On Wed Nov 11, 2020 at 3:22 PM PST, Andrii Nakryiko wrote:
> On Wed, Nov 11, 2020 at 2:46 PM Daniel Xu <dxu@xxxxxxxxx> wrote:
> >
> > 6ae08ae3dea2 ("bpf: Add probe_read_{user, kernel} and probe_read_{user,
> > kernel}_str helpers") introduced a subtle bug where
> > bpf_probe_read_user_str() would potentially copy a few extra bytes after
> > the NUL terminator.
> >
> > This issue is particularly nefarious when strings are used as map keys,
> > as seemingly identical strings can occupy multiple entries in a map.
> >
> > This patchset fixes the issue and introduces a selftest to prevent
> > future regressions.
> >
> > v4 -> v5:
> > * don't read potentially uninitialized memory
>
> I think the bigger problem was that it could overwrite unintended
> memory. E.g., in BPF program, if you had something like:
>
> char my_buf[8 + 3];
> char my_precious_data[5] = {1, 2, 3, 4, 5};
How does that happen?
The
while (max >= sizeof(unsigned long)) {
/* copy 4 bytes */
max -= sizeof(unsigned long)
}
/* copy byte at a time */
where `max` is the user supplied length should prevent that kind of
corruption, right?
[...]
