netdev - Re: [PATCH net] ipv4: ensure rcu_read_lock() in ipv4_link

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Message-ID: <dbd29397-719d-f0d0-09a7-3ec6afb0d5b7@gmail.com>
Date:   Sun, 14 Apr 2019 15:32:59 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>, edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        syzkaller@...glegroups.com, ssuryaextr@...il.com
Subject: Re: [PATCH net] ipv4: ensure rcu_read_lock() in ipv4_link_failure()



On 04/14/2019 01:44 PM, David Miller wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> Date: Sat, 13 Apr 2019 17:32:21 -0700
> 
>> fib_compute_spec_dst() needs to be called under rcu protection.
>>
>> syzbot reported :
>  ...
>> Fixes: ed0de45a1008 ("ipv4: recompile ip options in ipv4_link_failure")
>> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>> Reported-by: syzbot <syzkaller@...glegroups.com>
> 
> Applied, thanks Eric.
> 
> Please take a look at the cipso_v4_error case.
> 

I am not familiar of this code, but it looks like it runs from BH rx handler,
with rcu_read_lock() asserted.

The problem for ipv4_link_failure() is that it can be run from a timer handler,
which does not generally hold rcu_read_lock().