4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: James Hogan <james.hogan@xxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxx>
Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx>
Cc: linux-metag@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/metag/include/asm/uaccess.h | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
--- 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)
*