linux-kernel - Re: [PATCH bpf v2] libbpf: fix passing uninitialized bytes to setsockopt

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Message-ID: <c338b2fd-8e0d-885d-5895-317d20800815@ovn.org>
Date:   Sun, 13 Oct 2019 12:17:47 +0200
From:   Ilya Maximets <i.maximets@....org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Ilya Maximets <i.maximets@....org>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S . Miller" <davem@...emloft.net>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Subject: Re: [PATCH bpf v2] libbpf: fix passing uninitialized bytes to
 setsockopt

On 13.10.2019 1:24, Alexei Starovoitov wrote:
> On Wed, Oct 09, 2019 at 06:49:29PM +0200, Ilya Maximets wrote:
>> 'struct xdp_umem_reg' has 4 bytes of padding at the end that makes
>> valgrind complain about passing uninitialized stack memory to the
>> syscall:
>>
>>    Syscall param socketcall.setsockopt() points to uninitialised byte(s)
>>      at 0x4E7AB7E: setsockopt (in /usr/lib64/libc-2.29.so)
>>      by 0x4BDE035: xsk_umem__create@@LIBBPF_0.0.4 (xsk.c:172)
>>    Uninitialised value was created by a stack allocation
>>      at 0x4BDDEBA: xsk_umem__create@@LIBBPF_0.0.4 (xsk.c:140)
>>
>> Padding bytes appeared after introducing of a new 'flags' field.
>> memset() is required to clear them.
>>
>> Fixes: 10d30e301732 ("libbpf: add flags to umem config")
>> Signed-off-by: Ilya Maximets <i.maximets@....org>
>> ---
>>
>> Version 2:
>>    * Struct initializer replaced with explicit memset(). [Andrii]
>>
>>   tools/lib/bpf/xsk.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
>> index a902838f9fcc..9d5348086203 100644
>> --- a/tools/lib/bpf/xsk.c
>> +++ b/tools/lib/bpf/xsk.c
>> @@ -163,6 +163,7 @@ int xsk_umem__create_v0_0_4(struct xsk_umem **umem_ptr, void *umem_area,
>>   	umem->umem_area = umem_area;
>>   	xsk_set_umem_config(&umem->config, usr_config);
>>   
>> +	memset(&mr, 0, sizeof(mr));
>>   	mr.addr = (uintptr_t)umem_area;
>>   	mr.len = size;
>>   	mr.chunk_size = umem->config.frame_size;
> 
> This was already applied. Why did you resend?
> 

Sorry, it wasn't me.  Looking at the mail delivery chain:

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There is some strange server listssympa-test.colorado.edu.
Looks like someone in colorado.edu is testing stuff on production server.

The simplified delivery chain looks like this:

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Best regards, Ilya Maximets.