[PATCH v2 12/16] overlayfs/namei: Convert to cred_guard()

[Vinicius Costa Gomes <vinicius.gomes@xxxxxxxxx>]

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

Only ovl_maybe_lookup_lowerdata() 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@xxxxxxxxx>
---
 fs/overlayfs/namei.c | 20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index e52d6ae8eeb5..723731bc3678 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -953,15 +953,12 @@ static int ovl_maybe_validate_verity(struct dentry *dentry)
 		return err;
 
 	if (!ovl_test_flag(OVL_VERIFIED_DIGEST, inode)) {
-		const struct cred *old_cred;
-
-		old_cred = ovl_override_creds_light(dentry->d_sb);
+		cred_guard(ovl_creds(dentry->d_sb));
 
 		err = ovl_validate_verity(ofs, &metapath, &datapath);
 		if (err == 0)
 			ovl_set_flag(OVL_VERIFIED_DIGEST, inode);
 
-		revert_creds_light(old_cred);
 	}
 
 	ovl_inode_unlock(inode);
@@ -975,7 +972,6 @@ static int ovl_maybe_lookup_lowerdata(struct dentry *dentry)
 	struct inode *inode = d_inode(dentry);
 	const char *redirect = ovl_lowerdata_redirect(inode);
 	struct ovl_path datapath = {};
-	const struct cred *old_cred;
 	int err;
 
 	if (!redirect || ovl_dentry_lowerdata(dentry))
@@ -993,9 +989,8 @@ static int ovl_maybe_lookup_lowerdata(struct dentry *dentry)
 	if (ovl_dentry_lowerdata(dentry))
 		goto out;
 
-	old_cred = ovl_override_creds_light(dentry->d_sb);
-	err = ovl_lookup_data_layers(dentry, redirect, &datapath);
-	revert_creds_light(old_cred);
+	cred_scoped_guard(ovl_creds(dentry->d_sb))
+		err = ovl_lookup_data_layers(dentry, redirect, &datapath);
 	if (err)
 		goto out_err;
 
@@ -1030,7 +1025,6 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			  unsigned int flags)
 {
 	struct ovl_entry *oe = NULL;
-	const struct cred *old_cred;
 	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
 	struct ovl_entry *poe = OVL_E(dentry->d_parent);
 	struct ovl_entry *roe = OVL_E(dentry->d_sb->s_root);
@@ -1061,7 +1055,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	if (dentry->d_name.len > ofs->namelen)
 		return ERR_PTR(-ENAMETOOLONG);
 
-	old_cred = ovl_override_creds_light(dentry->d_sb);
+	cred_guard(ovl_creds(dentry->d_sb));
 	upperdir = ovl_dentry_upper(dentry->d_parent);
 	if (upperdir) {
 		d.layer = &ofs->layers[0];
@@ -1342,7 +1336,6 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 
 	ovl_dentry_init_reval(dentry, upperdentry, OVL_I_E(inode));
 
-	revert_creds_light(old_cred);
 	if (origin_path) {
 		dput(origin_path->dentry);
 		kfree(origin_path);
@@ -1366,7 +1359,6 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	kfree(upperredirect);
 out:
 	kfree(d.redirect);
-	revert_creds_light(old_cred);
 	return ERR_PTR(err);
 }
 
@@ -1374,7 +1366,6 @@ bool ovl_lower_positive(struct dentry *dentry)
 {
 	struct ovl_entry *poe = OVL_E(dentry->d_parent);
 	const struct qstr *name = &dentry->d_name;
-	const struct cred *old_cred;
 	unsigned int i;
 	bool positive = false;
 	bool done = false;
@@ -1390,7 +1381,7 @@ bool ovl_lower_positive(struct dentry *dentry)
 	if (!ovl_dentry_upper(dentry))
 		return true;
 
-	old_cred = ovl_override_creds_light(dentry->d_sb);
+	cred_guard(ovl_creds(dentry->d_sb));
 	/* Positive upper -> have to look up lower to see whether it exists */
 	for (i = 0; !done && !positive && i < ovl_numlower(poe); i++) {
 		struct dentry *this;
@@ -1423,7 +1414,6 @@ bool ovl_lower_positive(struct dentry *dentry)
 			dput(this);
 		}
 	}
-	revert_creds_light(old_cred);
 
 	return positive;
 }
-- 
2.46.0