From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id CFE4549B1F8; Tue, 1 Sep 2026 18:21:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788286918; cv=none; b=iAqV1QeXfjz81e+15JGidU7zjjK3LMmupZFqUkqMJJdwPqtM1c7a2jSnzCLTFkLscwmTL3ydP3zPXQBki35mXc+rf2z/7+o2yr+lR9d+zL3swGKE8MjwpI85o9F0M3EjSaX79daEP6cFpnxns4GZopFeXuvixswiTFxDPNcVjKE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788286918; c=relaxed/simple; bh=qcbqwjo8PQ6HOaFe+HESTBjYFEM7Qgci90O8hxG6YPo=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=NVcRlfJs1vzRLhvns68R1D7zI0jStvWIkz6beFFYHXi1xCcMdp7YuLNcBfosB54+sLXaPD1YTmMOICQV2qrli7AESLoeGO1wR1lN1+JhHvr80kPSJPfyUscnnjz6B35Wa5lxf4WpFNxKz43NHu+ACMhPjGTP7Vux6WAx4XW6JnI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=pP1dPX9x; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="pP1dPX9x" Received: from localhost.localdomain (unknown [52.172.102.219]) by linux.microsoft.com (Postfix) with ESMTPSA id 4993E20B7166; Tue, 1 Sep 2026 11:21:10 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 4993E20B7166 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1788286880; bh=j8p0fHYDQhDNXEvnAW4cKjXCyIpdjeOjWC3CDthUOCI=; h=From:To:Cc:Subject:Date:From; b=pP1dPX9xSEtbkNo1feR0YamEim4twVmOSp3MMncT84klmhFJ361Z+m/HWkY3EZI0C PiDXdO4tSifA4gQibyRa0ilQS5FLI+bMZZJzMKbatsrr4GtEyd0y7Nv75pidixxk36 awCu+lfk9Tg5HMLrwcDSM5iODkqAMPKzGnxm85Qk= From: "Cen Zhang (Microsoft Security FORGE Labs)" To: linkinjeon@kernel.org, smfrench@gmail.com Cc: senozhatsky@chromium.org, tom@talpey.com, chenxiaosong@chenxiaosong.com, nicholas@carlini.com, bahubali.bg@samsung.com, kees@kernel.org, linux-cifs@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, AutonomousCodeSecurity@microsoft.com, xmei5@asu.edu, tgopinath@linux.microsoft.com, kys@microsoft.com, "Cen Zhang (Microsoft Security FORGE Labs)" Subject: [PATCH] ksmbd: fix tree connection use-after-free in smb2_tree_connect() Date: Tue, 1 Sep 2026 14:21:36 -0400 Message-ID: <20260901182136.13745-1-cenzhang@linux.microsoft.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-cifs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit ksmbd_tree_conn_connect() publishes a new tree connection in sess->tree_conns with a single reference and returns its pointer to smb2_tree_connect(). The handler continues to initialize the object and build the response after publication. A concurrent session logoff can erase the connection and drop that reference, freeing the object while the handler still uses it. BUG: KASAN: slab-use-after-free in smb2_tree_connect+0xe3d/0xf90 smb2_tree_connect (fs/smb/server/smb2pdu.c:2872) handle_ksmbd_work process_one_work worker_thread kthread After xa_store() succeeds, take a second reference before releasing tree_conns_lock. The original reference belongs to the xarray entry and the second belongs to the creating smb2_tree_connect() handler. Keep the references balanced in every path: - On normal exit or an error after publication, smb2_tree_connect() drops its creator reference. Error cleanup also calls ksmbd_tree_conn_disconnect(), which drops the xarray reference only if it removes the exact entry. - SMB2 TREE_DISCONNECT uses the same helper to remove the entry and drop its xarray reference. The request's existing lookup reference remains owned by the request and is released by the existing cleanup. - Session LOGOFF removes each entry and drops its xarray reference. If it wins the race, later cleanup sees that the entry is gone and does not drop that reference again. To enforce this ownership, claim the disconnected state and erase the exact entry atomically under tree_conns_lock. This guarantees one drop for the xarray reference and one drop by each in-flight user, regardless of which teardown path wins. If logoff removes the entry before initialization completes, fail the connect instead of marking the