net: Make copy_safe_from_sockptr() match documentation

commit eb94b7bb10109a14a5431a67e5d8e31cfa06b395 upstream.

copy_safe_from_sockptr()
  return copy_from_sockptr()
    return copy_from_sockptr_offset()
      return copy_from_user()

copy_from_user() does not return an error on fault. Instead, it returns a
number of bytes that were not copied. Have it handled.

Patch has a side effect: it un-breaks garbage input handling of
nfc_llcp_setsockopt() and mISDN's data_sock_setsockopt().

Fixes: 6309863b31dd ("net: add copy_safe_from_sockptr() helper")
Signed-off-by: Michal Luczaj <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: mmhal

include/linux/sockptr.h

@@ -77,7 +77,9 @@ static inline int copy_safe_from_sockptr(void *dst, size_t ksize,
 {
 	if (optlen < ksize)
 		return -EINVAL;
-	return copy_from_sockptr(dst, optval, ksize);
+	if (copy_from_sockptr(dst, optval, ksize))
+		return -EFAULT;
+	return 0;
 }
 
 static inline int copy_to_sockptr_offset(sockptr_t dst, size_t offset,