[PATCH 4.9 63/71] net/packet: annotate accesses to po->ifindex

Sasha Levin
2021-06-28T15:22:23Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit e032f7c9c7cefffcfb79b9fc16c53011d2d9d11f ]

Like prior patch, we need to annotate lockless accesses to po->ifindex
For instance, packet_getname() is reading po->ifindex (twice) while
another thread is able to change po->ifindex.

KCSAN reported:

BUG: KCSAN: data-race in packet_do_bind / packet_getname

write to 0xffff888143ce3cbc of 4 bytes by task 25573 on cpu 1:
packet_do_bind+0x420/0x7e0 net/packet/af_packet.c:3191
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 0xffff888143ce3cbc of 4 bytes by task 25578 on cpu 0:
packet_getname+0x5b/0x1a0 net/packet/af_packet.c:3525
__sys_getsockname+0x10e/0x1a0 net/socket.c:1887
__do_sys_getsockname net/socket.c:1902 [inline]
__se_sys_getsockname net/socket.c:1899 [inline]
__x64_sys_getsockname+0x3e/0x50 net/socket.c:1899
do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000000 -> 0x00000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 25578 Comm: syz-executor.5 Not tainted 5.13.0-rc6-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, 9 insertions(+), 7 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 5f9007e7c28d..370d0a4af1f9 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3173,11 +3173,11 @@ static int packet_do_bind(struct sock *sk, const char *name, int ifindex,
if (unlikely(unlisted)) {
dev_put(dev);
po->prot_hook.dev = NULL;
- po->ifindex = -1;
+ WRITE_ONCE(po->ifindex, -1);
packet_cached_dev_reset(po);
} else {
po->prot_hook.dev = dev;
- po->ifindex = dev ? dev->ifindex : 0;
+ WRITE_ONCE(po->ifindex, dev ? dev->ifindex : 0);
packet_cached_dev_assign(po, dev);
}
}
@@ -3492,7 +3492,7 @@ static int packet_getname_spkt(struct socket *sock, struct sockaddr *uaddr,
uaddr->sa_family = AF_PACKET;
memset(uaddr->sa_data, 0, sizeof(uaddr->sa_data));
rcu_read_lock();
- dev = dev_get_by_index_rcu(sock_net(sk), pkt_sk(sk)->ifindex);
+ dev = dev_get_by_index_rcu(sock_net(sk), READ_ONCE(pkt_sk(sk)->ifindex));
if (dev)
strlcpy(uaddr->sa_data, dev->name, sizeof(uaddr->sa_data));
rcu_read_unlock();
@@ -3508,16 +3508,18 @@ static int packet_getname(struct socket *sock, struct sockaddr *uaddr,
struct sock *sk = sock->sk;
struct packet_sock *po = pkt_sk(sk);
DECLARE_SOCKADDR(struct sockaddr_ll *, sll, uaddr);
+ int ifindex;

if (peer)
return -EOPNOTSUPP;

+ ifindex = READ_ONCE(po->ifindex);
sll->sll_family = AF_PACKET;
- sll->sll_ifindex = po->ifindex;
+ sll->sll_ifindex = ifindex;
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);
+ dev = dev_get_by_index_rcu(sock_net(sk), ifindex);
if (dev) {
sll->sll_hatype = dev->type;
sll->sll_halen = dev->addr_len;
@@ -4097,7 +4099,7 @@ static int packet_notifier(struct notifier_block *this,
}
if (msg == NETDEV_UNREGISTER) {
packet_cached_dev_reset(po);
- po->ifindex = -1;
+ WRITE_ONCE(po->ifindex, -1);
if (po->prot_hook.dev)
dev_put(po->prot_hook.dev);
po->prot_hook.dev = NULL;
@@ -4603,7 +4605,7 @@ static int packet_seq_show(struct seq_file *seq, void *v)
atomic_read(&s->sk_refcnt),
s->sk_type,
ntohs(READ_ONCE(po->num)),
- po->ifindex,
+ READ_ONCE(po->ifindex),
po->running,
atomic_read(&s->sk_rmem_alloc),
from_kuid_munged(seq_user_ns(seq), sock_i_uid(s)),
--
2.30.2