[PATCH AUTOSEL 4.19 08/16] net/packet: annotate accesses to po->bind

Sasha Levin
2021-06-21T18:04:02Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit c7d2ef5dd4b03ed0ee1d13bc0c55f9cf62d49bd6 ]

tpacket_snd(), packet_snd(), packet_getname() and packet_seq_show()
can read po->num without holding a lock. This means other threads
can change po->num at the same time.

KCSAN complained about this known fact [1]
Add READ_ONCE()/WRITE_ONCE() to address the issue.

[1] BUG: KCSAN: data-race in packet_do_bind / packet_sendmsg

write to 0xffff888131a0dcc0 of 2 bytes by task 24714 on cpu 0:
packet_do_bind+0x3ab/0x7e0 net/packet/af_packet.c:3181
packet_bind+0xc3/0xd0 net/packet/af_packet.c:3255
__sys_bind+0x200/0x290 net/socket.c:1637
__do_sys_bind net/socket.c:1648 [inline]
__se_sys_bind net/socket.c:1646 [inline]
__x64_sys_bind+0x3d/0x50 net/socket.c:1646
do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888131a0dcc0 of 2 bytes by task 24719 on cpu 1:
packet_snd net/packet/af_packet.c:2899 [inline]
packet_sendmsg+0x317/0x3570 net/packet/af_packet.c:3040
sock_sendmsg_nosec net/socket.c:654 [inline]
sock_sendmsg net/socket.c:674 [inline]
____sys_sendmsg+0x360/0x4d0 net/socket.c:2350
___sys_sendmsg net/socket.c:2404 [inline]
__sys_sendmsg+0x1ed/0x270 net/socket.c:2433
__do_sys_sendmsg net/socket.c:2442 [inline]
__se_sys_sendmsg net/socket.c:2440 [inline]
__x64_sys_sendmsg+0x42/0x50 net/socket.c:2440
do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000 -> 0x1200

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 24719 Comm: syz-executor.5 Not tainted 5.13.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/packet/af_packet.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 16b745d254fe..42299fa02038 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2656,7 +2656,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
}
if (likely(saddr == NULL)) {
dev = packet_cached_dev_get(po);
- proto = po->num;
+ proto = READ_ONCE(po->num);
} else {
err = -EINVAL;
if (msg->msg_namelen < sizeof(struct sockaddr_ll))
@@ -2869,7 +2869,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)

if (likely(saddr == NULL)) {
dev = packet_cached_dev_get(po);
- proto = po->num;
+ proto = READ_ONCE(po->num);
} else {
err = -EINVAL;
if (msg->msg_namelen < sizeof(struct sockaddr_ll))
@@ -3141,7 +3141,7 @@ static int packet_do_bind(struct sock *sk, const char *name, int ifindex,
/* prevents packet_notifier() from calling
* register_prot_hook()
*/
- po->num = 0;
+ WRITE_ONCE(po->num, 0);
__unregister_prot_hook(sk, true);
rcu_read_lock();
dev_curr = po->prot_hook.dev;
@@ -3151,7 +3151,7 @@ static int packet_do_bind(struct sock *sk, const char *name, int ifindex,
}

BUG_ON(po->running);
- po->num = proto;
+ WRITE_ONCE(po->num, proto);
po->prot_hook.type = proto;

if (unlikely(unlisted)) {
@@ -3497,7 +3497,7 @@ static int packet_getname(struct socket *sock, struct sockaddr *uaddr,

sll->sll_family = AF_PACKET;
sll->sll_ifindex = po->ifindex;
- sll->sll_protocol = po->num;
+ sll->sll_protocol = READ_ONCE(po->num);
sll->sll_pkttype = 0;
rcu_read_lock();
dev = dev_get_by_index_rcu(sock_net(sk), po->ifindex);
@@ -4391,7 +4391,7 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
was_running = po->running;
num = po->num;
if (was_running) {
- po->num = 0;
+ WRITE_ONCE(po->num, 0);
__unregister_prot_hook(sk, false);
}
spin_unlock(&po->bind_lock);
@@ -4426,7 +4426,7 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,

spin_lock(&po->bind_lock);
if (was_running) {
- po->num = num;
+ WRITE_ONCE(po->num, num);
register_prot_hook(sk);
}
spin_unlock(&po->bind_lock);
@@ -4597,7 +4597,7 @@ static int packet_seq_show(struct seq_file *seq, void *v)
s,
refcount_read(&s->sk_refcnt),
s->sk_type,
- ntohs(po->num),
+ ntohs(READ_ONCE(po->num)),
po->ifindex,
po->running,
atomic_read(&s->sk_rmem_alloc),
--
2.30.2