metag/uaccess: Check access_ok in strncpy_from_user

commit 3a158a62da upstream.

The metag implementation of strncpy_from_user() doesn't validate the src
pointer, which could allow reading of arbitrary kernel memory. Add a
short access_ok() check to prevent that.

Its still possible for it to read across the user/kernel boundary, but
it will invariably reach a NUL character after only 9 bytes, leaking
only a static kernel address being loaded into D0Re0 at the beginning of
__start, which is acceptable for the immediate fix.

Reported-by: Al Viro <>
Signed-off-by: James Hogan <>
Signed-off-by: Greg Kroah-Hartman <>
James Hogan 6 years ago committed by Greg Kroah-Hartman
parent 9fefcb947e
commit e8a8a6972c

@ -194,8 +194,13 @@ do { \
extern long __must_check __strncpy_from_user(char *dst, const char __user *src,
long count);
#define strncpy_from_user(dst, src, count) __strncpy_from_user(dst, src, count)
static inline long
strncpy_from_user(char *dst, const char __user *src, long count)
if (!access_ok(VERIFY_READ, src, 1))
return -EFAULT;
return __strncpy_from_user(dst, src, count);
* Return the size of a string (including the ending 0)