FAILED: patch "[PATCH] landlock: Fix use-after-free of the source's parent directory" failed to apply to 6.12-stable tree

PATCH New [email protected] 2 participants 3 messages Sep 16 – Sep 17

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Stable branch Security (LSM) Landlock security module

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author maintainer

2026-09-16 16:07 UTC #0 lore raw

The patch below does not apply to the 6.12-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-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x 2c6dc792538260a8087ac5b22c31b3b8e47c85d6
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026091642-android-strode-2706@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 2c6dc792538260a8087ac5b22c31b3b8e47c85d6 Mon Sep 17 00:00:00 2001
From: Norbert Szetei <[email protected]>
Date: Sat, 22 Aug 2026 14:29:00 +0200
Subject: [PATCH] landlock: Fix use-after-free of the source's parent directory
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

current_check_refer_path() reads old_dentry->d_parent without holding a reference nor a lock on it, and then dereferences it in collect_domain_accesses() and in the audit record.

A reference on a child does not pin its parent: __d_move() reassigns dentry->d_parent and drops the reference the child held on its former parent. hook_path_rename() is not affected because the rename path calls lock_rename() before the hook, so the source cannot be reparented under it. hook_path_link() has no such protection: filename_linkat() holds a reference on the source dentry but neither locks nor references its parent, so a concurrent rename(2) can reparent the source while security_path_link() runs, and the former parent can then be removed and freed while the hook walks it.

A process can trigger this after entering a Landlock domain that handles at least one filesystem access right. The process can then race a linkat(2) loop against rename(2) and rmdir(2):

  BUG: KASAN: slab-use-after-free in collect_domain_accesses+0x278/0x290
  Read of size 4 at addr ffff888160bd53f4 by task llrepro2/549
   collect_domain_accesses+0x278/0x290
   current_check_refer_path+0x952/0x1120
   security_path_link+0x1be/0x320
   filename_linkat+0x342/0x6d0
   __x64_sys_linkat+0xfa/0x150
  Freed by task 562:
   kmem_cache_free+0x139/0x4c0
   i_callback+0x4b/0x80
   rcu_core+0x7dc/0x10a0

Take a reference on the dentry selected as the source parent, using dget() for the common-mount-root case and dget_parent() otherwise. Release it after the hierarchy walk and synchronous audit logging.

Cc [email protected]

Fixes b91c3e4ea756 ("landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER")

Signed-off-by Norbert Szetei <[email protected]>

Reviewed-by Günther Noack <[email protected]>

Tested-by Günther Noack <[email protected]>

Link https://patch.msgid.link/[email protected] open here

[mic: Clarify the caller, reachability, and reference handling]

Signed-off-by Mickaël Salaün <[email protected]>

security/landlock/fs.c +12 -6

index 30aa6ce13590..330a1871bf94 100644
@@ -1298,11 +1298,12 @@ static int current_check_refer_path(struct dentry *const old_dentry,
 	/*
 	 * old_dentry may be the root of the common mount point and
 	 * !IS_ROOT(old_dentry) at the same time (e.g. with open_tree() and
-	 * OPEN_TREE_CLONE).  We do not need to call dget(old_parent) because
-	 * we keep a reference to old_dentry.
+	 * OPEN_TREE_CLONE).  Pin the dentry used as old_parent in either case.
+	 * Otherwise, dget_parent() safely fetches and pins the current parent
+	 * against a concurrent rename(2).
 	 */
-	old_parent = (old_dentry == mnt_dir.dentry) ? old_dentry :
-						      old_dentry->d_parent;
+	old_parent = (old_dentry == mnt_dir.dentry) ? dget(old_dentry) :
+						      dget_parent(old_dentry);
 
 	/* new_dir->dentry is equal to new_dentry->d_parent */
 	allow_parent1 = collect_domain_accesses(subject->domain, mnt_dir.dentry,

@@ -1311,8 +1312,10 @@ static int current_check_refer_path(struct dentry *const old_dentry,
 	allow_parent2 = collect_domain_accesses(subject->domain, mnt_dir.dentry,
 						new_dir->dentry,
 						&layer_masks_parent2);
-	if (allow_parent1 && allow_parent2)
+	if (allow_parent1 && allow_parent2) {
+		dput(old_parent);
 		return 0;
+	}
 
 	/*
 	 * To be able to compare source and destination domain access rights,

@@ -1324,8 +1327,10 @@ static int current_check_refer_path(struct dentry *const old_dentry,
 		    subject->domain, &mnt_dir, access_request_parent1,
 		    &layer_masks_parent1, &request1, old_dentry,
 		    access_request_parent2, &layer_masks_parent2, &request2,
-		    exchange ? new_dentry : NULL))
+		    exchange ? new_dentry : NULL)) {
+		dput(old_parent);
 		return 0;
+	}
 
 	if (request1.access) {
 		request1.audit.u.path.dentry = old_parent;

