From: hawk <18801353760@xxxxxxx>
Syzkaller reportes refcount bug as follows:
------------[ cut here ]------------
refcount_t: saturated; leaking memory.
WARNING: CPU: 1 PID: 3605 at lib/refcount.c:19 refcount_warn_saturate+0xf4/0x1e0 lib/refcount.c:19
Modules linked in:
CPU: 1 PID: 3605 Comm: syz-executor208 Not tainted 5.18.0-syzkaller-03023-g7e062cda7d90 #0
...
Call Trace:
<TASK>
__refcount_add_not_zero include/linux/refcount.h:163 [inline]
__refcount_inc_not_zero include/linux/refcount.h:227 [inline]
refcount_inc_not_zero include/linux/refcount.h:245 [inline]
sk_psock_get+0x3bc/0x410 include/linux/skmsg.h:439
tls_data_ready+0x6d/0x1b0 net/tls/tls_sw.c:2091
tcp_data_ready+0x106/0x520 net/ipv4/tcp_input.c:4983
tcp_data_queue+0x25f2/0x4c90 net/ipv4/tcp_input.c:5057
tcp_rcv_state_process+0x1774/0x4e80 net/ipv4/tcp_input.c:6659
tcp_v4_do_rcv+0x339/0x980 net/ipv4/tcp_ipv4.c:1682
sk_backlog_rcv include/net/sock.h:1061 [inline]
__release_sock+0x134/0x3b0 net/core/sock.c:2849
release_sock+0x54/0x1b0 net/core/sock.c:3404
inet_shutdown+0x1e0/0x430 net/ipv4/af_inet.c:909
__sys_shutdown_sock net/socket.c:2331 [inline]
__sys_shutdown_sock net/socket.c:2325 [inline]
__sys_shutdown+0xf1/0x1b0 net/socket.c:2343
__do_sys_shutdown net/socket.c:2351 [inline]
__se_sys_shutdown net/socket.c:2349 [inline]
__x64_sys_shutdown+0x50/0x70 net/socket.c:2349
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x46/0xb0
</TASK>
syzbot is try to setup TLS on a SMC socket.
During SMC fallback process in connect syscall, kernel will sets the
smc->sk.sk_socket->file->private_data to smc->clcsock
in smc_switch_to_fallback(), and set smc->clcsock->sk_user_data
to origin smc in smc_fback_replace_callbacks().
When syzbot makes a setsockopt syscall, its argument sockfd
actually points to smc->clcsock, which is not a smc_sock type,
So it won't call smc_setsockopt() in setsockopt syscall,
instead it will call do_tcp_setsockopt() to setup TLS, which
bypasses the fixes 734942cc4ea6, its content is shown as below
> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
> index be3e80b3e27f1..5eff7cccceffc 100644
> --- a/net/smc/af_smc.c
> +++ b/net/smc/af_smc.c
> @@ -2161,6 +2161,9 @@ static int smc_setsockopt(struct socket *sock,
> int level, int optname,
> struct smc_sock *smc;
> int val, rc;
>
> + if (level == SOL_TCP && optname == TCP_ULP)
> + return -EOPNOTSUPP;
> +
> smc = smc_sk(sk);
>
> /* generic setsockopts reaching us here always apply to the
> @@ -2185,7 +2188,6 @@ static int smc_setsockopt(struct socket *sock,
> int level, int optname,
> if (rc || smc->use_fallback)
> goto out;
> switch (optname) {
> - case TCP_ULP:
> case TCP_FASTOPEN:
> case TCP_FASTOPEN_CONNECT:
> case TCP_FASTOPEN_KEY:
> --
Later, sk_psock_get() will treat the smc->clcsock->sk_user_data
as sk_psock type, which triggers the refcnt warning.
So Just disallow this setup in do_tcp_setsockopt() is OK,
by checking whether sk_user_data points to a SMC socket.
Reported-and-tested-by: syzbot+5f26f85569bd179c18ce@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: hawk <18801353760@xxxxxxx>
---
net/ipv4/tcp.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 9984d23a7f3e..a1e6cab2c748 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3395,10 +3395,23 @@ static int do_tcp_setsockopt(struct sock *sk, int level, int optname,
}
case TCP_ULP: {
char name[TCP_ULP_NAME_MAX];
+ struct sock *smc_sock;
if (optlen < 1)
return -EINVAL;
+ /* SMC sk_user_data may be treated as psock,
+ * which triggers a refcnt warning.
+ */
+ rcu_read_lock();
+ smc_sock = rcu_dereference_sk_user_data(sk);
+ if (level == SOL_TCP && smc_sock &&
+ smc_sock->__sk_common.skc_family == AF_SMC) {
+ rcu_read_unlock();
+ return -EOPNOTSUPP;
+ }
+ rcu_read_unlock();
+
val = strncpy_from_sockptr(name, optval,
min_t(long, TCP_ULP_NAME_MAX - 1,
optlen));
--
2.25.1
