From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793847711; b=SMXxftmlONjaOc19OzIGmuQ2zP0YzPV0aDcN/e256FBQ+qiOdi3MKHMvfu5T4M1P44Xf IX/GHiS7mqbljtgNxylk0aP9z2igAP48mSq9CAD7AGzk5ZjhlOJsIxvk9i3TWGk0/sUNd mkYrXP9UDcLnL7CC5K2MMqTFwrIpAQ/oZl2afGEsfIeFJpGaUbWsZolZumut9bgGAAbTD mT02z0TDXWUo9qUBrQA30oSKs1JZqRiXG18MM4J/d1ubGYH5q2Ga1IsMt6jJB0bsjycEF LNzZGs0lJ9kmWkkNSyLAzP2JWiGSbzaDPE/cW9ALVmw4TfjUihViSrHFJtGHbR8oFuw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793847711; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=xNUucnfc+vfRoGbQhXqn2kYs4MzqO1lstHiwfwPXjRw=; b=jwfDMDpZqPd6kJy5paeBVpqYbkpaB/ZD5Pq+OCNWmsjrH5/H4GPT3nfnHGpiX0OrhQOc j2LkiLRV2rj4HlMhIi/PbVsM/uhsHhxVnEuMXj1VdSHYb3f+rTOBDYrr9EEIqYX4TJEvw 9dq+wlXO5lgpULa6kmTUdHiZTGx6JkLdmyRFf0t39QSYlwsBSGThEkxUcKSOr5VUlboJv d9uIgw3iXF4YY2DU98Bdje4EjnDVdipKJ9SOwWufAa3jrE2VPXi9nHnB02GigSluHBxjk mLjJBzi1BrO5TwQF0gLOGpaa0By7eBnwWqgArShAoK7HZbpxxPS3mTua8PsoIQKLpiQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b="msF/fk7H"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 277D6606A32D for ; Thu, 5 Nov 2026 03:01:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=msF/fk7H Received: by smtp.kernel.org (Postfix) with ESMTPSA id E4A401F00919; Thu, 5 Nov 2026 03:01:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793847710; bh=xNUucnfc+vfRoGbQhXqn2kYs4MzqO1lstHiwfwPXjRw=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=msF/fk7HsqHYGObzvqZdUMgQHlRR/Ch4uf7mZAO8vmRc3q+ZB88ChA5WYKAniK1lg WUE0wL2O92lynSnt/guZe81e/CJFOzmAiBqAkl3WFCpKLQWKB2M//UrCbQWBbR/4sE QcOvXdFjLzfT6evJg24Svn+I230Usg6GpNIHYW9CkUwLW37duwVsfnuC5Tkg6ggCeO BVLaxQmI8jPMoKKsF7cdYK7p4d+Cy3ZlusAVdYveIXlZpeYW+A08+hQn+Dxy8KKT9g sEF8To1/TsoMbHS+hJSx9t9zbu9oYXZ3yOFpv6Njs95txuX7h4IYpzUkYpAsp5MpfG wqoVJkKXPgsMQ== From: Sasha Levin To: stable@vger.kernel.org Cc: Eduard Zateev , syzbot+5c3ed2a0de3270efc921@syzkaller.appspotmail.com, syzbot+c2ec61adfbcb24e5ec20@syzkaller.appspotmail.com, Michail Andreas Michalopoulos , Paulo Alcantara , Sasha Levin Subject: [PATCH 6.12.y] smb: client: hold server info until cifsd exits Date: Wed, 4 Nov 2026 22:01:48 -0500 Message-ID: <20261105030125.1213408-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026110420-crunching-excess-eb90@gregkh> References: <2026110420-crunching-excess-eb90@gregkh> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Eduard Zateev [ Upstream commit 482c117c6dbeee382790168af10959810450ab09 ] The last session reference can be dropped while the cifsd demultiplex thread is still running clean_demultiplex_info(). That thread frees TCP_Server_Info there, racing with cifs_put_tcp_session() as it releases the server crypto state. syzbot reported a KASAN use-after-free in cifs_crypto_secmech_release(). Keep an object reference for the cifsd thread. Defer final crypto, session-key, network namespace, string, and structure cleanup until both the last session reference and the thread reference are dropped. Drop the thread reference after clean_demultiplex_info() has finished using the server. Build-tested with ARCH=arm64 and W=1 for fs/smb/client/connect.o. The KASAN reproducer was not run on the patched kernel. Fixes: a5c3e1c725af ("Revert "cifs: No need to send SIGKILL to demux_thread during umount"") Reported-by: syzbot+5c3ed2a0de3270efc921@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=5c3ed2a0de3270efc921 Reported-by: syzbot+c2ec61adfbcb24e5ec20@syzkaller.appspotmail.com Closes: https://syzbot.org/bug?extid=c2ec61adfbcb24e5ec20 Assisted-by: LLM OpenAI Codex Signed-off-by: Eduard Zateev Cc: stable@vger.kernel.org