[RFC PATCH v2 1/1] fs: Refactor to provide function that allocates a secure anonymous inode

[Ackerley Tng]

alloc_anon_secure_inode() returns an inode after running checks in
security_inode_init_security_anon().

Also refactor secretmem's file creation process to use the new
function.

Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
Change-Id: I4eb8622775bc3d544ec695f453ffd747d9490e40
---
 fs/anon_inodes.c   | 22 ++++++++++++++++------
 include/linux/fs.h |  1 +
 mm/secretmem.c     |  9 +--------
 3 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 583ac81669c2..4c3110378647 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -55,17 +55,20 @@ 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)
+static struct inode *anon_inode_make_secure_inode(struct super_block *s,
+		const char *name, const struct inode *context_inode,
+		bool fs_internal)
 {
 	struct inode *inode;
 	int error;
 
-	inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
+	inode = alloc_anon_inode(s);
 	if (IS_ERR(inode))
 		return inode;
-	inode->i_flags &= ~S_PRIVATE;
+
+	if (!fs_internal)
+		inode->i_flags &= ~S_PRIVATE;
+
 	error =	security_inode_init_security_anon(inode, &QSTR(name),
 						  context_inode);
 	if (error) {
@@ -75,6 +78,12 @@ static struct inode *anon_inode_make_secure_inode(
 	return inode;
 }
 
+struct inode *alloc_anon_secure_inode(struct super_block *s, const char *name)
+{
+	return anon_inode_make_secure_inode(s, name, NULL, true);
+}
+EXPORT_SYMBOL_GPL(alloc_anon_secure_inode);
+
 static struct file *__anon_inode_getfile(const char *name,
 					 const struct file_operations *fops,
 					 void *priv, int flags,
@@ -88,7 +97,8 @@ 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, false);
 		if (IS_ERR(inode)) {
 			file = ERR_CAST(inode);
 			goto err;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 016b0fe1536e..0fded2e3c661 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3550,6 +3550,7 @@ 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 *);
+extern struct inode *alloc_anon_secure_inode(struct super_block *, const char *);
 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 1b0a214ee558..c0e459e58cb6 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 = alloc_anon_secure_inode(secretmem_mnt->mnt_sb, anon_name);
 	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))
-- 
2.49.0.1101.gccaa498523-goog

>> > 
>> > For ease of testing, this series is also available, stitched together,
>> > at https://github.com/googleprodkernel/linux-cc/tree/gmem-1g-page-support-rfc-v2
>> > 
>> 
>> I went digging in your git tree and then found Ryan's set.  So thanks for
>> the git tree.  :-D

Glad that helped!

>> 
>> However, it seems this add another dependency which should be managed in
>> David's email of dependencies?

This is a good idea. David, do you think these two patches should be
managed as a separate patch series in the email of dependencies?

+ (left out of RFCv2, but is above) "fs: Refactor to provide function that allocates a secure anonymous inode"
+ 01/51 "KVM: guest_memfd: Make guest mem use guest mem inodes instead of anonymous inodes"

They're being used by a few patch series now.

>> 
>> Ira
>>