f2fs crypto: fix corrupted symlink in encrypted case

In the encrypted symlink case, we should check its corrupted symname after
decrypting it.
Otherwise, we can report -ENOENT incorrectly, if encrypted symname starts with
'\0'.

Cc: stable 4.5+ <stable@vger.kernel.org>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/namei.c

@@ -1027,12 +1027,6 @@ static const char *f2fs_encrypted_get_link(struct dentry *dentry,
 		goto errout;
 	}
 
-	/* this is broken symlink case */
-	if (unlikely(cstr.name[0] == 0)) {
-		res = -ENOENT;
-		goto errout;
-	}
-
 	if ((cstr.len + sizeof(struct fscrypt_symlink_data) - 1) > max_size) {
 		/* Symlink data on the disk is corrupted */
 		res = -EIO;
@@ -1046,6 +1040,12 @@ static const char *f2fs_encrypted_get_link(struct dentry *dentry,
 	if (res < 0)
 		goto errout;
 
+	/* this is broken symlink case */
+	if (unlikely(pstr.name[0] == 0)) {
+		res = -ENOENT;
+		goto errout;
+	}
+
 	paddr = pstr.name;
 
 	/* Null-terminate the name */