[PATCH 5.15 269/570] net/smc: Fix slab-out-of-bounds issue in fallback

Greg Kroah-Hartman
2026-04-13T16:31:02Z

From: Wen Gu <guwen@linux.alibaba.com>

[ Upstream commit 0558226cebee256aa3f8ec0cc5a800a10bf120a6 ]

syzbot reported a slab-out-of-bounds/use-after-free issue,
which was caused by accessing an already freed smc sock in
fallback-specific callback functions of clcsock.

This patch fixes the issue by restoring fallback-specific
callback functions to original ones and resetting clcsock
sk_user_data to NULL before freeing smc sock.

Meanwhile, this patch introduces sk_callback_lock to make
the access and assignment to sk_user_data mutually exclusive.

Reported-by: syzbot+b425899ed22c6943e00b@syzkaller.appspotmail.com
Fixes: 341adeec9ada ("net/smc: Forward wakeup to smc socket waitqueue after fallback")
Link: https://lore.kernel.org/r/00000000000013ca8105d7ae3ada@google.com/
Signed-off-by: Wen Gu <guwen@linux.alibaba.com>
Acked-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 6d5e4538364b ("net/smc: fix NULL dereference and UAF in smc_tcp_syn_recv_sock()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/smc/af_smc.c | 80 ++++++++++++++++++++++++++++++++-------------
net/smc/smc_close.c | 2 ++
2 files changed, 59 insertions(+), 23 deletions(-)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 5c6759d2e271d..ea1a185327629 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -170,11 +170,27 @@ struct proto smc_proto6 = {
};
EXPORT_SYMBOL_GPL(smc_proto6);

+static void smc_fback_restore_callbacks(struct smc_sock *smc)
+{
+ struct sock *clcsk = smc->clcsock->sk;
+
+ write_lock_bh(&clcsk->sk_callback_lock);
+ clcsk->sk_user_data = NULL;
+
+ smc_clcsock_restore_cb(&clcsk->sk_state_change, &smc->clcsk_state_change);
+ smc_clcsock_restore_cb(&clcsk->sk_data_ready, &smc->clcsk_data_ready);
+ smc_clcsock_restore_cb(&clcsk->sk_write_space, &smc->clcsk_write_space);
+ smc_clcsock_restore_cb(&clcsk->sk_error_report, &smc->clcsk_error_report);
+
+ write_unlock_bh(&clcsk->sk_callback_lock);
+}
+
static void smc_restore_fallback_changes(struct smc_sock *smc)
{
if (smc->clcsock->file) { /* non-accepted sockets have no file yet */
smc->clcsock->file->private_data = smc->sk.sk_socket;
smc->clcsock->file = NULL;
+ smc_fback_restore_callbacks(smc);
}
}

@@ -659,48 +675,57 @@ static void smc_fback_forward_wakeup(struct smc_sock *smc, struct sock *clcsk,

static void smc_fback_state_change(struct sock *clcsk)
{
- struct smc_sock *smc =
- smc_clcsock_user_data(clcsk);
+ struct smc_sock *smc;

- if (!smc)
- return;
- smc_fback_forward_wakeup(smc, clcsk, smc->clcsk_state_change);
+ read_lock_bh(&clcsk->sk_callback_lock);
+ smc = smc_clcsock_user_data(clcsk);
+ if (smc)
+ smc_fback_forward_wakeup(smc, clcsk,
+ smc->clcsk_state_change);
+ read_unlock_bh(&clcsk->sk_callback_lock);
}

static void smc_fback_data_ready(struct sock *clcsk)
{
- struct smc_sock *smc =
- smc_clcsock_user_data(clcsk);
+ struct smc_sock *smc;

- if (!smc)
- return;
- smc_fback_forward_wakeup(smc, clcsk, smc->clcsk_data_ready);
+ read_lock_bh(&clcsk->sk_callback_lock);
+ smc = smc_clcsock_user_data(clcsk);
+ if (smc)
+ smc_fback_forward_wakeup(smc, clcsk,
+ smc->clcsk_data_ready);
+ read_unlock_bh(&clcsk->sk_callback_lock);
}

static void smc_fback_write_space(struct sock *clcsk)
{
- struct smc_sock *smc =
- smc_clcsock_user_data(clcsk);
+ struct smc_sock *smc;

- if (!smc)
- return;
- smc_fback_forward_wakeup(smc, clcsk, smc->clcsk_write_space);
+ read_lock_bh(&clcsk->sk_callback_lock);
+ smc = smc_clcsock_user_data(clcsk);
+ if (smc)
+ smc_fback_forward_wakeup(smc, clcsk,
+ smc->clcsk_write_space);
+ read_unlock_bh(&clcsk->sk_callback_lock);
}

static void smc_fback_error_report(struct sock *clcsk)
{
- struct smc_sock *smc =
- smc_clcsock_user_data(clcsk);
+ struct smc_sock *smc;

