[dpdk-stable] [PATCH v2] test/hash: fix buffer overflow

[David Marchand]

On Wed, Oct 13, 2021 at 9:28 PM Vladimir Medvedkin
<vladimir.medvedkin at intel.com> wrote:
>
> This patch fixes buffer overflow reported by ASAN,
> please reference https://bugs.dpdk.org/show_bug.cgi?id=818
>
> Some tests for the rte_hash table use the rte_jhash_32b() as
> the hash function. This hash function interprets the length
> argument in units of 4 bytes.
>
> This patch divides configured key length by 4 in cases when
> rte_jhash_32b() is used.
>
> For some tests rte_jhash() is used with keys of length not
> a multiple of 4 bytes. From the rte_jhash() documentation:
> If input key is not aligned to four byte boundaries or a
> multiple of four bytes in length, the memory region just
> after may be read (but not used in the computation).
>
> This patch increases the size of the proto field of the
> flow_key struct up to uint32_t and sets the alignment to 4 bytes.
>
> Bugzilla ID: 818
> Fixes: af75078fece3 ("first public release")
> Cc: stable at dpdk.org
>
> Signed-off-by: Vladimir Medvedkin <vladimir.medvedkin at intel.com>
> ---
>  app/test/test_hash.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/app/test/test_hash.c b/app/test/test_hash.c
> index bd4d0cb..e3f2d29 100644
> --- a/app/test/test_hash.c
> +++ b/app/test/test_hash.c
> @@ -80,8 +80,8 @@ struct flow_key {
>         uint32_t ip_dst;
>         uint16_t port_src;
>         uint16_t port_dst;
> -       uint8_t proto;
> -} __rte_packed;
> +       uint32_t proto;
> +} __rte_packed __rte_aligned(sizeof(uint32_t));

If in the future, we add a field not multiple of sizeof(uint32_t),
there will be some padding at the end of the structure.
I *think* holes and padding content is undefined for initialized
objects (though maybe things could be different with objects in .data
?).
That's probably something to confirm.
If this is the case, the hash function would consider random data.

I think growing the proto field to uint32_t like you did is the right
fix since the whole structure is now naturally uint32_t aligned.

But I would remove the aligned attribute and prefer
RTE_BUILD_BUG(sizeof(struct flow_key) % sizeof(sizeof(uint32_t)) !=
0).
Maybe add a comment to explain we keep the packed attribute to avoid
holes with potentially undefined content in the middle of this struct.


-- 
David Marchand