The canary in collect_domain_accesses() can be triggered when trying to
link a root mount point. This cannot work in practice because this
directory is mounted, but the VFS check is done after the call to
security_path_link().
Do not use source directory's d_parent when the source directory is the
mount point.
Add tests to check error codes when renaming or linking a mount root
directory. This previously triggered a kernel warning. The
linux/mount.h file is not sorted with other headers to ease backport to
Linux 6.1 .
Cc: Günther Noack <gnoack@xxxxxxxxxx>
Cc: Paul Moore <paul@xxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: syzbot+bf4903dc7e12b18ebc87@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: b91c3e4ea756 ("landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER")
Closes: https://lore.kernel.org/r/000000000000553d3f0618198200@xxxxxxxxxx
Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240516181935.1645983-2-mic@xxxxxxxxxxx
---
security/landlock/fs.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 22d8b7c28074..7877a64cc6b8 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -1110,6 +1110,7 @@ static int current_check_refer_path(struct dentry *const old_dentry,
bool allow_parent1, allow_parent2;
access_mask_t access_request_parent1, access_request_parent2;
struct path mnt_dir;
+ struct dentry *old_parent;
layer_mask_t layer_masks_parent1[LANDLOCK_NUM_ACCESS_FS] = {},
layer_masks_parent2[LANDLOCK_NUM_ACCESS_FS] = {};
@@ -1157,9 +1158,17 @@ static int current_check_refer_path(struct dentry *const old_dentry,
mnt_dir.mnt = new_dir->mnt;
mnt_dir.dentry = new_dir->mnt->mnt_root;
+ /*
+ * 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.
+ */
+ old_parent = (old_dentry == mnt_dir.dentry) ? old_dentry :
+ old_dentry->d_parent;
+
/* new_dir->dentry is equal to new_dentry->d_parent */
- allow_parent1 = collect_domain_accesses(dom, mnt_dir.dentry,
- old_dentry->d_parent,
+ allow_parent1 = collect_domain_accesses(dom, mnt_dir.dentry, old_parent,
&layer_masks_parent1);
allow_parent2 = collect_domain_accesses(
dom, mnt_dir.dentry, new_dir->dentry, &layer_masks_parent2);
--
2.45.0
