[PATCH v2 15/16] overlayfs/util: Convert to cred_guard()

[Vinicius Costa Gomes <vinicius.gomes@intel.com>]

Replace the override_creds_light()/revert_creds_light() pairs of
operations with cred_guard()/cred_scoped_guard().

In ovl_nlink_start() use cred_scoped_guard(), because of
'goto', which can cause the cleanup flow to run on garbage memory.

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
---
 fs/overlayfs/util.c | 24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 80caeb81c727..77b8d01829a4 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -1140,7 +1140,6 @@ static void ovl_cleanup_index(struct dentry *dentry)
 int ovl_nlink_start(struct dentry *dentry)
 {
 	struct inode *inode = d_inode(dentry);
-	const struct cred *old_cred;
 	int err;
 
 	if (WARN_ON(!inode))
@@ -1177,15 +1176,15 @@ int ovl_nlink_start(struct dentry *dentry)
 	if (d_is_dir(dentry) || !ovl_test_flag(OVL_INDEX, inode))
 		return 0;
 
-	old_cred = ovl_override_creds_light(dentry->d_sb);
-	/*
-	 * The overlay inode nlink should be incremented/decremented IFF the
-	 * upper operation succeeds, along with nlink change of upper inode.
-	 * Therefore, before link/unlink/rename, we store the union nlink
-	 * value relative to the upper inode nlink in an upper inode xattr.
-	 */
-	err = ovl_set_nlink_upper(dentry);
-	revert_creds_light(old_cred);
+	cred_scoped_guard(ovl_creds(dentry->d_sb)) {
+		/*
+		 * The overlay inode nlink should be incremented/decremented IFF the
+		 * upper operation succeeds, along with nlink change of upper inode.
+		 * Therefore, before link/unlink/rename, we store the union nlink
+		 * value relative to the upper inode nlink in an upper inode xattr.
+		 */
+		err = ovl_set_nlink_upper(dentry);
+	}
 	if (err)
 		goto out_drop_write;
 
@@ -1206,11 +1205,8 @@ void ovl_nlink_end(struct dentry *dentry)
 	ovl_drop_write(dentry);
 
 	if (ovl_test_flag(OVL_INDEX, inode) && inode->i_nlink == 0) {
-		const struct cred *old_cred;
-
-		old_cred = ovl_override_creds_light(dentry->d_sb);
+		cred_guard(ovl_creds(dentry->d_sb));
 		ovl_cleanup_index(dentry);
-		revert_creds_light(old_cred);
 	}
 
 	ovl_inode_unlock(inode);
-- 
2.46.0