FAILED: patch "[PATCH] ksmbd: fix tree connection use-after-free in" failed to apply to 7.2-stable tree

PATCH New [email protected] 2 participants 4 messages Sep 8 – Sep 10

Subsystems (2)

Stable branch Kernel SMB3 server (ksmbd)

lore

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lore

[email protected]

author maintainer

2026-09-08 13:37 UTC #0 lore raw

The patch below does not apply to the 7.2-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-7.2.y
git checkout FETCH_HEAD
git cherry-pick -x b5ec6c462aab1062cf5d1e667ba7c6442f737055
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090802-tactical-overplay-91bf@gregkh' --subject-prefix 'PATCH 7.2.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From b5ec6c462aab1062cf5d1e667ba7c6442f737055 Mon Sep 17 00:00:00 2001
From: "Cen Zhang (Microsoft Security FORGE Labs)"
<[email protected]>
Date: Tue, 1 Sep 2026 14:21:36 -0400
Subject: [PATCH] ksmbd: fix tree connection use-after-free in
smb2_tree_connect()

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) <[email protected]>

Cc [email protected]

Signed-off-by Cen Zhang (Microsoft Security FORGE Labs) <[email protected]>

Signed-off-by Namjae Jeon <[email protected]>

fs/smb/server/mgmt/tree_connect.c +8 -0

index 5f63e236267a..dd1db3554cae 100644
@@ -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);

fs/smb/server/smb2pdu.c +13 ~~-15~~

index d656832d82ef..0ecc52fde69c 100644
@@ -2790,6 +2790,7 @@ 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;

@@ -2817,6 +2818,7 @@ 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;

@@ -2860,8 +2862,15 @@ 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:
 	/*

@@ -2888,9 +2897,6 @@ 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;
 		}

@@ -2931,6 +2937,9 @@ 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;
 }

@@ -3034,17 +3043,6 @@ 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;

Sasha Levin

maintainer

2026-09-10 15:27 UTC #1 lore raw

PATCH 1/3 ksmbd: fix maximum allowed access checks

From: Namjae Jeon <[email protected]>

[ Upstream commit cc2f133e80eb2c4a04bfa77a2f207749fe2f516a ]

The DACL permission check looks for an ACE matching the current user and falls back to the Everyone ACE. It does not consider an Authenticated Users ACE, even though an authenticated session is a member of that well-known group.

As a result, opening a file whose access is granted through S-1-5-11 can incorrectly fail with STATUS_ACCESS_DENIED. Treat an Authenticated Users ACE as a fallback entry alongside Everyone.

The maximal access calculation also combines access masks from every ACE, regardless of whether its SID applies to the current user. This can grant rights belonging to an unrelated principal. Process only ACEs applying to the user, Everyone, or Authenticated Users, and accumulate allowed and denied masks in ACL order. Preserve explicitly requested access bits so they are validated against the resulting maximal mask.

When ACCESS_SYSTEM_SECURITY is denied, report STATUS_PRIVILEGE_NOT_HELD instead of the generic STATUS_ACCESS_DENIED. Access to the system ACL requires a security privilege that ksmbd does not grant.

For regular files, include FILE_EXECUTE in maximal access when the client requested GENERIC_EXECUTE and the DACL grants the complete file-read set. Keep a direct FILE_EXECUTE request subject to the explicit DACL bit. This matches the POSIX file ACL mapping without broadening specific execute requests.

Do not replace rights from an applicable NT ACE with a POSIX ACL entry. The POSIX ACL is only a fallback when no user, Everyone, or Authenticated Users ACE applies; otherwise it can incorrectly broaden the stored DACL.

This fixes smb2.maximum_allowed.maximum_allowed.

Signed-off-by Namjae Jeon <[email protected]>

Stable-dep-of: b5ec6c462aab ("ksmbd: fix tree connection use-after-free in smb2_tree_connect()")

Signed-off-by Sasha Levin <[email protected]>

---
 fs/smb/server/smb2pdu.c |  9 ++++-
 fs/smb/server/smbacl.c  | 83 ++++++++++++++++++++++++++---------------
 fs/smb/server/smbacl.h  |  2 +-
 3 files changed, 61 insertions(+), 33 deletions(-)

fs/smb/server/smb2pdu.c +7 -2

index 76f63f9adc725..9b3ffa0929805 100644
@@ -3601,6 +3601,7 @@ int smb2_open(struct ksmbd_work *work)
 
 	if (file_present && !(req->CreateOptions & FILE_DELETE_ON_CLOSE_LE)) {
 		rc = smb_check_perm_dacl(conn, &path, &daccess,
+					 req->DesiredAccess,
 					 sess->user->uid);
 		if (rc)
 			goto err_out;

