netdev - Re: [PATCH] net: prevent user from passing illegal stab size

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Message-ID: <20210923090054.3556deb0@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Thu, 23 Sep 2021 09:00:54 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     王贇 <yun.wang@...ux.alibaba.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>,
        "open list:TC subsystem" <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: prevent user from passing illegal stab size

On Thu, 23 Sep 2021 17:08:13 +0800 王贇 wrote:
> We observed below report when playing with netlink sock:
> 
>   UBSAN: shift-out-of-bounds in net/sched/sch_api.c:580:10
>   shift exponent 249 is too large for 32-bit type
>   CPU: 0 PID: 685 Comm: a.out Not tainted
>   Call Trace:
>    dump_stack_lvl+0x8d/0xcf
>    ubsan_epilogue+0xa/0x4e
>    __ubsan_handle_shift_out_of_bounds+0x161/0x182
>    __qdisc_calculate_pkt_len+0xf0/0x190
>    __dev_queue_xmit+0x2ed/0x15b0
> 
> it seems like kernel won't check the stab size_log passing from
> user, and will use the insane value later to calculate pkt_len.
> 
> This patch just add a check on the size_log to avoid insane
> calculation.
> 
> Reported-by: Abaci <abaci@...ux.alibaba.com>
> Signed-off-by: Michael Wang <yun.wang@...ux.alibaba.com>
> ---
>  include/uapi/linux/pkt_sched.h | 1 +
>  net/sched/sch_api.c            | 3 +++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
> index ec88590..fa194a0 100644
> --- a/include/uapi/linux/pkt_sched.h
> +++ b/include/uapi/linux/pkt_sched.h
> @@ -98,6 +98,7 @@ struct tc_ratespec {
>  };
> 
>  #define TC_RTAB_SIZE	1024
> +#define TC_LOG_MAX	30

Adding a uAPI define is not necessary.

>  struct tc_sizespec {
>  	unsigned char	cell_log;
> diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
> index 5e90e9b..1b6b8f8 100644
> --- a/net/sched/sch_api.c
> +++ b/net/sched/sch_api.c
> @@ -513,6 +513,9 @@ static struct qdisc_size_table *qdisc_get_stab(struct nlattr *opt,
>  		return stab;
>  	}
> 
> +	if (s->size_log > TC_LOG_MAX)
> +		return ERR_PTR(-EINVAL);

Looks sane, please add an extack message.

Why not cover cell_log as well while at it? 

>  	stab = kmalloc(sizeof(*stab) + tsize * sizeof(u16), GFP_KERNEL);
>  	if (!stab)
>  		return ERR_PTR(-ENOMEM);