[PATCH 4.4 09/18] netlink: annotate data races around nlk->bound

Greg Kroah-Hartman
2021-10-14T14:55:44Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 7707a4d01a648e4c655101a469c956cb11273655 ]

While existing code is correct, KCSAN is reporting
a data-race in netlink_insert / netlink_sendmsg [1]

It is correct to read nlk->bound without a lock, as netlink_autobind()
will acquire all needed locks.

[1]
BUG: KCSAN: data-race in netlink_insert / netlink_sendmsg

write to 0xffff8881031c8b30 of 1 bytes by task 18752 on cpu 0:
netlink_insert+0x5cc/0x7f0 net/netlink/af_netlink.c:597
netlink_autobind+0xa9/0x150 net/netlink/af_netlink.c:842
netlink_sendmsg+0x479/0x7c0 net/netlink/af_netlink.c:1892
sock_sendmsg_nosec net/socket.c:703 [inline]
sock_sendmsg net/socket.c:723 [inline]
____sys_sendmsg+0x360/0x4d0 net/socket.c:2392
___sys_sendmsg net/socket.c:2446 [inline]
__sys_sendmsg+0x1ed/0x270 net/socket.c:2475
__do_sys_sendmsg net/socket.c:2484 [inline]
__se_sys_sendmsg net/socket.c:2482 [inline]
__x64_sys_sendmsg+0x42/0x50 net/socket.c:2482
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881031c8b30 of 1 bytes by task 18751 on cpu 1:
netlink_sendmsg+0x270/0x7c0 net/netlink/af_netlink.c:1891
sock_sendmsg_nosec net/socket.c:703 [inline]
sock_sendmsg net/socket.c:723 [inline]
__sys_sendto+0x2a8/0x370 net/socket.c:2019
__do_sys_sendto net/socket.c:2031 [inline]
__se_sys_sendto net/socket.c:2027 [inline]
__x64_sys_sendto+0x74/0x90 net/socket.c:2027
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 18751 Comm: syz-executor.0 Not tainted 5.14.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Fixes: da314c9923fe ("netlink: Replace rhash_portid with bound")
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/netlink/af_netlink.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 260cba93a2cf..65cf129eaad3 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -574,7 +574,10 @@ static int netlink_insert(struct sock *sk, u32 portid)

/* We need to ensure that the socket is hashed and visible. */
smp_wmb();
- nlk_sk(sk)->bound = portid;
+ /* Paired with lockless reads from netlink_bind(),
+ * netlink_connect() and netlink_sendmsg().
+ */
+ WRITE_ONCE(nlk_sk(sk)->bound, portid);

err:
release_sock(sk);
@@ -993,7 +996,8 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
else if (nlk->ngroups < 8*sizeof(groups))
groups &= (1UL << nlk->ngroups) - 1;

- bound = nlk->bound;
+ /* Paired with WRITE_ONCE() in netlink_insert() */
+ bound = READ_ONCE(nlk->bound);
if (bound) {
/* Ensure nlk->portid is up-to-date. */
smp_rmb();
@@ -1073,8 +1077,9 @@ static int netlink_connect(struct socket *sock, struct sockaddr *addr,

/* No need for barriers here as we return to user-space without
* using any of the bound attributes.
+ * Paired with WRITE_ONCE() in netlink_insert().
*/
- if (!nlk->bound)
+ if (!READ_ONCE(nlk->bound))
err = netlink_autobind(sock);

if (err == 0) {
@@ -1821,7 +1826,8 @@ static int netlink_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
dst_group = nlk->dst_group;
}

- if (!nlk->bound) {
+ /* Paired with WRITE_ONCE() in netlink_insert() */
+ if (!READ_ONCE(nlk->bound)) {
err = netlink_autobind(sock);
if (err)
goto out;
--
2.33.0