linux-kernel - Re: [PATCH bpf 1/2] bpf: Do not copy spin lock field from user in bpf_selem

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Message-ID: <fd1e6d2d-f7a2-21d2-f0ff-3e3d8b2ba9eb@huawei.com>
Date:   Wed, 16 Nov 2022 16:07:41 +0800
From:   Xu Kuohai <xukuohai@...wei.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH bpf 1/2] bpf: Do not copy spin lock field from user in
 bpf_selem_alloc

On 11/16/2022 1:27 PM, Alexei Starovoitov wrote:
> On Mon, Nov 14, 2022 at 5:31 AM Xu Kuohai <xukuohai@...wei.com> wrote:
>>
>> bpf_selem_alloc function is used by inode_storage, sk_storage and
>> task_storage maps to set map value, for these map types, there may
>> be a spin lock in the map value, so if we use memcpy to copy the whole
>> map value from user, the spin lock field may be initialized incorrectly.
>>
>> Since the spin lock field is zeroed by kzalloc, call copy_map_value
>> instead of memcpy to skip copying the spin lock field to fix it.
>>
>> Fixes: 6ac99e8f23d4 ("bpf: Introduce bpf sk local storage")
> 
> The tag is wrong. When local storage was introduced it was not
> possible to use spin_locks there.
> Pls resubmit.
> .

No, spin_lock was introduced by d83525ca62cf ("bpf: introduce bpf_spin_lock"),
before 6ac99e8f23d4 ("bpf: Introduce bpf sk local storage").

To confirm this, I built a kernel image on comit 6ac99e8f23d4 ("bpf: Introduce bpf sk local storage")
and run test case posted in patch 2, a softlockup was triggered. Then I picked
this patch and tried again, nothing failed.