ext4: avoid unneeded lookup when xattr name is invalid

In ext4_xattr_set_handle() we have checked the xattr name's length. So we should also check it in ext4_xattr_get() to avoid unneeded lookup caused by invalid name.

In addition, we deleted the check of NULL in ext4_xattr_set_handle(), because in all the callers of the ext4_xattr_set_handle(), the name can't be NULL.

---
 fs/ext4/xattr.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

index 1f5cf58..340bdfa 100644
@@ -369,6 +369,9 @@ ext4_xattr_get(struct inode *inode, int name_index, const char *name,
 {
 	int error;
 
+	if (strlen(name) > 255)
+		return -ERANGE;
+
 	down_read(&EXT4_I(inode)->xattr_sem);
 	error = ext4_xattr_ibody_get(inode, name_index, name, buffer,
 				     buffer_size);

@@ -1073,8 +1076,6 @@ ext4_xattr_set_handle(handle_t *handle, struct inode *inode, int name_index,
 	unsigned long no_expand;
 	int error;
 
-	if (!name)
-		return -EINVAL;
 	if (strlen(name) > 255)
 		return -ERANGE;
 	down_write(&EXT4_I(inode)->xattr_sem);

1.8.5.5


.

Applied, although I dropped this bit:

Verifying this is non-trivial, since there are many non-local users of this function, and in order to make sure this is true you need to verify (at least) the callers of the callers. I could be convinced to turn this into a BUG_ON(!name), or "if (unlikely(!name))", but leaving the check in is a good idea, since even if it is true today, it's not necessarily guarantted to be true N years in the future.

- Ted