[PATCH v2 14/16] overlayfs/xattrs: 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_xattr_set() 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/xattrs.c | 31 +++++++++++++------------------
 1 file changed, 13 insertions(+), 18 deletions(-)

diff --git a/fs/overlayfs/xattrs.c b/fs/overlayfs/xattrs.c
index 0d315d0dd89e..c7eb3d06a9b8 100644
--- a/fs/overlayfs/xattrs.c
+++ b/fs/overlayfs/xattrs.c
@@ -41,15 +41,14 @@ static int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char
 	struct dentry *upperdentry = ovl_i_dentry_upper(inode);
 	struct dentry *realdentry = upperdentry ?: ovl_dentry_lower(dentry);
 	struct path realpath;
-	const struct cred *old_cred;
 
 	if (!value && !upperdentry) {
 		ovl_path_lower(dentry, &realpath);
-		old_cred = ovl_override_creds_light(dentry->d_sb);
-		err = vfs_getxattr(mnt_idmap(realpath.mnt), realdentry, name, NULL, 0);
-		revert_creds_light(old_cred);
+		cred_scoped_guard(ovl_creds(dentry->d_sb))
+			err = vfs_getxattr(mnt_idmap(realpath.mnt), realdentry, name, NULL, 0);
 		if (err < 0)
 			goto out;
+
 	}
 
 	if (!upperdentry) {
@@ -64,15 +63,15 @@ static int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char
 	if (err)
 		goto out;
 
-	old_cred = ovl_override_creds_light(dentry->d_sb);
-	if (value) {
-		err = ovl_do_setxattr(ofs, realdentry, name, value, size,
-				      flags);
-	} else {
-		WARN_ON(flags != XATTR_REPLACE);
-		err = ovl_do_removexattr(ofs, realdentry, name);
+	cred_scoped_guard(ovl_creds(dentry->d_sb)) {
+		if (value) {
+			err = ovl_do_setxattr(ofs, realdentry, name, value, size,
+					      flags);
+		} else {
+			WARN_ON(flags != XATTR_REPLACE);
+			err = ovl_do_removexattr(ofs, realdentry, name);
+		}
 	}
-	revert_creds_light(old_cred);
 	ovl_drop_write(dentry);
 
 	/* copy c/mtime */
@@ -85,13 +84,11 @@ static int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char
 			 void *value, size_t size)
 {
 	ssize_t res;
-	const struct cred *old_cred;
 	struct path realpath;
 
 	ovl_i_path_real(inode, &realpath);
-	old_cred = ovl_override_creds_light(dentry->d_sb);
+	cred_guard(ovl_creds(dentry->d_sb));
 	res = vfs_getxattr(mnt_idmap(realpath.mnt), realpath.dentry, name, value, size);
-	revert_creds_light(old_cred);
 	return res;
 }
 
@@ -116,12 +113,10 @@ ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 	ssize_t res;
 	size_t len;
 	char *s;
-	const struct cred *old_cred;
 	size_t prefix_len, name_len;
 
-	old_cred = ovl_override_creds_light(dentry->d_sb);
+	cred_guard(ovl_creds(dentry->d_sb));
 	res = vfs_listxattr(realdentry, list, size);
-	revert_creds_light(old_cred);
 	if (res <= 0 || size == 0)
 		return res;
 
-- 
2.46.0