Re: [PATCH bpf 1/2] bpf: Do not copy spin lock field from user in bpf_selem_alloc

[Xu Kuohai]

On 11/16/2022 1:27 PM, Alexei Starovoitov wrote:
> On Mon, Nov 14, 2022 at 5:31 AM Xu Kuohai <xukuohai@xxxxxxxxxx> 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.