netdev - Re: [PATCH 1/2] bpf: sockmap, fix uninitialized variable

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Date:   Thu, 17 May 2018 13:12:43 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] bpf: sockmap, fix uninitialized variable

Hi John,

On 05/17/2018 12:27 PM, John Fastabend wrote:
> On 05/17/2018 07:08 AM, Gustavo A. R. Silva wrote:
>> There is a potential execution path in which variable err is
>> returned without being properly initialized previously.
>>
>> Fix this by initializing variable err to 0.
>>
>> Addresses-Coverity-ID: 1468964 ("Uninitialized scalar variable")
>> Fixes: e5cd3abcb31a ("bpf: sockmap, refactor sockmap routines to work
>> with hashmap")
>> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
>> ---
>>   kernel/bpf/sockmap.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
>> index c6de139..41b41fc 100644
>> --- a/kernel/bpf/sockmap.c
>> +++ b/kernel/bpf/sockmap.c
>> @@ -1713,7 +1713,7 @@ static int __sock_map_ctx_update_elem(struct bpf_map *map,
>>   	struct smap_psock_map_entry *e = NULL;
>>   	struct smap_psock *psock;
>>   	bool new = false;
>> -	int err;
>> +	int err = 0;
>>   
>>   	/* 1. If sock map has BPF programs those will be inherited by the
>>   	 * sock being added. If the sock is already attached to BPF programs
>>
> 
> Thanks for catching this and the quick fix. The path to hit this case
> is to add a sock to a map (without a BPF program) where the sock already
> has been added to another map. I don't have any tests for the case with
> socks in multiple maps so I'll add some to the selftests so I remember
> this case.
> 

Glad to help. :)

> The alternative fix would be to always 'return 0' at the end of the
> function, but I think its probably better to init err here like above.
> 

Yeah. I think initializing err is better in this case.

> Acked-by: John Fastabend <john.fastabend@...il.com>
> 

Thank you
--
Gustavo