ovl: pass an explicit reference of creators creds to callers

ovl_setup_cred_for_create() decrements one refcount of new creds and
ovl_revert_creds() in callers decrements the last refcount.

In preparation to revert_creds_light() back to caller creds, pass an
explicit reference of the creators creds to the callers and drop the
refcount explicitly in the callers after ovl_revert_creds().

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 09db5eb19242fa40c3bdbf753f25935fff7a9119..4b0bb7a91d37688a1559f8ae31ec2ac659a1ea92 100644 (file)
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -553,15 +553,17 @@ out_cleanup:
        goto out_dput;
 }
 
-static int ovl_setup_cred_for_create(struct dentry *dentry, struct inode *inode,
-                                    umode_t mode, const struct cred *old_cred)
+static const struct cred *ovl_setup_cred_for_create(struct dentry *dentry,
+                                                   struct inode *inode,
+                                                   umode_t mode,
+                                                   const struct cred *old_cred)
 {
        int err;
        struct cred *override_cred;
 
        override_cred = prepare_creds();
        if (!override_cred)
-               return -ENOMEM;
+               return ERR_PTR(-ENOMEM);
 
        override_cred->fsuid = inode->i_uid;
        override_cred->fsgid = inode->i_gid;
@@ -569,19 +571,18 @@ static int ovl_setup_cred_for_create(struct dentry *dentry, struct inode *inode,
                                              old_cred, override_cred);
        if (err) {
                put_cred(override_cred);
-               return err;
+               return ERR_PTR(err);
        }
        put_cred(override_creds(override_cred));
-       put_cred(override_cred);
 
-       return 0;
+       return override_cred;
 }
 
 static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
                              struct ovl_cattr *attr, bool origin)
 {
        int err;
-       const struct cred *old_cred;
+       const struct cred *old_cred, *new_cred = NULL;
        struct dentry *parent = dentry->d_parent;
 
        old_cred = ovl_override_creds(dentry->d_sb);
@@ -610,9 +611,13 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
                 * create a new inode, so just use the ovl mounter's
                 * fs{u,g}id.
                 */
-               err = ovl_setup_cred_for_create(dentry, inode, attr->mode, old_cred);
-               if (err)
+               new_cred = ovl_setup_cred_for_create(dentry, inode, attr->mode,
+                                                    old_cred);
+               err = PTR_ERR(new_cred);
+               if (IS_ERR(new_cred)) {
+                       new_cred = NULL;
                        goto out_revert_creds;
+               }
        }
 
        if (!ovl_dentry_is_whiteout(dentry))
@@ -622,6 +627,7 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
 
 out_revert_creds:
        ovl_revert_creds(old_cred);
+       put_cred(new_cred);
        return err;
 }
 
@@ -1306,7 +1312,7 @@ out:
 static int ovl_create_tmpfile(struct file *file, struct dentry *dentry,
                              struct inode *inode, umode_t mode)
 {
-       const struct cred *old_cred;
+       const struct cred *old_cred, *new_cred = NULL;
        struct path realparentpath;
        struct file *realfile;
        struct dentry *newdentry;
@@ -1315,9 +1321,12 @@ static int ovl_create_tmpfile(struct file *file, struct dentry *dentry,
        int err;
 
        old_cred = ovl_override_creds(dentry->d_sb);
-       err = ovl_setup_cred_for_create(dentry, inode, mode, old_cred);
-       if (err)
+       new_cred = ovl_setup_cred_for_create(dentry, inode, mode, old_cred);
+       err = PTR_ERR(new_cred);
+       if (IS_ERR(new_cred)) {
+               new_cred = NULL;
                goto out_revert_creds;
+       }
 
        ovl_path_upper(dentry->d_parent, &realparentpath);
        realfile = backing_tmpfile_open(&file->f_path, flags, &realparentpath,
@@ -1338,6 +1347,7 @@ static int ovl_create_tmpfile(struct file *file, struct dentry *dentry,
        }
 out_revert_creds:
        ovl_revert_creds(old_cred);
+       put_cred(new_cred);
        return err;
 }