On Wed, Jul 24, 2019 at 10:08:57AM -0700, Linus Torvalds wrote: > On Wed, Jul 24, 2019 at 6:09 AM Rasmus Villemoes > <linux@xxxxxxxxxxxxxxxxxx> wrote: > > > > The kernel's snprintf() does not behave in a non-standard way, at least > > not with respect to its return value. > > Note that the kernels snprintf() *does* very much protect against the > overflow case - not by changing the return value, but simply by having > > /* Reject out-of-range values early. Large positive sizes are > used for unknown buffer sizes. */ > if (WARN_ON_ONCE(size > INT_MAX)) > return 0; > > at the very top. > > So you can't actually overflow in the kernel by using the repeated > > offset += vsnprintf( .. size - offset ..); > > model. > > Yes, it's the wrong thing to do, but it is still _safe_. Actually, perhaps we should add this test to strscpy() too? diff --git a/lib/string.c b/lib/string.c index 461fb620f85f..0e0d7628ddc4 100644 --- a/lib/string.c +++ b/lib/string.c @@ -182,7 +182,7 @@ ssize_t strscpy(char *dest, const char *src, size_t count) size_t max = count; long res = 0; - if (count == 0) + if (count == 0 || count > INT_MAX) return -E2BIG; #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS -- Kees Cook
