netdev - Re: [PATCH net 1/1] net sched actions: fix dumping which requires several messages to user space

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Date:   Tue, 27 Mar 2018 07:26:16 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Craig Dillabaugh <cdillaba@...atatu.com>, davem@...emloft.net
Cc:     netdev@...r.kernel.org, kernel@...atatu.com,
        xiyou.wangcong@...il.com, jiri@...nulli.us
Subject: Re: [PATCH net 1/1] net sched actions: fix dumping which requires
 several messages to user space

On 18-03-26 02:58 PM, Craig Dillabaugh wrote:
>      Fixes a bug in the tcf_dump_walker function that can cause some actions
>      to not be reported when dumping a large number of actions. This issue
>      became more aggrevated when cookies feature was added. In particular
>      this issue is manifest when large cookie values are assigned to the
>      actions and when enough actions are created that the resulting table
>      must be dumped in multiple batches.
> 
>      The number of actions returned in each batch is limited by the total
>      number of actions and the memory buffer size.  With small cookies
>      the numeric limit is reached before the buffer size limit, which avoids
>      the code path triggering this bug. When large cookies are used buffer
>      fills before the numeric limit, and the erroneous code path is hit.
> 
>      For example after creating 32 csum actions with the cookie
>      aaaabbbbccccdddd
> 
>      $ tc actions ls action csum
>      total acts 26
> 
>          action order 0: csum (tcp) action continue
>          index 1 ref 1 bind 0
>          cookie aaaabbbbccccdddd
> 
>          .....
> 
>          action order 25: csum (tcp) action continue
>          index 26 ref 1 bind 0
>          cookie aaaabbbbccccdddd
>      total acts 6
> 
>          action order 0: csum (tcp) action continue
>          index 28 ref 1 bind 0
>          cookie aaaabbbbccccdddd
> 
>          ......
> 
>          action order 5: csum (tcp) action continue
>          index 32 ref 1 bind 0
>          cookie aaaabbbbccccdddd
> 
>      Note that the action with index 27 is omitted from the report.
> 
> Fixes: 4b3550ef530c ("[NET_SCHED]: Use nla_nest_start/nla_nest_end")"
> Signed-off-by: Craig Dillabaugh <cdillaba@...atatu.com>

Good catch.
Acked-by: Jamal Hadi Salim <jhs@...atatu.com>

cheers,
jamal