From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 9604A38B7D1 for ; Thu, 10 Sep 2026 15:27:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789054079; cv=none; b=LXDY3fZrwF2Ja4AWZWv6PJznNbXg7oBnierG55rCrD8xPd7oDQ1EiQgEUEIE838kY6033yobMhaGVlffRFYaM3gkE+KVmRcYz6lQ7waAj2GiSQYeyypjw4Tj3O/cA+kQ5hOxPx8wDNI/EvqWBJ3B0Q6ZKohbNzhpcN5Uy7Gv0AA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789054079; c=relaxed/simple; bh=c6iKL+i/kJhLJB6k9NhqY8jRoqbC4Q+ZSb+sFJV7HXg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=URvA7O4iqvjN5aO+LOxDRzzkGMVJ2bZFVNAls4D9ajVMq9FqmPF92qFPfJEPmSyQAvbgklzNVJT69RTPure8iqNTPMBQ8lMdpS/FqCbCtMkb9ZdVLyoDlnm7h98KaO5ahYMjsjuiy8MjB875UG4KfUxsusxzmGt7B2SwsJeMoPo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BakrnJMg; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="BakrnJMg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8321B1F00893; Thu, 10 Sep 2026 15:27:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789054078; bh=bd3LitVBAL66qknvb+gDhvM3J8u1TfGFW6jzcmj+cOQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=BakrnJMg8r84ZEJyMF1rA+CXPRgAn5naibe0nkmWxKtJcC0KNa67IXfEvGKY0a662 MAWValCoWm62nv2tkWzcxS5Dwt3Ln+kKURSPDJmoeVUkd/nIfUPnMehLM/yUO7/dta AiNB7xNxvzju982NcZ9GMUnUub/vwGdiQvaUL8k9PqudCU+XtK3hNTyDYO2I7ua3jO NhZjuxJIynSMDQAaOHvaBwSdagg42a0t5WL9PjnpR11hUarj4tHTFEogHVSixjkNPY Gq3HFiEZvhNkFkiW1Pxe/kNPluw2rt9oz4+UtAorI1R6OeKPMqciayiqJQCwScUgby J+Z8ievHEsAwA== From: Sasha Levin To: stable@vger.kernel.org Cc: "Cen Zhang (Microsoft Security FORGE Labs)" , "Xiang Mei (Microsoft)" , AutonomousCodeSecurity@microsoft.com, Namjae Jeon , Sasha Levin Subject: [PATCH 7.2.y 3/3] ksmbd: fix tree connection use-after-free in smb2_tree_connect() Date: Thu, 10 Sep 2026 11:27:54 -0400 Message-ID: <20260910152754.950820-3-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260910152754.950820-1-sashal@kernel.org> References: <2026090802-tactical-overplay-91bf@gregkh> <20260910152754.950820-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Cen Zhang (Microsoft Security FORGE Labs)" [ Upstream commit b5ec6c462aab1062cf5d1e667ba7c6442f737055 ] 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) Signed-off-by: Namjae Jeon [ added braces around the successful-connect if branch to accommodate the new tree_conn assignment ] Signed-off-by: Sasha Levin --- fs/smb/server/mgmt/tree_connect.c | 8 ++++++++ fs/smb/server/smb2pdu.c | 32 +++++++++++++++---------------- 2 files changed, 23 insertions(+), 17 deletions(-) diff --git a/fs/smb/server/mgmt/tree_connect.c b/fs/smb/server/mgmt/tree_connect.c index 58e5b8592da46..3d04feaf8737a 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; @@ -127,6 +129,12 @@ 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 64142c1d9020a..cfbfd071f16ea 100644 --- a/fs/smb/server/smb2pdu.c +++ b/fs/smb/server/smb2pdu.c @@ -2251,6 +2251,7 @@ 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; @@ -2277,9 +2278,10 @@ int smb2_tree_connect(struct ksmbd_work *work) name, treename); status = ksmbd_tree_conn_connect(work, name); - if (status.ret == KSMBD_TREE_CONN_STATUS_OK) + 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); - else + } else goto out_err1; share = status.tree_conn->share_conf; @@ -2311,8 +2313,15 @@ 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: if (server_conf.flags & KSMBD_GLOBAL_FLAG_DURABLE_HANDLE && share && @@ -2332,9 +2341,6 @@ 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; } @@ -2375,6 +2381,9 @@ 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; } @@ -2478,17 +2487,6 @@ 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; -- 2.53.0