path: root/lib
diff options
authorMark Rutland <mark.rutland@arm.com>2016-10-11 13:51:27 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-10-11 15:06:30 -0700
commitbf90e56e467ed5766722972d483e6711889ed1b0 (patch)
tree247ecdbbc0e47c0a323e66f523b166c2b5323f24 /lib
parente0176a2f1e131294824d0e50e719cd12290cf06c (diff)
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>
Diffstat (limited to 'lib')
1 files changed, 2 insertions, 0 deletions
diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
index 9c5fe8110413..7e35fc450c5b 100644
--- a/lib/strncpy_from_user.c
+++ b/lib/strncpy_from_user.c
@@ -1,6 +1,7 @@
#include <linux/compiler.h>
#include <linux/export.h>
#include <linux/kasan-checks.h>
+#include <linux/thread_info.h>
#include <linux/uaccess.h>
#include <linux/kernel.h>
#include <linux/errno.h>
@@ -111,6 +112,7 @@ long strncpy_from_user(char *dst, const char __user *src, long count)
long retval;
kasan_check_write(dst, count);
+ check_object_size(dst, count, false);
retval = do_strncpy_from_user(dst, src, count, max);