Re: [RFC PATCH v2 3/3] kasan: add interceptors for all string functions

[Andrey Ryabinin <aryabinin@virtuozzo.com>]

On 4/2/19 12:43 PM, Christophe Leroy wrote:
> Hi Dmitry, Andrey and others,
> 
> Do you have any comments to this series ?
> 

I don't see justification for adding all these non-instrumented functions. We need only some subset of these functions
and only on powerpc so far. Arches that don't use str*() that early simply doesn't need not-instrumented __str*() variant.

Also I don't think that auto-replace str* to __str* for all not instrumented files is a good idea, as this will reduce KASAN coverage.
E.g. we don't instrument slub.c but there is no reason to use non-instrumented __str*() functions there.

And finally, this series make bug reporting slightly worse. E.g. let's look at strcpy():

+char *strcpy(char *dest, const char *src)
+{
+	size_t len = __strlen(src) + 1;
+
+	check_memory_region((unsigned long)src, len, false, _RET_IP_);
+	check_memory_region((unsigned long)dest, len, true, _RET_IP_);
+
+	return __strcpy(dest, src);
+}

If src is not-null terminated string we might not see proper out-of-bounds report from KASAN only a crash in __strlen().
Which might make harder to identify where 'src' comes from, where it was allocated and what's the size of allocated area.


> I'd like to know if this approach is ok or if it is better to keep doing as in https://patchwork.ozlabs.org/patch/1055788/
>
I think the patch from link is a better solution to the problem.