netdev - Re: [PATCH] veth: Fix use after free in XDP

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Date:   Wed, 15 Mar 2023 15:19:37 +0900
From:   Toshiaki Makita <toshiaki.makita1@...il.com>
To:     Shawn Bohrer <sbohrer@...udflare.com>
Cc:     toke@...nel.org, makita.toshiaki@....ntt.co.jp,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        kernel-team@...udflare.com, lorenzo@...nel.org
Subject: Re: [PATCH] veth: Fix use after free in XDP_REDIRECT

On 2023/03/15 0:33, Shawn Bohrer wrote:
> 718a18a0c8a67f97781e40bdef7cdd055c430996 "veth: Rework veth_xdp_rcv_skb
> in order to accept non-linear skb" introduced a bug where it tried to
> use pskb_expand_head() if the headroom was less than
> XDP_PACKET_HEADROOM.  This however uses kmalloc to expand the head,
> which will later allow consume_skb() to free the skb while is it still
> in use by AF_XDP.
> 
> Previously if the headroom was less than XDP_PACKET_HEADROOM we
> continued on to allocate a new skb from pages so this restores that
> behavior.
> 
> BUG: KASAN: use-after-free in __xsk_rcv+0x18d/0x2c0
> Read of size 78 at addr ffff888976250154 by task napi/iconduit-g/148640
> 
> CPU: 5 PID: 148640 Comm: napi/iconduit-g Kdump: loaded Tainted: G           O       6.1.4-cloudflare-kasan-2023.1.2 #1
> Hardware name: Quanta Computer Inc. QuantaPlex T41S-2U/S2S-MB, BIOS S2S_3B10.03 06/21/2018
> Call Trace:
>    <TASK>
>    dump_stack_lvl+0x34/0x48
>    print_report+0x170/0x473
>    ? __xsk_rcv+0x18d/0x2c0
>    kasan_report+0xad/0x130
>    ? __xsk_rcv+0x18d/0x2c0
>    kasan_check_range+0x149/0x1a0
>    memcpy+0x20/0x60
>    __xsk_rcv+0x18d/0x2c0
>    __xsk_map_redirect+0x1f3/0x490
>    ? veth_xdp_rcv_skb+0x89c/0x1ba0 [veth]
>    xdp_do_redirect+0x5ca/0xd60
>    veth_xdp_rcv_skb+0x935/0x1ba0 [veth]
>    ? __netif_receive_skb_list_core+0x671/0x920
>    ? veth_xdp+0x670/0x670 [veth]
>    veth_xdp_rcv+0x304/0xa20 [veth]
>    ? do_xdp_generic+0x150/0x150
>    ? veth_xdp_rcv_one+0xde0/0xde0 [veth]
>    ? _raw_spin_lock_bh+0xe0/0xe0
>    ? newidle_balance+0x887/0xe30
>    ? __perf_event_task_sched_in+0xdb/0x800
>    veth_poll+0x139/0x571 [veth]
>    ? veth_xdp_rcv+0xa20/0xa20 [veth]
>    ? _raw_spin_unlock+0x39/0x70
>    ? finish_task_switch.isra.0+0x17e/0x7d0
>    ? __switch_to+0x5cf/0x1070
>    ? __schedule+0x95b/0x2640
>    ? io_schedule_timeout+0x160/0x160
>    __napi_poll+0xa1/0x440
>    napi_threaded_poll+0x3d1/0x460
>    ? __napi_poll+0x440/0x440
>    ? __kthread_parkme+0xc6/0x1f0
>    ? __napi_poll+0x440/0x440
>    kthread+0x2a2/0x340
>    ? kthread_complete_and_exit+0x20/0x20
>    ret_from_fork+0x22/0x30
>    </TASK>
> 
> Freed by task 148640:
>    kasan_save_stack+0x23/0x50
>    kasan_set_track+0x21/0x30
>    kasan_save_free_info+0x2a/0x40
>    ____kasan_slab_free+0x169/0x1d0
>    slab_free_freelist_hook+0xd2/0x190
>    __kmem_cache_free+0x1a1/0x2f0
>    skb_release_data+0x449/0x600
>    consume_skb+0x9f/0x1c0
>    veth_xdp_rcv_skb+0x89c/0x1ba0 [veth]
>    veth_xdp_rcv+0x304/0xa20 [veth]
>    veth_poll+0x139/0x571 [veth]
>    __napi_poll+0xa1/0x440
>    napi_threaded_poll+0x3d1/0x460
>    kthread+0x2a2/0x340
>    ret_from_fork+0x22/0x30
> 
> The buggy address belongs to the object at ffff888976250000
>    which belongs to the cache kmalloc-2k of size 2048
> The buggy address is located 340 bytes inside of
>    2048-byte region [ffff888976250000, ffff888976250800)
> 
> The buggy address belongs to the physical page:
> page:00000000ae18262a refcount:2 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x976250
> head:00000000ae18262a order:3 compound_mapcount:0 compound_pincount:0
> flags: 0x2ffff800010200(slab|head|node=0|zone=2|lastcpupid=0x1ffff)
> raw: 002ffff800010200 0000000000000000 dead000000000122 ffff88810004cf00
> raw: 0000000000000000 0000000080080008 00000002ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>    ffff888976250000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>    ffff888976250080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ffff888976250100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                    ^
>    ffff888976250180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>    ffff888976250200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> 
> Fixes: 718a18a0c8a6 ("veth: Rework veth_xdp_rcv_skb in order to accept non-linear skb")
> Signed-off-by: Shawn Bohrer <sbohrer@...udflare.com>

Acked-by: Toshiaki Makita <toshiaki.makita1@...il.com>