detached object TREE_CONNECTED. Fixes: 33b235a6e6eb ("ksmbd: fix race condition between tree conn lookup and disconnect") Reported-by: Xiang Mei (Microsoft) Cc: AutonomousCodeSecurity@microsoft.com Cc: stable@vger.kernel.org Signed-off-by: Cen Zhang (Microsoft Security FORGE Labs) --- fs/smb/server/mgmt/tree_connect.c | 8 ++++++++ fs/smb/server/smb2pdu.c | 28 +++++++++++++--------------- 2 files changed, 21 insertions(+), 15 deletions(-) diff --git a/fs/smb/server/mgmt/tree_connect.c b/fs/smb/server/mgmt/tree_connect.c index 5f63e236267a..dd1db3554cae 100644 --- a/fs/smb/server/mgmt/tree_connect.c +++ b/fs/smb/server/mgmt/tree_connect.c @@ -82,6 +82,8 @@ ksmbd_tree_conn_connect(struct ksmbd_work *work, const char *share_name) down_write(&sess->tree_conns_lock); ret = xa_err(xa_store(&sess->tree_conns, tree_conn->id, tree_conn, KSMBD_DEFAULT_GFP)); + if (!ret) + atomic_inc(&tree_conn->refcount); up_write(&sess->tree_conns_lock); if (ret) { status.ret = -ENOMEM; @@ -129,6 +131,12 @@ int ksmbd_tree_conn_disconnect(struct ksmbd_session *sess, struct ksmbd_tree_connect *tree_conn) { down_write(&sess->tree_conns_lock); + if (tree_conn->t_state == TREE_DISCONNECTED || + xa_load(&sess->tree_conns, tree_conn->id) != tree_conn) { + up_write(&sess->tree_conns_lock); + return -ENOENT; + } + tree_conn->t_state = TREE_DISCONNECTED; xa_erase(&sess->tree_conns, tree_conn->id); up_write(&sess->tree_conns_lock); diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c index 903ffffdd187..e7c965e7b068 100644 --- a/fs/smb/server/smb2pdu.c +++ b/fs/smb/server/smb2pdu.c @@ -2804,6 +2804,7 @@ int smb2_tree_connect(struct ksmbd_work *work) struct ksmbd_session *sess = work->sess; char *treename = NULL, *name = NULL; struct ksmbd_tree_conn_status status; + struct ksmbd_tree_connect *tree_conn = NULL; struct ksmbd_share_config *share = NULL; int rc = -EINVAL; @@ -2831,6 +2832,7 @@ int smb2_tree_connect(struct ksmbd_work *work) status = ksmbd_tree_conn_connect(work, name); if (status.ret == KSMBD_TREE_CONN_STATUS_OK) { + tree_conn = status.tree_conn; rsp->hdr.Id.SyncId.TreeId = cpu_to_le32(status.tree_conn->id); share = status.tree_conn->share_conf; @@ -2874,8 +2876,15 @@ int smb2_tree_connect(struct ksmbd_work *work) status.tree_conn->posix_extensions = true; down_write(&sess->tree_conns_lock); - status.tree_conn->t_state = TREE_CONNECTED; + if (status.tree_conn->t_state == TREE_DISCONNECTED) { + status.ret = KSMBD_TREE_CONN_STATUS_ERROR; + share = NULL; + } else { + status.tree_conn->t_state = TREE_CONNECTED; + } up_write(&sess->tree_conns_lock); + if (status.ret != KSMBD_TREE_CONN_STATUS_OK) + goto out_err1; rsp->StructureSize = cpu_to_le16(16); out_err1: /* @@ -2902,9 +2911,6 @@ int smb2_tree_connect(struct ksmbd_work *work) rc = ksmbd_iov_pin_rsp(work, rsp, sizeof(struct smb2_tree_connect_rsp)); if (rc) { if (status.ret == KSMBD_TREE_CONN_STATUS_OK) { - down_write(&sess->tree_conns_lock); - status.tree_conn->t_state = TREE_DISCONNECTED; - up_write(&sess->tree_conns_lock); ksmbd_tree_conn_disconnect(sess, status.tree_conn); status.tree_conn = NULL; } @@ -2945,6 +2951,9 @@ int smb2_tree_connect(struct ksmbd_work *work) if (status.ret != KSMBD_TREE_CONN_STATUS_OK) smb2_set_err_rsp(work); + if (tree_conn) + ksmbd_tree_connect_put(tree_conn); + return rc; } @@ -3048,17 +3057,6 @@ int smb2_tree_disconnect(struct ksmbd_work *work) ksmbd_close_tree_conn_fds(work); - down_write(&sess->tree_conns_lock); - if (tcon->t_state == TREE_DISCONNECTED) { - up_write(&sess->tree_conns_lock); - rsp->hdr.Status = STATUS_NETWORK_NAME_DELETED; - err = -ENOENT; - goto err_out; - } - - tcon->t_state = TREE_DISCONNECTED; - up_write(&sess->tree_conns_lock); - err = ksmbd_tree_conn_disconnect(sess, tcon); if (err) { rsp->hdr.Status = STATUS_NETWORK_NAME_DELETED; base-commit: f7e5381fe0e2956317075a6d24aad1f56d6ce382 -- 2.55.0