Hi,
On Tue, Oct 15, 2019 at 05:57:16PM +0200, Pablo Neira Ayuso wrote:
> On Tue, Oct 15, 2019 at 04:16:57PM +0200, Phil Sutter wrote:
> > Array 'tb' has only 'attr_max' elements, the loop overstepped its
> > boundary by one. Copy array_size() macro from include/utils.h in
> > nftables.git to make sure code does the right thing.
> >
> > Fixes: 0adceeab1597a ("src: add ct timeout support")
> > Signed-off-by: Phil Sutter <phil@xxxxxx>
> > ---
> > include/utils.h | 8 ++++++++
> > src/obj/ct_timeout.c | 2 +-
> > 2 files changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/utils.h b/include/utils.h
> > index 3cc659652fe2e..91fbebb1956fd 100644
> > --- a/include/utils.h
> > +++ b/include/utils.h
> > @@ -58,6 +58,14 @@ void __nftnl_assert_attr_exists(uint16_t attr, uint16_t attr_max,
> > ret = remain; \
> > remain -= ret; \
> >
> > +
> > +#define BUILD_BUG_ON_ZERO(e) (sizeof(char[1 - 2 * !!(e)]) - 1)
> > +
> > +#define __must_be_array(a) \
> > + BUILD_BUG_ON_ZERO(__builtin_types_compatible_p(typeof(a), typeof(&a[0])))
> > +
> > +#define array_size(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))
> > +
> > const char *nftnl_family2str(uint32_t family);
> > int nftnl_str2family(const char *family);
> >
> > diff --git a/src/obj/ct_timeout.c b/src/obj/ct_timeout.c
> > index a439432deee18..a09e25ae5d44f 100644
> > --- a/src/obj/ct_timeout.c
> > +++ b/src/obj/ct_timeout.c
> > @@ -134,7 +134,7 @@ timeout_parse_attr_data(struct nftnl_obj *e,
> > if (mnl_attr_parse_nested(nest, parse_timeout_attr_policy_cb, &cnt) < 0)
> > return -1;
> >
> > - for (i = 1; i <= attr_max; i++) {
> > + for (i = 1; i < array_size(tb); i++) {
>
> Are you sure this is correct?
>
> array use NFTNL_CTTIMEOUT_* while tb uses netlink NFTA_* attributes.
The old code can't be correct. Basically it was:
| struct nlattr *tb[attr_max];
[...]
| for (i = 1; i <= attr_max; i++) {
| if (tb[i]) {
[...]
So in the last round, it accesses 'tb[attr_max]' which is out of bounds.
Regarding the question of whether the array is big enough at all, I had
a look at values in 'timeout_protocol' array struct field values
'attr_max': either NFTNL_CTTIMEOUT_TCP_MAX or NFTNL_CTTIMEOUT_UDP_MAX.
Both are last items in unions so serve only for defining array sizes.
Without checking differences between NFTNL_CTTIMEOUT_* and respective
NFTA_* symbols, I'd bet the array is large enough! :)
Cheers, Phil
