Unverified Commit cbe4134e authored by Shivank Garg's avatar Shivank Garg Committed by Christian Brauner
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fs: export anon_inode_make_secure_inode() and fix secretmem LSM bypass 



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: 2bfe15c5 ("mm: create security context for memfd_secret inodes")
Suggested-by: default avatarDavid Hildenbrand <david@redhat.com>
Suggested-by: default avatarMike Rapoport <rppt@kernel.org>
Signed-off-by: default avatarShivank Garg <shivankg@amd.com>
Link: https://lore.kernel.org/20250620070328.803704-3-shivankg@amd.com


Acked-by: default avatar"Mike Rapoport (Microsoft)" <rppt@kernel.org>
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 6a68d280

fs/anon_inodes.c

+18 −5
Original line number Diff line number Diff line
@@ -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,

/**

 * 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;

include/linux/fs.h

+2 −0
Original line number Diff line number Diff line
@@ -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;

mm/secretmem.c

+1 −8
Original line number Diff line number Diff line
@@ -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))