Re: [dpdk-dev] [PATCH v2] mbuf: fix out-of-bounds access

[Olivier Matz <olivier.matz@6wind.com>]

On Thu, Jun 11, 2020 at 08:48:01AM +0800, Xiaolong Ye wrote:
> We should make sure off + size < sizeof(struct rte_mbuf) to avoid
> possible out-of-bounds access of free_space array, there is no issue
> currently due to the low bits of free_flags (which is adjacent to
> free_space) are always set to 0. But we shouldn't rely on it since it's
> fragile and layout of struct mbuf_dyn_shm may be changed in the future.
> This patch adds boundary check explicitly to avoid potential risk of
> out-of-bounds access.
> 
> Fixes: 4958ca3a443a ("mbuf: support dynamic fields and flags")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Xiaolong Ye <xiaolong.ye@intel.com>

I suggest to change the title in:
mbuf: fix out-of-bounds access at dyn field register

Thomas, as Xiaolong pointed-out, it fixes a bug in the code but there is
no impact. I let you decide if it should be tagged as a fix or not, and
if it should be backported. I'll tend to say yes.

Acked-by: Olivier Matz <olivier.matz@6wind.com>

> ---
> 
> V2: put the check before accessing free_space
> 
>  lib/librte_mbuf/rte_mbuf_dyn.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_mbuf/rte_mbuf_dyn.c b/lib/librte_mbuf/rte_mbuf_dyn.c
> index d6931f847..9d6388cff 100644
> --- a/lib/librte_mbuf/rte_mbuf_dyn.c
> +++ b/lib/librte_mbuf/rte_mbuf_dyn.c
> @@ -71,7 +71,8 @@ process_score(void)
>  
>  	for (off = 0; off < sizeof(struct rte_mbuf); off++) {
>  		/* get the size of the free zone */
> -		for (size = 0; shm->free_space[off + size]; size++)
> +		for (size = 0; (off + size) < sizeof(struct rte_mbuf) &&
> +			     shm->free_space[off + size]; size++)
>  			;
>  		if (size == 0)
>  			continue;
> -- 
> 2.17.1
>