ovl: fix lock in ovl_llseek()

ovl_inode_lock() is interruptible. When inode_lock() in ovl_llseek()
was replaced with ovl_inode_lock(), we did not add a check for error.

Fix this by making ovl_inode_lock() uninterruptible and change the
existing call sites to use an _interruptible variant.

Reported-by: syzbot+66a9752fa927f745385e@syzkaller.appspotmail.com
Fixes: b1f9d38 ("ovl: use ovl_inode_lock in ovl_llseek()")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Author: amir73il

fs/overlayfs/overlayfs.h

@@ -318,7 +318,12 @@ static inline unsigned int ovl_xino_bits(struct super_block *sb)
 	return ovl_same_dev(sb) ? OVL_FS(sb)->xino_mode : 0;
 }
 
-static inline int ovl_inode_lock(struct inode *inode)
+static inline void ovl_inode_lock(struct inode *inode)
+{
+	mutex_lock(&OVL_I(inode)->lock);
+}
+
+static inline int ovl_inode_lock_interruptible(struct inode *inode)
 {
 	return mutex_lock_interruptible(&OVL_I(inode)->lock);
 }

fs/overlayfs/util.c

@@ -509,7 +509,7 @@ int ovl_copy_up_start(struct dentry *dentry, int flags)
 	struct inode *inode = d_inode(dentry);
 	int err;
 
-	err = ovl_inode_lock(inode);
+	err = ovl_inode_lock_interruptible(inode);
 	if (!err && ovl_already_copied_up_locked(dentry, flags)) {
 		err = 1; /* Already copied up */
 		ovl_inode_unlock(inode);
@@ -764,7 +764,7 @@ int ovl_nlink_start(struct dentry *dentry)
 			return err;
 	}
 
-	err = ovl_inode_lock(inode);
+	err = ovl_inode_lock_interruptible(inode);
 	if (err)
 		return err;