Re: [PATCH] riscv: Fix a NULL pointer reference in machine_kexec_prepare

[Pratyush Yadav <pratyush@kernel.org>]

On Wed, Jul 01 2026, Tao Liu wrote:

> Hi Pratyush,
>
> On Mon, Jun 29, 2026 at 11:13 PM Pratyush Yadav <pratyush@kernel.org> wrote:
>>
>> +Cc IMA maintainers
>>
>> On Fri, Jun 26 2026, Baoquan He wrote:
>>
>> > Add kexec ML to CC.
>> >
>> > On Fri, Jun 26, 2026 at 7:46 AM Tao Liu <ltao@redhat.com> wrote:
>> >>
>> >> Kindly ping, any comments?
>> >>
>> >> Thanks,
>> >> Tao Liu
>> >>
>> >> On Fri, May 29, 2026 at 3:35 PM Tao Liu <ltao@redhat.com> wrote:
>> >> >
>> >> > A NULL pointer reference issue is noticed in riscv's machine_kexec_prepare,
>> >> > where image->segment[i].buf might be NULL and copied unchecked.
>> >> >
>> >> > The NULL buf comes from security/integrity/ima/ima_kexec.c:
>> >> > ima_add_kexec_buffer(), where kbuf is added by kexec_add_buffer(),
>> >> > but kbuf.buffer is NULL.
>> >> >
>> >> > Fix this by simply adding a check before copy.
>> >> >
>> >> > Signed-off-by: Tao Liu <ltao@redhat.com>
>> >> > ---
>> >> >  arch/riscv/kernel/machine_kexec.c | 3 +++
>> >> >  1 file changed, 3 insertions(+)
>> >> >
>> >> > diff --git a/arch/riscv/kernel/machine_kexec.c b/arch/riscv/kernel/machine_kexec.c
>> >> > index 2306ce3e5f22..d81d576f9cb5 100644
>> >> > --- a/arch/riscv/kernel/machine_kexec.c
>> >> > +++ b/arch/riscv/kernel/machine_kexec.c
>> >> > @@ -41,6 +41,9 @@ machine_kexec_prepare(struct kimage *image)
>> >> >                 if (image->segment[i].memsz <= sizeof(fdt))
>> >> >                         continue;
>> >> >
>> >> > +               if (image->segment[i].buf == NULL)
>> >> > +                       continue;
>> >> > +
>> >
>> > This is a good fix, maybe we can add code comments to explain it as
>> > below, just for reference.
>> >
>> >                /*
>> >                 * Some segments (e.g. IMA) reserve space but have no buffer
>> >                 * loaded yet. Skip them as they cannot contain an FDT.
>> >                 */
>> > And is there any other place where the similar issue exists? e.g on LoongArch?
>> >
>> > Other than above concerns, this patch looks good to me:
>> >
>> > Acked-by: Baoquan He <bhe@redhat.com>
>>
>> Yeah, the patch LGTM to me too.
>>
>> Acked-by: Pratyush Yadav <pratyush@kernel.org>
>>
>> Although I think IMA can make this a bit easier to understand. First, in
>> ima_add_kexec_buffer() it should set kbuf.buffer to NULL and kbuf.bufsz
>> to 0 explicitly instead of using kexec_buffer and kexec_buffer_size
>> which are initialized to NULL and 0, but never updated. Using the
>> variables here adds an extra level of indirection.
>>
>> Also, perhaps we should add a comment in ima_add_kexec_buffer() about
>> how this all works, since where the IMA buffer lives and where it gets
>> updated it fairly complicated and took me some time to piece together.
>
> Thanks for your patch review and suggestions! I agree with your point
> on the IMA part, I was confused by the code too, e.g in
> ima_add_kexec_buffer():
>
> void *kexec_buffer = NULL;
> kbuf.buffer = kexec_buffer;
> ret = kexec_add_buffer(&kbuf);
> if (ret) {
>     pr_err("Error passing over kexec measurement buffer.\n");
>     vfree(kexec_buffer);
>     return;
> }
>
> Do we need to vfree(kexec_buffer)? When kexec_buffer is NULL and seems
> never get updated.
>
> I'm not familiar with IMA code, maybe there is a reason which I'm unaware of...

I think it is just leftover from refactors. kexec_buffer used to point
to an actual buffer at some point and refactors to the function left
them always NULL but never removed them.

-- 
Regards,
Pratyush Yadav