From bf90e56e467ed5766722972d483e6711889ed1b0 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Tue, 11 Oct 2016 13:51:27 -0700 Subject: [PATCH] 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 Cc: Kees Cook Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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 9c5fe8110413..7e35fc450c5b 100644 --- a/lib/strncpy_from_user.c +++ b/lib/strncpy_from_user.c @@ -1,6 +1,7 @@ #include #include #include +#include #include #include #include @@ -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); user_access_begin(); retval = do_strncpy_from_user(dst, src, count, max); user_access_end();