4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Mike Maloney <maloney@xxxxxxxxxx>
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@xxxxxxxxxxxxxxxx>
Signed-off-by: Mike Maloney <maloney@xxxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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
@@ -1661,7 +1661,6 @@ 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;
@@ -1706,6 +1705,8 @@ 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;
@@ -1719,10 +1720,7 @@ 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;
}
@@ -1746,11 +1744,6 @@ 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);
@@ -3039,6 +3032,7 @@ static int packet_release(struct socket
synchronize_net();
if (f) {
+ kfree(po->rollover);
fanout_release_data(f);
kfree(f);
}
@@ -3853,7 +3847,6 @@ 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;
@@ -3932,18 +3925,13 @@ 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;