- if (!smc)
- return;
- smc_fback_forward_wakeup(smc, clcsk, smc->clcsk_error_report);
+ read_lock_bh(&clcsk->sk_callback_lock);
+ smc = smc_clcsock_user_data(clcsk);
+ if (smc)
+ smc_fback_forward_wakeup(smc, clcsk,
+ smc->clcsk_error_report);
+ read_unlock_bh(&clcsk->sk_callback_lock);
}

static void smc_fback_replace_callbacks(struct smc_sock *smc)
{
struct sock *clcsk = smc->clcsock->sk;

+ write_lock_bh(&clcsk->sk_callback_lock);
clcsk->sk_user_data = (void *)((uintptr_t)smc | SK_USER_DATA_NOCOPY);

smc_clcsock_replace_cb(&clcsk->sk_state_change, smc_fback_state_change,
@@ -711,6 +736,8 @@ static void smc_fback_replace_callbacks(struct smc_sock *smc)
&smc->clcsk_write_space);
smc_clcsock_replace_cb(&clcsk->sk_error_report, smc_fback_error_report,
&smc->clcsk_error_report);
+
+ write_unlock_bh(&clcsk->sk_callback_lock);
}

static int smc_switch_to_fallback(struct smc_sock *smc, int reason_code)
@@ -2095,17 +2122,20 @@ static void smc_tcp_listen_work(struct work_struct *work)

static void smc_clcsock_data_ready(struct sock *listen_clcsock)
{
- struct smc_sock *lsmc =
- smc_clcsock_user_data(listen_clcsock);
+ struct smc_sock *lsmc;

+ read_lock_bh(&listen_clcsock->sk_callback_lock);
+ lsmc = smc_clcsock_user_data(listen_clcsock);
if (!lsmc)
- return;
+ goto out;
lsmc->clcsk_data_ready(listen_clcsock);
if (lsmc->sk.sk_state == SMC_LISTEN) {
sock_hold(&lsmc->sk); /* sock_put in smc_tcp_listen_work() */
if (!queue_work(smc_hs_wq, &lsmc->tcp_listen_work))
sock_put(&lsmc->sk);
}
+out:
+ read_unlock_bh(&listen_clcsock->sk_callback_lock);
}

static int smc_listen(struct socket *sock, int backlog)
@@ -2137,10 +2167,12 @@ static int smc_listen(struct socket *sock, int backlog)
/* save original sk_data_ready function and establish
* smc-specific sk_data_ready function
*/
+ write_lock_bh(&smc->clcsock->sk->sk_callback_lock);
smc->clcsock->sk->sk_user_data =
(void *)((uintptr_t)smc | SK_USER_DATA_NOCOPY);
smc_clcsock_replace_cb(&smc->clcsock->sk->sk_data_ready,
smc_clcsock_data_ready, &smc->clcsk_data_ready);
+ write_unlock_bh(&smc->clcsock->sk->sk_callback_lock);

/* save original ops */
smc->ori_af_ops = inet_csk(smc->clcsock->sk)->icsk_af_ops;
@@ -2152,9 +2184,11 @@ static int smc_listen(struct socket *sock, int backlog)

rc = kernel_listen(smc->clcsock, backlog);
if (rc) {
+ write_lock_bh(&smc->clcsock->sk->sk_callback_lock);
smc_clcsock_restore_cb(&smc->clcsock->sk->sk_data_ready,
&smc->clcsk_data_ready);
smc->clcsock->sk->sk_user_data = NULL;
+ write_unlock_bh(&smc->clcsock->sk->sk_callback_lock);
goto out;
}
sk->sk_max_ack_backlog = backlog;
diff --git a/net/smc/smc_close.c b/net/smc/smc_close.c
index 42f9a7cf9e671..313ef522dfab4 100644
--- a/net/smc/smc_close.c
+++ b/net/smc/smc_close.c
@@ -212,9 +212,11 @@ int smc_close_active(struct smc_sock *smc)
sk->sk_state = SMC_CLOSED;
sk->sk_state_change(sk); /* wake up accept */
if (smc->clcsock && smc->clcsock->sk) {
+ write_lock_bh(&smc->clcsock->sk->sk_callback_lock);
smc_clcsock_restore_cb(&smc->clcsock->sk->sk_data_ready,
&smc->clcsk_data_ready);
smc->clcsock->sk->sk_user_data = NULL;
+ write_unlock_bh(&smc->clcsock->sk->sk_callback_lock);
rc = kernel_sock_shutdown(smc->clcsock, SHUT_RDWR);
}
smc_close_cleanup_listen(sk);
--
2.51.0