netdev - Re: [PATCH v5] skbuff: Fix a race between coalescing and releasing SKBs

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Date:   Thu, 13 Apr 2023 19:42:19 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Liang Chen <liangchen.linux@...il.com>, <kuba@...nel.org>,
        <ilias.apalodimas@...aro.org>, <edumazet@...gle.com>,
        <hawk@...nel.org>
CC:     <netdev@...r.kernel.org>, <davem@...emloft.net>,
        <pabeni@...hat.com>, <alexander.duyck@...il.com>
Subject: Re: [PATCH v5] skbuff: Fix a race between coalescing and releasing
 SKBs

On 2023/4/13 17:03, Liang Chen wrote:
> Commit 1effe8ca4e34 ("skbuff: fix coalescing for page_pool fragment
> recycling") allowed coalescing to proceed with non page pool page and page
> pool page when @from is cloned, i.e.
> 
> to->pp_recycle    --> false
> from->pp_recycle  --> true
> skb_cloned(from)  --> true
> 
> However, it actually requires skb_cloned(@from) to hold true until
> coalescing finishes in this situation. If the other cloned SKB is
> released while the merging is in process, from_shinfo->nr_frags will be
> set to 0 toward the end of the function, causing the increment of frag
> page _refcount to be unexpectedly skipped resulting in inconsistent
> reference counts. Later when SKB(@to) is released, it frees the page
> directly even though the page pool page is still in use, leading to
> use-after-free or double-free errors. So it should be prohibited.
> 
> The double-free error message below prompted us to investigate:
> BUG: Bad page state in process swapper/1  pfn:0e0d1
> page:00000000c6548b28 refcount:-1 mapcount:0 mapping:0000000000000000
> index:0x2 pfn:0xe0d1
> flags: 0xfffffc0000000(node=0|zone=1|lastcpupid=0x1fffff)
> raw: 000fffffc0000000 0000000000000000 ffffffff00000101 0000000000000000
> raw: 0000000000000002 0000000000000000 ffffffffffffffff 0000000000000000
> page dumped because: nonzero _refcount
> 
> CPU: 1 PID: 0 Comm: swapper/1 Tainted: G            E      6.2.0+
> Call Trace:
>  <IRQ>
> dump_stack_lvl+0x32/0x50
> bad_page+0x69/0xf0
> free_pcp_prepare+0x260/0x2f0
> free_unref_page+0x20/0x1c0
> skb_release_data+0x10b/0x1a0
> napi_consume_skb+0x56/0x150
> net_rx_action+0xf0/0x350
> ? __napi_schedule+0x79/0x90
> __do_softirq+0xc8/0x2b1
> __irq_exit_rcu+0xb9/0xf0
> common_interrupt+0x82/0xa0
> </IRQ>
> <TASK>
> asm_common_interrupt+0x22/0x40
> RIP: 0010:default_idle+0xb/0x20
> 
> Fixes: 53e0961da1c7 ("page_pool: add frag page recycling support in page pool")

I am not quite sure the above is right Fixes tag.
As 1effe8ca4e34 ("skbuff: fix coalescing for page_pool fragment recycling") has tried
to fix it, and it missed the case this patch is fixing, so we need another fix here.