From 824e71d68aa91bbc0191748a3c36e8630acbcff9 Mon Sep 17 00:00:00 2001 From: Mark Rutland <mark.rutland@arm.com> Date: Tue, 11 Oct 2016 13:51:27 -0700 Subject: [PATCH] BACKPORT: lib: harden strncpy_from_user The strncpy_from_user() accessor is effectively a copy_from_user() specialised to copy strings, terminating early at a NUL byte if possible. In other respects it is identical, and can be used to copy an arbitrarily large buffer from userspace into the kernel. Conceptually, it exposes a similar attack surface. As with copy_from_user(), we check the destination range when the kernel is built with KASAN, but unlike copy_from_user() we do not check the destination buffer when using HARDENED_USERCOPY. As strncpy_from_user() calls get_user() in a loop, we must call check_object_size() explicitly. This patch adds this instrumentation to strncpy_from_user(), per the same rationale as with the regular copy_from_user(). In the absence of hardened usercopy this will have no impact as the instrumentation expands to an empty static inline function. Link: http://lkml.kernel.org/r/1472221903-31181-1-git-send-email-mark.rutland@arm.com Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Kees Cook <keescook@chromium.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Bug: 31374226 Change-Id: I898e4e9f19307e37a9be497cb1a0d7f1e3911661 (cherry picked from commit bf90e56e467ed5766722972d483e6711889ed1b0) Signed-off-by: Sami Tolvanen <samitolvanen@google.com> --- lib/strncpy_from_user.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c index 5a003a2ebd96..05efc1fa97f0 100644 --- a/lib/strncpy_from_user.c +++ b/lib/strncpy_from_user.c @@ -1,5 +1,6 @@ #include <linux/compiler.h> #include <linux/export.h> +#include <linux/thread_info.h> #include <linux/uaccess.h> #include <linux/kernel.h> #include <linux/errno.h> @@ -109,6 +110,7 @@ long strncpy_from_user(char *dst, const char __user *src, long count) unsigned long max = max_addr - src_addr; long retval; + check_object_size(dst, count, false); user_access_begin(); retval = do_strncpy_from_user(dst, src, count, max); user_access_end(); -- 2.34.1