@@ -4173,8 +4174,12 @@ int smb2_open(struct ksmbd_work *work)
 			rsp->hdr.Status = STATUS_INVALID_PARAMETER;
 		else if (rc == -EOPNOTSUPP)
 			rsp->hdr.Status = STATUS_NOT_SUPPORTED;
-		else if (rc == -EACCES || rc == -ESTALE || rc == -EXDEV)
-			rsp->hdr.Status = STATUS_ACCESS_DENIED;
+		else if (rc == -EACCES || rc == -ESTALE || rc == -EXDEV) {
+			if (req->DesiredAccess & FILE_ACCESS_SYSTEM_SECURITY_LE)
+				rsp->hdr.Status = STATUS_PRIVILEGE_NOT_HELD;
+			else
+				rsp->hdr.Status = STATUS_ACCESS_DENIED;
+		}
 		else if (rc == -ENOENT)
 			rsp->hdr.Status = STATUS_OBJECT_NAME_INVALID;
 		else if (rc == -EPERM)

fs/smb/server/smbacl.c +53 ~~-30~~

134 lines not on this page · raw message

fs/smb/server/smbacl.h +1 -1

index ab21ba2cd4df3..bf0312bfa0405 100644
@@ -95,7 +95,7 @@ bool smb_inherit_flags(int flags, bool is_dir);
 int smb_inherit_dacl(struct ksmbd_conn *conn, const struct path *path,
 		     unsigned int uid, unsigned int gid);
 int smb_check_perm_dacl(struct ksmbd_conn *conn, const struct path *path,
-			__le32 *pdaccess, int uid);
+			__le32 *pdaccess, __le32 raw_daccess, int uid);
 int set_info_sec(struct ksmbd_conn *conn, struct ksmbd_tree_connect *tcon,
 		 const struct path *path, struct smb_ntsd *pntsd, int ntsd_len,
 		 bool type_check, bool get_write);

Signature · 1 line

2.53.0

Sasha Levin

maintainer

2026-09-10 15:27 UTC #2 lore raw

PATCH 2/3 smb/server: fix tree connection leak in smb2_tree_connect()

From: Ze Tan <[email protected]>

[ Upstream commit 39f2032096715daae5f6fd0f587ca7a474b019df ]

See the procedure below:

smb2_tree_connect
ksmbd_tree_conn_connect
xa_store(&sess->tree_conns, tree_conn->id, tree_conn) ksmbd_counter_inc(KSMBD_COUNTER_TREE_CONNS) ksmbd_share_tree_conn_inc(sc)
ksmbd_iov_pin_rsp // fail
status.ret = KSMBD_TREE_CONN_STATUS_NOMEM
// do not disconnect tree_conn

Disconnect the new tree connection if ksmbd_iov_pin_rsp() fails.

Fixes e2b76ab8b5c9 ("ksmbd: add support for read compound")

Signed-off-by Ze Tan <[email protected]>

Reviewed-by ChenXiaoSong <[email protected]>

Signed-off-by Namjae Jeon <[email protected]>

Stable-dep-of: b5ec6c462aab ("ksmbd: fix tree connection use-after-free in smb2_tree_connect()")

Signed-off-by Sasha Levin <[email protected]>

---
 fs/smb/server/smb2pdu.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

fs/smb/server/smb2pdu.c +9 -1

index 9b3ffa0929805..64142c1d9020a 100644
@@ -2330,8 +2330,16 @@ int smb2_tree_connect(struct ksmbd_work *work)
 		rsp->ShareFlags |= cpu_to_le32(SMB2_SHAREFLAG_COMPRESS_DATA);
 
 	rc = ksmbd_iov_pin_rsp(work, rsp, sizeof(struct smb2_tree_connect_rsp));
-	if (rc)
+	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;
+		}
 		status.ret = KSMBD_TREE_CONN_STATUS_NOMEM;
+	}
 
 	if (!IS_ERR(treename))
 		kfree(treename);

Signature · 1 line

2.53.0

Sasha Levin

maintainer

2026-09-10 15:27 UTC #3 lore raw

PATCH 3/3 ksmbd: fix tree connection use-after-free in smb2_tree_connect()

In reply to Sasha Levin

From: "Cen Zhang (Microsoft Security FORGE Labs)" <[email protected]>

[ Upstream commit b5ec6c462aab1062cf5d1e667ba7c6442f737055 ]

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

Keep the references balanced in every path:

Fixes 33b235a6e6eb ("ksmbd: fix race condition between tree conn lookup and disconnect")

Reported-by Xiang Mei (Microsoft) <[email protected]>

Cc [email protected]

Signed-off-by Cen Zhang (Microsoft Security FORGE Labs) <[email protected]>

Signed-off-by Namjae Jeon <[email protected]>

[ added braces around the successful-connect if branch to accommodate the new tree_conn assignment ]

Signed-off-by Sasha Levin <[email protected]>

---
 fs/smb/server/mgmt/tree_connect.c |  8 ++++++++
 fs/smb/server/smb2pdu.c           | 32 +++++++++++++++----------------
 2 files changed, 23 insertions(+), 17 deletions(-)

fs/smb/server/mgmt/tree_connect.c +8 -0

index 58e5b8592da46..3d04feaf8737a 100644
@@ -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);

fs/smb/server/smb2pdu.c +15 ~~-17~~

index 64142c1d9020a..cfbfd071f16ea 100644
@@ -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;

Signature · 1 line

2.53.0