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Message-ID: <20180712165415.GA16049@sec>
Date: Thu, 12 Jul 2018 16:54:16 +0000
From: Tyler Hicks <tyhicks@...onical.com>
To: Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
Cc: "David S . Miller" <davem@...emloft.net>,
Jesper Dangaard Brouer <brouer@...hat.com>,
netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: gro: properly remove skb from list
On 2018-07-12 16:24:59, Prashant Bhole wrote:
> Following crash occurs in validate_xmit_skb_list() when same skb is
> iterated multiple times in the loop and consume_skb() is called.
>
> The root cause is calling list_del_init(&skb->list) and not clearing
> skb->next in d4546c2509b1. list_del_init(&skb->list) sets skb->next
> to point to skb itself. skb->next needs to be cleared because other
> parts of network stack uses another kind of SKB lists.
> validate_xmit_skb_list() uses such list.
>
> A similar type of bugfix was reported by Jesper Dangaard Brouer.
> https://patchwork.ozlabs.org/patch/942541/
>
> This patch clears skb->next and changes list_del_init() to list_del()
> so that list->prev will maintain the list poison.
>
> [ 148.185511] ==================================================================
> [ 148.187865] BUG: KASAN: use-after-free in validate_xmit_skb_list+0x4b/0xa0
> [ 148.190158] Read of size 8 at addr ffff8801e52eefc0 by task swapper/1/0
> [ 148.192940]
> [ 148.193642] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.18.0-rc3+ #25
> [ 148.195423] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20180531_142017-buildhw-08.phx2.fedoraproject.org-1.fc28 04/01/2014
> [ 148.199129] Call Trace:
> [ 148.200565] <IRQ>
> [ 148.201911] dump_stack+0xc6/0x14c
> [ 148.203572] ? dump_stack_print_info.cold.1+0x2f/0x2f
> [ 148.205083] ? kmsg_dump_rewind_nolock+0x59/0x59
> [ 148.206307] ? validate_xmit_skb+0x2c6/0x560
> [ 148.207432] ? debug_show_held_locks+0x30/0x30
> [ 148.208571] ? validate_xmit_skb_list+0x4b/0xa0
> [ 148.211144] print_address_description+0x6c/0x23c
> [ 148.212601] ? validate_xmit_skb_list+0x4b/0xa0
> [ 148.213782] kasan_report.cold.6+0x241/0x2fd
> [ 148.214958] validate_xmit_skb_list+0x4b/0xa0
> [ 148.216494] sch_direct_xmit+0x1b0/0x680
> [ 148.217601] ? dev_watchdog+0x4e0/0x4e0
> [ 148.218675] ? do_raw_spin_trylock+0x10/0x120
> [ 148.219818] ? do_raw_spin_lock+0xe0/0xe0
> [ 148.221032] __dev_queue_xmit+0x1167/0x1810
> [ 148.222155] ? sched_clock+0x5/0x10
> [...]
