From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8FBC0260566 for ; Fri, 24 Apr 2026 13:51:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777038698; cv=none; b=rWCDQ3EonT7PuY997lTt54gggNTqHg6PaUrM8bjDrwHfhh24CEd7L9qB0OuJE8wn/6b1vhhbCwHRi1hXv9oSHZdQJL+LDpQ3xwX1iOEPBp8hU53FhBDoFAg0ZZJJ2Iy6QbHQVkE5zLJ6LfuztGuFi2GC+4HgbYe2322C2NlGsCo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777038698; c=relaxed/simple; bh=yzINWC19jxPLkfn8qZZapo/RqhMspLiP/J0J4Xx0n24=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=K0Qxtf826TZM8OWBE0WNIg+3kVmvJivDuO1UO3z6u1ufcEULvrN+nv8Cmq/HuRa6C0W/EFvuz1GajFnj8Qg8N5Ketb02W/mBWxKHU0o9IkJhdx22pd0CwJhgXbRCeGFHf3PlPSq0gdEK2yFEXSrd5TlstKB/ub0QvLkx4h2zlD4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SssMPKqc; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="SssMPKqc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D5E5FC19425; Fri, 24 Apr 2026 13:51:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777038698; bh=yzINWC19jxPLkfn8qZZapo/RqhMspLiP/J0J4Xx0n24=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SssMPKqc5oVy2QgVoHd0eY751NeVgf33ffZUoeMhe7t7GqC2qmhmjD7cgo8XZ190+ 4RHpTSqS2xEzOqP3Oq3XX7NAJgCmRYSdurbYkylQrLgB+6pB6//1xsXm/QSZ1Y29Os /G1Su3WgApGCe9M6AXHAPJkhH+57WGNXwKvpiAGta8DAH2UgT/Yw4C5bHao0zqCGGV Eh6njLvfXIQud4WXtZ21aBSqRZkmdNhYGoPJay8tYoD+7n1ag3z8F0/QamoFK8itUO A01huOjVbGITf2dCpRy87CKvWMEnI7gB1JhYvYiullLVld5UWqAF3DBDnFqNO+G/KB BPFBsM25NzKLQ== From: Sasha Levin To: stable@vger.kernel.org Cc: Michael Bommarito , Namjae Jeon , Steve French , Sasha Levin Subject: [PATCH 5.15.y] smb: server: fix active_num_conn leak on transport allocation failure Date: Fri, 24 Apr 2026 09:51:35 -0400 Message-ID: <20260424135135.2085884-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026042442-saggy-bucktooth-2b96@gregkh> References: <2026042442-saggy-bucktooth-2b96@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Michael Bommarito [ Upstream commit 6551300dc452ac16a855a83dbd1e74899542d3b3 ] Commit 77ffbcac4e56 ("smb: server: fix leak of active_num_conn in ksmbd_tcp_new_connection()") addressed the kthread_run() failure path. The earlier alloc_transport() == NULL path in the same function has the same leak, is reachable pre-authentication via any TCP connect to port 445, and was empirically reproduced on UML (ARCH=um, v7.0-rc7): a small number of forced allocation failures were sufficient to put ksmbd into a state where every subsequent connection attempt was rejected for the remainder of the boot. ksmbd_kthread_fn() increments active_num_conn before calling ksmbd_tcp_new_connection() and discards the return value, so when alloc_transport() returns NULL the socket is released and -ENOMEM returned without decrementing the counter. Each such failure permanently consumes one slot from the max_connections pool; once cumulative failures reach the cap, atomic_inc_return() hits the threshold on every subsequent accept and every new connection is rejected. The counter is only reset by module reload. An unauthenticated remote attacker can drive the server toward the memory pressure that makes alloc_transport() fail by holding open connections with large RFC1002 lengths up to MAX_STREAM_PROT_LEN (0x00FFFFFF); natural transient allocation failures on a loaded host produce the same drift more slowly. Mirror the existing rollback pattern in ksmbd_kthread_fn(): on the alloc_transport() failure path, decrement active_num_conn gated on server_conf.max_connections. Repro details: with the patch reverted, forced alloc_transport() NULL returns leaked counter slots and subsequent connection attempts -- including legitimate connects issued after the forced-fail window had closed -- were all rejected with "Limit the maximum number of connections". With this patch applied, the same connect sequence produces no rejections and the counter cycles cleanly between zero and one on every accept. Fixes: 0d0d4680db22 ("ksmbd: add max connections parameter") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-6 Assisted-by: Codex:gpt-5-4 Signed-off-by: Michael Bommarito Acked-by: Namjae Jeon Signed-off-by: Steve French Signed-off-by: Sasha Levin --- fs/ksmbd/transport_tcp.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/ksmbd/transport_tcp.c b/fs/ksmbd/transport_tcp.c index 7ef201b7ddb57..b9ff22e6f4db4 100644 --- a/fs/ksmbd/transport_tcp.c +++ b/fs/ksmbd/transport_tcp.c @@ -191,6 +191,8 @@ static int ksmbd_tcp_new_connection(struct socket *client_sk) t = alloc_transport(client_sk); if (!t) { sock_release(client_sk); + if (server_conf.max_connections) + atomic_dec(&active_num_conn); return -ENOMEM; } -- 2.53.0