linux-kernel - Re: [PATCH] net: atlantic: Avoid out-of-bounds indexing

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Message-ID: <20220304212447.074c8caf@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 4 Mar 2022 21:24:47 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     irusskikh@...vell.com, davem@...emloft.net,
        Mario Limonciello <mario.limonciello@....com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: atlantic: Avoid out-of-bounds indexing

On Fri,  4 Mar 2022 13:08:12 +0800 Kai-Heng Feng wrote:
> UBSAN warnings are observed on atlantic driver:
> [ 294.432996] UBSAN: array-index-out-of-bounds in /build/linux-Qow4fL/linux-5.15.0/drivers/net/ethernet/aquantia/atlantic/aq_nic.c:484:48
> [ 294.433695] index 8 is out of range for type 'aq_vec_s *[8]'
> 
> The index is assigned right before breaking out the loop, so there's no actual
> deferencing happening.

I think you're underselling it. This codes does not compute the address
of the ring, it reads the ring pointer from an array. The description
reads like it was doing:

	ring = &self->ring[i];

which would indeed be valid. What the code actually does is not.

Please repost with the commit message improved and a Fixes: tag(s)
pointing to commit(s) where the buggy code was introduced.

> So only use the index inside the loop to fix the issue.
> 
> BugLink: https://bugs.launchpad.net/bugs/1958770
> Tested-by: Mario Limonciello <mario.limonciello@....com>
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
>  .../net/ethernet/aquantia/atlantic/aq_vec.c   | 24 +++++++++----------
>  1 file changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/net/ethernet/aquantia/atlantic/aq_vec.c b/drivers/net/ethernet/aquantia/atlantic/aq_vec.c
> index f4774cf051c97..6ab1f3212d246 100644
> --- a/drivers/net/ethernet/aquantia/atlantic/aq_vec.c
> +++ b/drivers/net/ethernet/aquantia/atlantic/aq_vec.c
> @@ -43,8 +43,8 @@ static int aq_vec_poll(struct napi_struct *napi, int budget)
>  	if (!self) {
>  		err = -EINVAL;
>  	} else {
> -		for (i = 0U, ring = self->ring[0];
> -			self->tx_rings > i; ++i, ring = self->ring[i]) {
> +		for (i = 0U; self->tx_rings > i; ++i) {
> +			ring = self->ring[i];
>  			u64_stats_update_begin(&ring[AQ_VEC_RX_ID].stats.rx.syncp);
>  			ring[AQ_VEC_RX_ID].stats.rx.polls++;
>  			u64_stats_update_end(&ring[AQ_VEC_RX_ID].stats.rx.syncp);