From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: [PATCH 3.16 109/134] metag/uaccess: Check access_ok in strncpy_from_user Date: Fri, 18 Aug 2017 14:13:20 +0100 Message-ID: References: Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-metag-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Cc: akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, James Hogan , Al Viro , linux-metag-u79uwXL29TY76Z2rM5mHXA@public.gmane.org 3.16.47-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: James Hogan 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 Signed-off-by: James Hogan Cc: linux-metag-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Signed-off-by: Ben Hutchings --- 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 @@ -189,8 +189,13 @@ 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) *