netdev - Re: [PATCH net-next] ipv4: Fix refcount warning for new fib

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Date:   Mon, 2 Aug 2021 12:04:01 -0600
From:   David Ahern <dsahern@...il.com>
To:     Matthieu Baerts <matthieu.baerts@...sares.net>,
        David Ahern <dsahern@...nel.org>
Cc:     ciorneiioana@...il.com, Yajun Deng <yajun.deng@...ux.dev>,
        netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org
Subject: Re: [PATCH net-next] ipv4: Fix refcount warning for new fib_info

On 8/2/21 11:58 AM, Matthieu Baerts wrote:
> Hi David,
> 
> On 02/08/2021 18:02, David Ahern wrote:
>> Ioana reported a refcount warning when booting over NFS:
>>
>> [    5.042532] ------------[ cut here ]------------
>> [    5.047184] refcount_t: addition on 0; use-after-free.
>> [    5.052324] WARNING: CPU: 7 PID: 1 at lib/refcount.c:25 refcount_warn_saturate+0xa4/0x150
>> ...
>> [    5.167201] Call trace:
>> [    5.169635]  refcount_warn_saturate+0xa4/0x150
>> [    5.174067]  fib_create_info+0xc00/0xc90
>> [    5.177982]  fib_table_insert+0x8c/0x620
>> [    5.181893]  fib_magic.isra.0+0x110/0x11c
>> [    5.185891]  fib_add_ifaddr+0xb8/0x190
>> [    5.189629]  fib_inetaddr_event+0x8c/0x140
>>
>> fib_treeref needs to be set after kzalloc. The old code had a ++ which
>> led to the confusion when the int was replaced by a refcount_t.
> 
> Thank you for the patch!
> 
> My CI was also complaining of not being able to run kernel selftests [1].
> Your patch fixes the issue, thanks!
> 
> Tested-by: Matthieu Baerts <matthieu.baerts@...sares.net>
> 

Given how easily it is to trigger the warning, I get the impression the
original was an untested patch.