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fs: export anon_inode_make_secure_inode() and fix secretmem LSM bypass

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Export anon_inode_make_secure_inode() to allow KVM guest_memfd to create
anonymous inodes with proper security context. This replaces the current
pattern of calling alloc_anon_inode() followed by
inode_init_security_anon() for creating security context manually.

This change also fixes a security regression in secretmem where the
S_PRIVATE flag was not cleared after alloc_anon_inode(), causing
LSM/SELinux checks to be bypassed for secretmem file descriptors.

As guest_memfd currently resides in the KVM module, we need to export this
symbol for use outside the core kernel. In the future, guest_memfd might be
moved to core-mm, at which point the symbols no longer would have to be
exported. When/if that happens is still unclear.

Fixes: 2bfe15c526 ("mm: create security context for memfd_secret inodes")
Suggested-by: David Hildenbrand <david@redhat.com>
Suggested-by: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Shivank Garg <shivankg@amd.com>
Link: https://lore.kernel.org/20250620070328.803704-3-shivankg@amd.com
Acked-by: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Shivank Garg 2025-06-20 07:03:30 +00:00 committed by Christian Brauner
parent 6a68d28066
commit cbe4134ea4
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
3 changed files with 21 additions and 13 deletions
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23
fs/anon_inodes.c
View File

@ -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 newfile (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;
@ -118,6 +129,7 @@ static struct inode *anon_inode_make_secure_inode(
}
return inode;
}
EXPORT_SYMBOL_GPL_FOR_MODULES(anon_inode_make_secure_inode, "kvm");
static struct file *__anon_inode_getfile(const char *name,
const struct file_operations *fops,
@ -132,7 +144,8 @@ 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;

2
include/linux/fs.h
View File

@ -3606,6 +3606,8 @@ 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;

9
mm/secretmem.c
View File

@ -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))