>
> [ 148.474257] Allocated by task 0:
> [ 148.475363] kasan_kmalloc+0xbf/0xe0
> [ 148.476503] kmem_cache_alloc+0xb4/0x1b0
> [ 148.477654] __build_skb+0x91/0x250
> [ 148.478677] build_skb+0x67/0x180
> [ 148.479657] e1000_clean_rx_irq+0x542/0x8a0
> [ 148.480757] e1000_clean+0x652/0xd10
> [ 148.481772] net_rx_action+0x4ea/0xc20
> [ 148.482808] __do_softirq+0x1f9/0x574
> [ 148.483831]
> [ 148.484575] Freed by task 0:
> [ 148.485504] __kasan_slab_free+0x12e/0x180
> [ 148.486589] kmem_cache_free+0xb4/0x240
> [ 148.487634] kfree_skbmem+0xed/0x150
> [ 148.488648] consume_skb+0x146/0x250
> [ 148.489665] validate_xmit_skb+0x2b7/0x560
> [ 148.490754] validate_xmit_skb_list+0x70/0xa0
> [ 148.491897] sch_direct_xmit+0x1b0/0x680
> [ 148.493949] __dev_queue_xmit+0x1167/0x1810
> [ 148.495103] br_dev_queue_push_xmit+0xce/0x250
> [ 148.496196] br_forward_finish+0x276/0x280
> [ 148.497234] __br_forward+0x44f/0x520
> [ 148.498260] br_forward+0x19f/0x1b0
> [ 148.499264] br_handle_frame_finish+0x65e/0x980
> [ 148.500398] NF_HOOK.constprop.10+0x290/0x2a0
> [ 148.501522] br_handle_frame+0x417/0x640
> [ 148.502582] __netif_receive_skb_core+0xaac/0x18f0
> [ 148.503753] __netif_receive_skb_one_core+0x98/0x120
> [ 148.504958] netif_receive_skb_internal+0xe3/0x330
> [ 148.506154] napi_gro_complete+0x190/0x2a0
> [ 148.507243] dev_gro_receive+0x9f7/0x1100
> [ 148.508316] napi_gro_receive+0xcb/0x260
> [ 148.509387] e1000_clean_rx_irq+0x2fc/0x8a0
> [ 148.510501] e1000_clean+0x652/0xd10
> [ 148.511523] net_rx_action+0x4ea/0xc20
> [ 148.512566] __do_softirq+0x1f9/0x574
> [ 148.513598]
> [ 148.514346] The buggy address belongs to the object at ffff8801e52eefc0
> [ 148.514346] which belongs to the cache skbuff_head_cache of size 232
> [ 148.517047] The buggy address is located 0 bytes inside of
> [ 148.517047] 232-byte region [ffff8801e52eefc0, ffff8801e52ef0a8)
> [ 148.519549] The buggy address belongs to the page:
> [ 148.520726] page:ffffea000794bb00 count:1 mapcount:0 mapping:ffff880106f4dfc0 index:0xffff8801e52ee840 compound_mapcount: 0
> [ 148.524325] flags: 0x17ffffc0008100(slab|head)
> [ 148.525481] raw: 0017ffffc0008100 ffff880106b938d0 ffff880106b938d0 ffff880106f4dfc0
> [ 148.527503] raw: ffff8801e52ee840 0000000000190011 00000001ffffffff 0000000000000000
> [ 148.529547] page dumped because: kasan: bad access detected
>
> Fixes: d4546c2509b1 ("net: Convert GRO SKB handling to list_head.")
> Signed-off-by: Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
> Reported-by: Tyler Hicks <tyhicks@...onical.com>
Thanks for the fix! I have verified that it fixes the crash that I was
seeing.
Tested-by: Tyler Hicks <tyhicks@...onical.com>
Your analysis of the problem makes sense. I feel like a helper function
to properly remove an skb from list_head and NULL the next pointer, in
the GRO code, before passing it on to something else that uses the
hand-rolled linked list implementation could help with maintainability.
That's just a suggestion - this patch looks good to me:
Reviewed-by: Tyler Hicks <tyhicks@...onical.com>
Tyler
> ---
> net/core/dev.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index d13cddcac41f..08c41941f912 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -5169,7 +5169,8 @@ static void __napi_gro_flush_chain(struct napi_struct *napi, u32 index,
> list_for_each_entry_safe_reverse(skb, p, head, list) {
> if (flush_old && NAPI_GRO_CB(skb)->age == jiffies)
> return;
> - list_del_init(&skb->list);
> + list_del(&skb->list);
> + skb->next = NULL;
> napi_gro_complete(skb);
> napi->gro_count--;
> napi->gro_hash[index].count--;
> @@ -5350,7 +5351,8 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
> ret = NAPI_GRO_CB(skb)->free ? GRO_MERGED_FREE : GRO_MERGED;
>
> if (pp) {
> - list_del_init(&pp->list);
> + list_del(&pp->list);
> + pp->next = NULL;
> napi_gro_complete(pp);
> napi->gro_count--;
> napi->gro_hash[hash].count--;
> --
> 2.17.1
>
>
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