@@ -1335,6 +1340,7 @@ static int current_check_refer_path(struct dentry *const old_dentry,
 		request2.audit.u.path.dentry = new_dir->dentry;
 		landlock_log_denial(subject, &request2);
 	}
+	dput(old_parent);
 
 	/*
 	 * This prioritizes EACCES over EXDEV for all actions, including

Sasha Levin

maintainer

2026-09-17 02:27 UTC #1 lore raw

PATCH 1/2 landlock: Clarify documentation for the IOCTL access right

From: Günther Noack <[email protected]>

[ Upstream commit 6abbb8703aeeb645a681ab6ad155e0b450413787 ]

Move the description of the LANDLOCK_ACCESS_FS_IOCTL_DEV access right together with the file access rights.

This group of access rights applies to files (in this case device files), and they can be added to file or directory inodes using landlock_add_rule(2). The check for that works the same for all file access rights, including LANDLOCK_ACCESS_FS_IOCTL_DEV.

Invoking ioctl(2) on directory FDs can not currently be restricted with Landlock. Having it grouped separately in the documentation is a remnant from earlier revisions of the LANDLOCK_ACCESS_FS_IOCTL_DEV patch set.

Link https://lore.kernel.org/all/[email protected]/ open here

Signed-off-by Günther Noack <[email protected]>

Link https://lore.kernel.org/r/[email protected] open here

Signed-off-by Mickaël Salaün <[email protected]>

Stable-dep-of: 2c6dc7925382 ("landlock: Fix use-after-free of the source's parent directory")

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

---
 include/uapi/linux/landlock.h | 37 ++++++++++++++++-------------------
 1 file changed, 17 insertions(+), 20 deletions(-)

include/uapi/linux/landlock.h +17 ~~-20~~

index 94cfad88082f3..7d9158a3e7928 100644
@@ -156,6 +156,23 @@ struct landlock_net_port_attr {
  *   :manpage:`ftruncate(2)`, :manpage:`creat(2)`, or :manpage:`open(2)` with
  *   ``O_TRUNC``.  This access right is available since the third version of the
  *   Landlock ABI.
+ * - %LANDLOCK_ACCESS_FS_IOCTL_DEV: Invoke :manpage:`ioctl(2)` commands on an opened
+ *   character or block device.
+ *
+ *   This access right applies to all `ioctl(2)` commands implemented by device
+ *   drivers.  However, the following common IOCTL commands continue to be
+ *   invokable independent of the %LANDLOCK_ACCESS_FS_IOCTL_DEV right:
+ *
+ *   * IOCTL commands targeting file descriptors (``FIOCLEX``, ``FIONCLEX``),
+ *   * IOCTL commands targeting file descriptions (``FIONBIO``, ``FIOASYNC``),
+ *   * IOCTL commands targeting file systems (``FIFREEZE``, ``FITHAW``,
+ *     ``FIGETBSZ``, ``FS_IOC_GETFSUUID``, ``FS_IOC_GETFSSYSFSPATH``)
+ *   * Some IOCTL commands which do not make sense when used with devices, but
+ *     whose implementations are safe and return the right error codes
+ *     (``FS_IOC_FIEMAP``, ``FICLONE``, ``FICLONERANGE``, ``FIDEDUPERANGE``)
+ *
+ *   This access right is available since the fifth version of the Landlock
+ *   ABI.
  *
  * Whether an opened file can be truncated with :manpage:`ftruncate(2)` or used
  * with `ioctl(2)` is determined during :manpage:`open(2)`, in the same way as

@@ -216,26 +233,6 @@ struct landlock_net_port_attr {
  *   If multiple requirements are not met, the ``EACCES`` error code takes
  *   precedence over ``EXDEV``.
  *
- * The following access right applies both to files and directories:
- *
- * - %LANDLOCK_ACCESS_FS_IOCTL_DEV: Invoke :manpage:`ioctl(2)` commands on an opened
- *   character or block device.
- *
- *   This access right applies to all `ioctl(2)` commands implemented by device
- *   drivers.  However, the following common IOCTL commands continue to be
- *   invokable independent of the %LANDLOCK_ACCESS_FS_IOCTL_DEV right:
- *
- *   * IOCTL commands targeting file descriptors (``FIOCLEX``, ``FIONCLEX``),
- *   * IOCTL commands targeting file descriptions (``FIONBIO``, ``FIOASYNC``),
- *   * IOCTL commands targeting file systems (``FIFREEZE``, ``FITHAW``,
- *     ``FIGETBSZ``, ``FS_IOC_GETFSUUID``, ``FS_IOC_GETFSSYSFSPATH``)
- *   * Some IOCTL commands which do not make sense when used with devices, but
- *     whose implementations are safe and return the right error codes
- *     (``FS_IOC_FIEMAP``, ``FICLONE``, ``FICLONERANGE``, ``FIDEDUPERANGE``)
- *
- *   This access right is available since the fifth version of the Landlock
- *   ABI.
- *
  * .. warning::
  *
  *   It is currently not possible to restrict some file-related actions

