On 2016-04-14 Kees Cook wrote:
> From: Yinghai Lu <[email protected]>
>
> parse_elf is using a local memcpy to move sections to their final
> running position. However, this memcpy only supports non-overlapping
> arguments (or dest < src).
The same copy of memcpy is used by the decompressors too.
> To avoid future hard-to-debug surprises, this adds checking in memcpy
> to detect the unhandled condition (which should not be happening
> currently).
It's already a minor surprise that memcpy is expected to work for
overlapping buffers at all. It could be good to have a comment about
it because "scroll" and parse_elf seem to rely on it.
On the other hand, the new code and error message take quite a few bytes
of space, so a complete memmove can be smaller:
void *memmove(void *dest, const void *src, size_t n)
{
unsigned char *d = dest;
const unsigned char *s = src;
if (d <= s || d - s >= n)
return __memcpy(dest, src, n);
while (n-- > 0)
d[n] = s[n];
return dest;
}
Note that memmove is needed by lib/decompress_unxz.c. It contains its
own small version inside a "#ifndef memmove" block. That #ifndef should
be taken into account when adding a memmove symbol. Changing
decompress_unxz.c is fine but then one needs to think about other
archs too.
--
Lasse Collin | IRC: Larhzu @ IRCnet & Freenode
