netdev - Re: [PATCH net] sctp: check asoc strreset_chunk in sctp_generate_reconf

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Date:   Sat, 23 Apr 2022 10:18:02 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        davem@...emloft.net, kuba@...nel.org,
        Neil Horman <nhorman@...driver.com>
Subject: Re: [PATCH net] sctp: check asoc strreset_chunk in
 sctp_generate_reconf_event

On Wed, Apr 20, 2022 at 04:52:41PM -0400, Xin Long wrote:
> A null pointer reference issue can be triggered when the response of a
> stream reconf request arrives after the timer is triggered, such as:
> 
>   send Incoming SSN Reset Request --->
>   CPU0:
>    reconf timer is triggered,
>    go to the handler code before hold sk lock
>                             <--- reply with Outgoing SSN Reset Request
>   CPU1:
>    process Outgoing SSN Reset Request,
>    and set asoc->strreset_chunk to NULL
>   CPU0:
>    continue the handler code, hold sk lock,
>    and try to hold asoc->strreset_chunk, crash!
> 
> In Ying Xu's testing, the call trace is:
> 
>   [ ] BUG: kernel NULL pointer dereference, address: 0000000000000010
>   [ ] RIP: 0010:sctp_chunk_hold+0xe/0x40 [sctp]
>   [ ] Call Trace:
>   [ ]  <IRQ>
>   [ ]  sctp_sf_send_reconf+0x2c/0x100 [sctp]
>   [ ]  sctp_do_sm+0xa4/0x220 [sctp]
>   [ ]  sctp_generate_reconf_event+0xbd/0xe0 [sctp]
>   [ ]  call_timer_fn+0x26/0x130
> 
> This patch is to fix it by returning from the timer handler if asoc
> strreset_chunk is already set to NULL.

Right. The timer callback didn't have a check on whether it was still
needed or not, and per the description above, it would simply try to
handle it twice then.

> 
> Fixes: 7b9438de0cd4 ("sctp: add stream reconf timer")
> Reported-by: Ying Xu <yinxu@...hat.com>
> Signed-off-by: Xin Long <lucien.xin@...il.com>

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>