Signature · 1 line

2.53.0

Sasha Levin

maintainer

2026-09-17 02:27 UTC #2 lore raw

PATCH 2/2 landlock: Fix use-after-free of the source's parent directory

From: Norbert Szetei <[email protected]>

[ Upstream commit 2c6dc792538260a8087ac5b22c31b3b8e47c85d6 ]

current_check_refer_path() reads old_dentry->d_parent without holding a reference nor a lock on it, and then dereferences it in collect_domain_accesses() and in the audit record.

A process can trigger this after entering a Landlock domain that handles at least one filesystem access right. The process can then race a linkat(2) loop against rename(2) and rmdir(2):

  BUG: KASAN: slab-use-after-free in collect_domain_accesses+0x278/0x290
  Read of size 4 at addr ffff888160bd53f4 by task llrepro2/549
   collect_domain_accesses+0x278/0x290
   current_check_refer_path+0x952/0x1120
   security_path_link+0x1be/0x320
   filename_linkat+0x342/0x6d0
   __x64_sys_linkat+0xfa/0x150
  Freed by task 562:
   kmem_cache_free+0x139/0x4c0
   i_callback+0x4b/0x80
   rcu_core+0x7dc/0x10a0

Cc [email protected]

Fixes b91c3e4ea756 ("landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER")

Signed-off-by Norbert Szetei <[email protected]>

Reviewed-by Günther Noack <[email protected]>

Tested-by Günther Noack <[email protected]>

Link https://patch.msgid.link/[email protected] open here

[mic: Clarify the caller, reachability, and reference handling]

Signed-off-by Mickaël Salaün <[email protected]>

[ adapted to older Landlock helpers using dom and lacking audit arguments. ]

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

---
 security/landlock/fs.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

security/landlock/fs.c +12 -6

index b96a4daa5b2a2..5b852c2965cf2 100644
@@ -1192,11 +1192,12 @@ static int current_check_refer_path(struct dentry *const old_dentry,
 	/*
 	 * old_dentry may be the root of the common mount point and
 	 * !IS_ROOT(old_dentry) at the same time (e.g. with open_tree() and
-	 * OPEN_TREE_CLONE).  We do not need to call dget(old_parent) because
-	 * we keep a reference to old_dentry.
+	 * OPEN_TREE_CLONE).  Pin the dentry used as old_parent in either case.
+	 * Otherwise, dget_parent() safely fetches and pins the current parent
+	 * against a concurrent rename(2).
 	 */
-	old_parent = (old_dentry == mnt_dir.dentry) ? old_dentry :
-						      old_dentry->d_parent;
+	old_parent = (old_dentry == mnt_dir.dentry) ? dget(old_dentry) :
+						      dget_parent(old_dentry);
 
 	/* new_dir->dentry is equal to new_dentry->d_parent */
 	allow_parent1 = collect_domain_accesses(dom, mnt_dir.dentry, old_parent,

@@ -1204,8 +1205,10 @@ static int current_check_refer_path(struct dentry *const old_dentry,
 	allow_parent2 = collect_domain_accesses(
 		dom, mnt_dir.dentry, new_dir->dentry, &layer_masks_parent2);
 
-	if (allow_parent1 && allow_parent2)
+	if (allow_parent1 && allow_parent2) {
+		dput(old_parent);
 		return 0;
+	}
 
 	/*
 	 * To be able to compare source and destination domain access rights,

@@ -1216,8 +1219,11 @@ static int current_check_refer_path(struct dentry *const old_dentry,
 	if (is_access_to_paths_allowed(
 		    dom, &mnt_dir, access_request_parent1, &layer_masks_parent1,
 		    old_dentry, access_request_parent2, &layer_masks_parent2,
-		    exchange ? new_dentry : NULL))
+		    exchange ? new_dentry : NULL)) {
+		dput(old_parent);
 		return 0;
+	}
+	dput(old_parent);
 
 	/*
 	 * This prioritizes EACCES over EXDEV for all actions, including

Signature · 1 line

2.53.0