[PATCH 6.1 042/312] net/smc: fix double-free of smc_spd_priv when tee() duplicates splice pipe buffer

Greg Kroah-Hartman
2026-04-08T18:08:42Z

From: Qi Tang <tpluszz77@gmail.com>

[ Upstream commit 24dd586bb4cbba1889a50abe74143817a095c1c9 ]

smc_rx_splice() allocates one smc_spd_priv per pipe_buffer and stores
the pointer in pipe_buffer.private. The pipe_buf_operations for these
buffers used .get = generic_pipe_buf_get, which only increments the page
reference count when tee(2) duplicates a pipe buffer. The smc_spd_priv
pointer itself was not handled, so after tee() both the original and the
cloned pipe_buffer share the same smc_spd_priv *.

When both pipes are subsequently released, smc_rx_pipe_buf_release() is
called twice against the same object:

1st call: kfree(priv) sock_put(sk) smc_rx_update_cons() [correct]
2nd call: kfree(priv) sock_put(sk) smc_rx_update_cons() [UAF]

KASAN reports a slab-use-after-free in smc_rx_pipe_buf_release(), which
then escalates to a NULL-pointer dereference and kernel panic via
smc_rx_update_consumer() when it chases the freed priv->smc pointer:

BUG: KASAN: slab-use-after-free in smc_rx_pipe_buf_release+0x78/0x2a0
Read of size 8 at addr ffff888004a45740 by task smc_splice_tee_/74
Call Trace:
<TASK>
dump_stack_lvl+0x53/0x70
print_report+0xce/0x650
kasan_report+0xc6/0x100
smc_rx_pipe_buf_release+0x78/0x2a0
free_pipe_info+0xd4/0x130
pipe_release+0x142/0x160
__fput+0x1c6/0x490
__x64_sys_close+0x4f/0x90
do_syscall_64+0xa6/0x1a0
entry_SYSCALL_64_after_hwframe+0x77/0x7f
</TASK>

BUG: kernel NULL pointer dereference, address: 0000000000000020
RIP: 0010:smc_rx_update_consumer+0x8d/0x350
Call Trace:
<TASK>
smc_rx_pipe_buf_release+0x121/0x2a0
free_pipe_info+0xd4/0x130
pipe_release+0x142/0x160
__fput+0x1c6/0x490
__x64_sys_close+0x4f/0x90
do_syscall_64+0xa6/0x1a0
entry_SYSCALL_64_after_hwframe+0x77/0x7f
</TASK>
Kernel panic - not syncing: Fatal exception

Beyond the memory-safety problem, duplicating an SMC splice buffer is
semantically questionable: smc_rx_update_cons() would advance the
consumer cursor twice for the same data, corrupting receive-window
accounting. A refcount on smc_spd_priv could fix the double-free, but
the cursor-accounting issue would still need to be addressed separately.

The .get callback is invoked by both tee(2) and splice_pipe_to_pipe()
for partial transfers; both will now return -EFAULT. Users who need
to duplicate SMC socket data must use a copy-based read path.

Fixes: 9014db202cb7 ("smc: add support for splice()")
Signed-off-by: Qi Tang <tpluszz77@gmail.com>
Link: https://patch.msgid.link/20260318064847.23341-1-tpluszz77@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/smc/smc_rx.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/net/smc/smc_rx.c b/net/smc/smc_rx.c
index e57002d2ac372..8f838ddeaafe8 100644
--- a/net/smc/smc_rx.c
+++ b/net/smc/smc_rx.c
@@ -131,9 +131,16 @@ static void smc_rx_pipe_buf_release(struct pipe_inode_info *pipe,
sock_put(sk);
}

+static bool smc_rx_pipe_buf_get(struct pipe_inode_info *pipe,
+ struct pipe_buffer *buf)
+{
+ /* smc_spd_priv in buf->private is not shareable; disallow cloning. */
+ return false;
+}
+
static const struct pipe_buf_operations smc_pipe_ops = {
.release = smc_rx_pipe_buf_release,
- .get = generic_pipe_buf_get
+ .get = smc_rx_pipe_buf_get,
};

static void smc_rx_spd_release(struct splice_pipe_desc *spd,
--
2.51.0