CVE-2022-49979

In the Linux kernel, the following vulnerability has been resolved:

net: fix refcount bug in sk_psock_get (2)

Syzkaller reports 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

<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>

During SMC fallback process in connect syscall, kernel will

replaces TCP with SMC. In order to forward wakeup

smc socket waitqueue after fallback, kernel will sets

clcsk->sk_user_data to origin smc socket in

smc_fback_replace_callbacks().

Later, in shutdown syscall, kernel will calls

sk_psock_get(), which treats the clcsk->sk_user_data

as psock type, triggering the refcnt warning.

So, the root cause is that smc and psock, both will use

sk_user_data field. So they will mismatch this field

easily.

This patch solves it by using another bit(defined as

SK_USER_DATA_PSOCK) in PTRMASK, to mark whether

sk_user_data points to a psock object or not.

This patch depends on a PTRMASK introduced in commit f1ff5ce2cd5e

("net, sk_msg: Clear sk_user_data pointer on clone if tagged").

For there will possibly be more flags in the sk_user_data field,

this patch also refactor sk_user_data flags code to be more generic

to improve its maintainability.