Patch "metag/uaccess: Check access_ok in strncpy_from_user" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

metag/uaccess: Check access_ok in strncpy_from_user

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
metag-uaccess-check-access_ok-in-strncpy_from_user.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: James Hogan <[email protected]>
Date: Tue, 2 May 2017 19:41:06 +0100
Subject: metag/uaccess: Check access_ok in strncpy_from_user

From: James Hogan <[email protected]>

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.

---
 arch/metag/include/asm/uaccess.h |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

@@ -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)
  *

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/metag-uaccess-check-access_ok-in-strncpy_from_user.patch queue-4.4/metag-uaccess-fix-access_ok.patch