From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Mahanta Jambigi <mjambigi@linux.ibm.com>,
	Sidraya Jayagond <sidraya@linux.ibm.com>,
	Breno Leitao <leitao@debian.org>,
	Dust Li <dust.li@linux.alibaba.com>,
	Paolo Abeni <pabeni@redhat.com>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.18 096/250] net/smc: fix TOCTOU race between smc_listen_out() and listener close
Date: Mon, 17 Aug 2026 15:30:57 +0200
Message-ID: <20260817132540.435367279@linuxfoundation.org>
In-Reply-To: <20260817132536.466235697@linuxfoundation.org>
References: <20260817132536.466235697@linuxfoundation.org>
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6.18-stable review patch.  If anyone has any objections, please let me know.

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

From: Sidraya Jayagond <sidraya@linux.ibm.com>

[ Upstream commit 185a4caeecabc150106deda1da170b09f2ad803f ]

smc_listen_out() reads lsmc->sk.sk_state without the listener lock,
then acquires lock_sock_nested() only after the check passes. This
opens a window where smc_close_active() can transition the listener
to SMC_CLOSED, call smc_close_cleanup_listen() to drain the accept
queue, and release the lock, all between the lockless read and the
delayed lock acquisition:

  smc_listen_work (smc_hs_wq)          smc_close_active()
  -------------------------------      -------------------------
  release_sock(child)
  if (sk_state == SMC_LISTEN) TRUE
                                        lock_sock(listener)
                                        sk_state = SMC_CLOSED
                                        smc_close_cleanup_listen()
                                        release_sock(listener)
                                        flush_work(tcp_listen_work)
  lock_sock_nested(listener)
  smc_accept_enqueue(listener, child) /* child enqueued on dead listener */

smc_close_active() flushes only tcp_listen_work. Work items already
dispatched onto smc_hs_wq for the CLC handshake continue running
unguarded. smc_accept_enqueue() takes a sock_hold() on the child that
is never released, so the child smc_sock, its clcsock, and the
reference all leak. A remote peer that opens TCP connections while the
server calls close() can exhaust kernel memory.

Move lock_sock_nested() to before the sk_state check so that the test
and the enqueue are atomic under the listener lock.

Fixes: fd57770dd198 ("net/smc: wait for pending work before clcsock release_sock")
Reviewed-by: Mahanta Jambigi <mjambigi@linux.ibm.com>
Signed-off-by: Sidraya Jayagond <sidraya@linux.ibm.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Link: https://patch.msgid.link/20260803070701.126339-1-sidraya@linux.ibm.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/smc/af_smc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 47963eda478f6..bc7b4a33b7261 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -1935,11 +1935,12 @@ static void smc_listen_out(struct smc_sock *new_smc)
 		atomic_dec(&lsmc->queued_smc_hs);
 
 	release_sock(newsmcsk); /* lock in smc_listen_work() */
+	lock_sock_nested(&lsmc->sk, SINGLE_DEPTH_NESTING);
 	if (lsmc->sk.sk_state == SMC_LISTEN) {
-		lock_sock_nested(&lsmc->sk, SINGLE_DEPTH_NESTING);
 		smc_accept_enqueue(&lsmc->sk, newsmcsk);
 		release_sock(&lsmc->sk);
 	} else { /* no longer listening */
+		release_sock(&lsmc->sk);
 		smc_close_non_accepted(newsmcsk);
 	}
 
-- 
2.53.0