Extend anon_inode_make_secure_inode() to take superblock parameter and
make it available via fs.h. This allows other subsystems to create
anonymous inodes with proper security context.
Use this function in secretmem to fix a security regression, where
S_PRIVATE flag wasn't cleared after alloc_anon_inode(), causing
LSM/SELinux checks to be skipped.
Using anon_inode_make_secure_inode() ensures proper security context
initialization through security_inode_init_security_anon().
Fixes: 2bfe15c52612 ("mm: create security context for memfd_secret inodes")
Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
Suggested-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
Signed-off-by: Shivank Garg <shivankg@xxxxxxx>
---
The handling of the S_PRIVATE flag for these inodes was discussed
extensively ([1], [2], [3]).
As per discussion [3] with Mike and Paul, KVM guest_memfd and secretmem
result in user-visible file descriptors, so they should be subject to
LSM/SELinux security policies rather than bypassing them with S_PRIVATE.
[1] https://lore.kernel.org/all/b9e5fa41-62fd-4b3d-bb2d-24ae9d3c33da@xxxxxxxxxx
[2] https://lore.kernel.org/all/cover.1748890962.git.ackerleytng@xxxxxxxxxx
[3] https://lore.kernel.org/all/aFOh8N_rRdSi_Fbc@xxxxxxxxxx
V3:
- Drop EXPORT to be added later in separate patch for KVM guest_memfd and
keep this patch focused on fix.
V2: https://lore.kernel.org/all/20250620070328.803704-3-shivankg@xxxxxxx
- Use EXPORT_SYMBOL_GPL_FOR_MODULES() since KVM is the only user.
V1: https://lore.kernel.org/all/20250619073136.506022-2-shivankg@xxxxxxx
fs/anon_inodes.c | 22 +++++++++++++++++-----
include/linux/fs.h | 2 ++
mm/secretmem.c | 9 +--------
3 files changed, 20 insertions(+), 13 deletions(-)
diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index e51e7d88980a..c530405edd15 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -98,14 +98,25 @@ static struct file_system_type anon_inode_fs_type = {
.kill_sb = kill_anon_super,
};
-static struct inode *anon_inode_make_secure_inode(
- const char *name,
- const struct inode *context_inode)
+/**
+ * anon_inode_make_secure_inode - allocate an anonymous inode with security context
+ * @sb: [in] Superblock to allocate from
+ * @name: [in] Name of the class of the new file (e.g., "secretmem")
+ * @context_inode:
+ * [in] Optional parent inode for security inheritance
+ *
+ * The function ensures proper security initialization through the LSM hook
+ * security_inode_init_security_anon().
+ *
+ * Return: Pointer to new inode on success, ERR_PTR on failure.
+ */
+struct inode *anon_inode_make_secure_inode(struct super_block *sb, const char *name,
+ const struct inode *context_inode)
{
struct inode *inode;
int error;
- inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
+ inode = alloc_anon_inode(sb);
if (IS_ERR(inode))
return inode;
inode->i_flags &= ~S_PRIVATE;
@@ -132,7 +143,8 @@ static struct file *__anon_inode_getfile(const char *name,
return ERR_PTR(-ENOENT);
if (make_inode) {
- inode = anon_inode_make_secure_inode(name, context_inode);
+ inode = anon_inode_make_secure_inode(anon_inode_mnt->mnt_sb,
+ name, context_inode);
if (IS_ERR(inode)) {
file = ERR_CAST(inode);
goto err;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b085f161ed22..040c0036320f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3608,6 +3608,8 @@ extern int simple_write_begin(struct file *file, struct address_space *mapping,
extern const struct address_space_operations ram_aops;
extern int always_delete_dentry(const struct dentry *);
extern struct inode *alloc_anon_inode(struct super_block *);
+struct inode *anon_inode_make_secure_inode(struct super_block *sb, const char *name,
+ const struct inode *context_inode);
extern int simple_nosetlease(struct file *, int, struct file_lease **, void **);
extern const struct dentry_operations simple_dentry_operations;
diff --git a/mm/secretmem.c b/mm/secretmem.c
index 589b26c2d553..9a11a38a6770 100644
--- a/mm/secretmem.c
+++ b/mm/secretmem.c
@@ -195,18 +195,11 @@ static struct file *secretmem_file_create(unsigned long flags)
struct file *file;
struct inode *inode;
const char *anon_name = "[secretmem]";
- int err;
- inode = alloc_anon_inode(secretmem_mnt->mnt_sb);
+ inode = anon_inode_make_secure_inode(secretmem_mnt->mnt_sb, anon_name, NULL);
if (IS_ERR(inode))
return ERR_CAST(inode);
- err = security_inode_init_security_anon(inode, &QSTR(anon_name), NULL);
- if (err) {
- file = ERR_PTR(err);
- goto err_free_inode;
- }
-
file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem",
O_RDWR, &secretmem_fops);
if (IS_ERR(file))
--
2.43.0
