metag/uaccess: Check access_ok in strncpy_from_user

commit 3a158a62da0673db918b53ac1440845a5b64fd90 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 <viro@zeniv.linux.org.uk>
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-metag@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/metag/include/asm/uaccess.h b/arch/metag/include/asm/uaccess.h
index ed6cd90..3db3812 100644 (file)
--- a/arch/metag/include/asm/uaccess.h
+++ b/arch/metag/include/asm/uaccess.h
@@ -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)
  *