From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Vega <vega@nebusec.ai>,
	Xiao Liu <lx24@stu.ynu.edu.cn>,
	Daming Li <d4n.for.sec@gmail.com>,
	Ren Wei <enjou1224z@gmail.com>,
	Dust Li <dust.li@linux.alibaba.com>,
	Sidraya Jayagond <sidraya@linux.ibm.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.15 256/272] net: smc: fix splice entry lifetime imbalance in smc_rx_splice
Date: Thu, 20 Aug 2026 16:57:20 +0200
Message-ID: <20260820145239.312323792@linuxfoundation.org>
In-Reply-To: <20260820145231.229664293@linuxfoundation.org>
References: <20260820145231.229664293@linuxfoundation.org>
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5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daming Li <d4n.for.sec@gmail.com>

commit 5d9686af2976741bbd79b150d1c9e60b81e7f12e upstream.

smc_rx_splice() passes pages to splice_to_pipe() before taking the
references that cover the lifetime of each splice entry. In the
VM-backed RMB path, splice_to_pipe() may drop unqueued entries through
smc_rx_spd_release(), while queued entries are released later via the
pipe buffer callback.

The old post-splice accounting also derives the number of queued VM pages
from an offset mutated while building the descriptor, and a multi-page
splice pairs one sock_hold() with multiple sock_put() calls.

Take the page and socket references for every candidate entry before
splice_to_pipe(), and drop the matching private state, page reference,
and socket reference from smc_rx_spd_release() for entries that never
get queued. This fixes a refcount imbalance that can underflow page
refcounts and trigger a use-after-free.

Fixes: 9014db202cb7 ("smc: add support for splice()")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Co-developed-by: Xiao Liu <lx24@stu.ynu.edu.cn>
Signed-off-by: Xiao Liu <lx24@stu.ynu.edu.cn>
Signed-off-by: Daming Li <d4n.for.sec@gmail.com>
Signed-off-by: Ren Wei <enjou1224z@gmail.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Reviewed-by: Sidraya Jayagond <sidraya@linux.ibm.com>
Link: https://patch.msgid.link/20260730145552.360287-2-enjou1224z@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ collapsed the multi-page get_page()/sock_hold() loop to a single get_page()/sock_hold() pair and dropped the trailing kfree() calls, as 5.15 lacks the multi-page pages[]/partial[]/priv[] arrays ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/smc/smc_rx.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- a/net/smc/smc_rx.c
+++ b/net/smc/smc_rx.c
@@ -145,7 +145,12 @@ static const struct pipe_buf_operations
 static void smc_rx_spd_release(struct splice_pipe_desc *spd,
 			       unsigned int i)
 {
+	struct smc_spd_priv *priv = (struct smc_spd_priv *)spd->partial[i].private;
+	struct sock *sk = &priv->smc->sk;
+
+	kfree(priv);
 	put_page(spd->pages[i]);
+	sock_put(sk);
 }
 
 static int smc_rx_splice(struct pipe_inode_info *pipe, char *src, size_t len,
@@ -165,6 +170,8 @@ static int smc_rx_splice(struct pipe_ino
 	partial.len = len;
 	partial.private = (unsigned long)priv;
 
+	get_page(smc->conn.rmb_desc->pages);
+	sock_hold(&smc->sk);
 	spd.nr_pages_max = 1;
 	spd.nr_pages = 1;
 	spd.pages = &smc->conn.rmb_desc->pages;
@@ -173,11 +180,8 @@ static int smc_rx_splice(struct pipe_ino
 	spd.spd_release = smc_rx_spd_release;
 
 	bytes = splice_to_pipe(pipe, &spd);
-	if (bytes > 0) {
-		sock_hold(&smc->sk);
-		get_page(smc->conn.rmb_desc->pages);
+	if (bytes > 0)
 		atomic_add(bytes, &smc->conn.splice_pending);
-	}
 
 	return bytes;
 }