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

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Date:   Mon, 21 Nov 2022 11:50:49 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Xu Kuohai <xukuohai@...weicloud.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 Mon, Nov 21, 2022 at 3:30 AM Xu Kuohai <xukuohai@...weicloud.com> wrote:
>
> On 11/16/2022 4:07 PM, Xu Kuohai wrote:
> > 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.
>
> Hello, am I right? Or could you please give the correct fix-tag? Thanks.

I see. I was under the impression that bpf_spin_lock was enabled
in the local storage later.
Ok. Applied as-is.