netdev - Re: [PATCH net 3/3] net: strparser: partially revert "strparser: Call skb

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Date:   Wed, 10 Apr 2019 12:40:36 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>, davem@...emloft.net
Cc:     oss-drivers@...ronome.com, netdev@...r.kernel.org,
        alexei.starovoitov@...il.com, vakul.garg@....com,
        borisp@...lanox.com,
        Dirk van der Merwe <dirk.vandermerwe@...ronome.com>
Subject: Re: [PATCH net 3/3] net: strparser: partially revert "strparser: Call
 skb_unclone conditionally"



On 04/10/2019 11:04 AM, Jakub Kicinski wrote:
> This reverts the first part of commit 4e485d06bb8c ("strparser: Call
> skb_unclone conditionally").  To build a message with multiple
> fragments we need our own root of frag_list.  We can't simply
> use the frag_list of orig_skb, because it will lead to linking
> all orig_skbs together creating very long frag chains, and causing
> stack overflow on kfree_skb() (which is called recursively on
> the frag_lists).
> 
> BUG: stack guard page was hit at 00000000d40fad41 (stack is 0000000029dde9f4..000000008cce03d5)
> kernel stack overflow (double-fault): 0000 [#1] PREEMPT SMP
> RIP: 0010:free_one_page+0x2b/0x490
> 
> Call Trace:
>   __free_pages_ok+0x143/0x2c0
>   skb_release_data+0x8e/0x140
>   ? skb_release_data+0xad/0x140
>   kfree_skb+0x32/0xb0
> 
>   [...]
> 
>   skb_release_data+0xad/0x140
>   ? skb_release_data+0xad/0x140

...

>   tcp_disconnect+0xd6/0x4d0
>   tcp_close+0xf4/0x430
>   ? tcp_check_oom+0xf0/0xf0
>   tls_sk_proto_close+0xe4/0x1e0 [tls]
>   inet_release+0x36/0x60
>   __sock_release+0x37/0xa0
>   sock_close+0x11/0x20
>   __fput+0xa2/0x1d0
>   task_work_run+0x89/0xb0
>   exit_to_usermode_loop+0x9a/0xa0
>   do_syscall_64+0xc0/0xf0
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Let's leave the second unclone conditional, as I'm not entirely
> sure what is its purpose :)
> 
> Fixes: 4e485d06bb8c ("strparser: Call skb_unclone conditionally")
> Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
> Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@...ronome.com>

Thanks for tracking the root cause of this problem.

Reviewed-by: Eric Dumazet <edumazet@...gle.com>