Tested-by: Michail Andreas Michalopoulos Signed-off-by: Paulo Alcantara [ sashal: Adjusted patch context for missing NetBIOS fields and existing kfree() cleanup instead of kfree_sensitive(). ] Signed-off-by: Sasha Levin --- fs/smb/client/cifsglob.h | 2 ++ fs/smb/client/connect.c | 33 +++++++++++++++++++++------------ 2 files changed, 23 insertions(+), 12 deletions(-) diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h index f5ca2cd653e95..8ffc8b2ab6db4 100644 --- a/fs/smb/client/cifsglob.h +++ b/fs/smb/client/cifsglob.h @@ -16,6 +16,7 @@ #include #include #include +#include #include #include #include @@ -647,6 +648,7 @@ struct TCP_Server_Info { spinlock_t srv_lock; /* protect anything here that is not protected */ __u64 conn_id; /* connection identifier (useful for debugging) */ int srv_count; /* reference counter */ + refcount_t obj_refs; /* struct lifetime: srv_count users + cifsd */ /* 15 character server name + 0x20 16th byte indicating type = srv */ char server_RFC1001_name[RFC1001_NAME_LEN_WITH_NULL]; struct smb_version_operations *ops; diff --git a/fs/smb/client/connect.c b/fs/smb/client/connect.c index 81961a54c9f1c..225bcd149a32f 100644 --- a/fs/smb/client/connect.c +++ b/fs/smb/client/connect.c @@ -977,6 +977,19 @@ cifs_enable_signing(struct TCP_Server_Info *server, bool mnt_sign_required) return 0; } +static void cifs_tcp_server_put(struct TCP_Server_Info *server) +{ + if (!refcount_dec_and_test(&server->obj_refs)) + return; + + cifs_crypto_secmech_release(server); + kfree_sensitive(server->session_key.response); + put_net(cifs_net_ns(server)); + kfree(server->leaf_fullpath); + kfree(server->hostname); + kfree_sensitive(server); +} + static noinline_for_stack void clean_demultiplex_info(struct TCP_Server_Info *server) { @@ -1062,14 +1075,11 @@ clean_demultiplex_info(struct TCP_Server_Info *server) */ } - put_net(cifs_net_ns(server)); - kfree(server->leaf_fullpath); - kfree(server->hostname); - kfree(server); - length = atomic_dec_return(&tcpSesAllocCount); if (length > 0) mempool_resize(cifs_req_poolp, length + cifs_min_rcv); + + cifs_tcp_server_put(server); } static int @@ -1678,7 +1688,7 @@ cifs_put_tcp_session(struct TCP_Server_Info *server, int from_reconnect) else cancel_delayed_work_sync(&server->reconnect); - /* For secondary channels, we pick up ref-count on the primary server */ + /* For secondary channels, drop the reference on the primary server */ if (SERVER_IS_CHAN(server)) cifs_put_tcp_session(server->primary_server, from_reconnect); @@ -1686,15 +1696,11 @@ cifs_put_tcp_session(struct TCP_Server_Info *server, int from_reconnect) server->tcpStatus = CifsExiting; spin_unlock(&server->srv_lock); - cifs_crypto_secmech_release(server); - - kfree_sensitive(server->session_key.response); - server->session_key.response = NULL; - server->session_key.len = 0; - task = xchg(&server->tsk, NULL); if (task) send_sig(SIGKILL, task, 1); + + cifs_tcp_server_put(server); } struct TCP_Server_Info * @@ -1716,6 +1722,7 @@ cifs_get_tcp_session(struct smb3_fs_context *ctx, rc = -ENOMEM; goto out_err; } + refcount_set(&tcp_ses->obj_refs, 1); tcp_ses->hostname = kstrdup(ctx->server_hostname, GFP_KERNEL); if (!tcp_ses->hostname) { @@ -1856,6 +1863,8 @@ cifs_get_tcp_session(struct smb3_fs_context *ctx, module_put(THIS_MODULE); goto out_err_crypto_release; } + /* Keep the server alive until the demultiplex thread has exited */ + refcount_inc(&tcp_ses->obj_refs); /* thread created, put it on the list */ spin_lock(&cifs_tcp_ses_lock); list_add(&tcp_ses->tcp_ses_list, &cifs_tcp_ses_list); -- 2.53.0