("packet: avoid panic in packet_getsockopt()") Reported-by: syzbot syzkaller@googlegroups.com Signed-off-by: Mike Maloney maloney@google.com Reviewed-by: Eric Dumazet edumazet@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/packet/af_packet.c | 32 ++++++++++---------------------- net/packet/internal.h | 1 - 2 files changed, 10 insertions(+), 23 deletions(-)
--- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1665,7 +1665,6 @@ static int fanout_add(struct sock *sk, u atomic_long_set(&rollover->num, 0); atomic_long_set(&rollover->num_huge, 0); atomic_long_set(&rollover->num_failed, 0); - po->rollover = rollover; }
match = NULL; @@ -1710,6 +1709,8 @@ static int fanout_add(struct sock *sk, u if (atomic_read(&match->sk_ref) < PACKET_FANOUT_MAX) { __dev_remove_pack(&po->prot_hook); po->fanout = match; + po->rollover = rollover; + rollover = NULL; atomic_inc(&match->sk_ref); __fanout_link(sk, po); err = 0; @@ -1723,10 +1724,7 @@ static int fanout_add(struct sock *sk, u }
out: - if (err && rollover) { - kfree_rcu(rollover, rcu); - po->rollover = NULL; - } + kfree(rollover); mutex_unlock(&fanout_mutex); return err; } @@ -1750,11 +1748,6 @@ static struct packet_fanout *fanout_rele list_del(&f->list); else f = NULL; - - if (po->rollover) { - kfree_rcu(po->rollover, rcu); - po->rollover = NULL; - } } mutex_unlock(&fanout_mutex);
@@ -2914,6 +2907,7 @@ static int packet_release(struct socket synchronize_net();
if (f) { + kfree(po->rollover); fanout_release_data(f); kfree(f); } @@ -3771,7 +3765,6 @@ static int packet_getsockopt(struct sock void *data = &val; union tpacket_stats_u st; struct tpacket_rollover_stats rstats; - struct packet_rollover *rollover;
if (level != SOL_PACKET) return -ENOPROTOOPT; @@ -3850,18 +3843,13 @@ static int packet_getsockopt(struct sock 0); break; case PACKET_ROLLOVER_STATS: - 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) + 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); + data = &rstats; + lv = sizeof(rstats); break; case PACKET_TX_HAS_OFF: val = po->tp_tx_has_off; --- a/net/packet/internal.h +++ b/net/packet/internal.h @@ -92,7 +92,6 @@ struct packet_fanout {
struct packet_rollover { int sock; - struct rcu_head rcu; atomic_long_t num; atomic_long_t num_huge; atomic_long_t num_failed;