Re: [PATCH v2] bpf: fix NULL pointer dereference in print_reg_state()

[Brahmajit Das]

On 26.09.2025 18:36, KaFai Wan wrote:
> On Fri, 2025-09-26 at 06:34 +0530, Brahmajit Das wrote:
> > On 25.09.2025 23:31, KaFai Wan wrote:
> > > On Wed, 2025-09-24 at 23:58 +0530, Brahmajit Das wrote:
> > > > On 25.09.2025 01:38, KaFai Wan wrote:
> > > > > On Wed, 2025-09-24 at 21:10 +0530, Brahmajit Das wrote:
> > > > > > On 24.09.2025 09:32, Alexei Starovoitov wrote:
> > > > > > > On Wed, Sep 24, 2025 at 1:43 AM Brahmajit Das
> > > > > > > <listout@xxxxxxxxxxx>
> > > > > > > wrote:
> > > > > > > > 
> > > > > > > > Syzkaller reported a general protection fault due to a
> > > > > > > > NULL
> > > > > > > > pointer
> > > > > > > > dereference in print_reg_state() when accessing reg-
> > > > > > > > >map_ptr
> > > > > > > > without
> > > > > > > > checking if it is NULL.
> > > > > > > > 
...snip...
> 
> You should add a Fixes label in the commit log and add selftest for it
> in V3. 
> Fixes label is Fixes: aced132599b3 ("bpf: Add range tracking for
> BPF_NEG")
> For selftest you may check the test in verifier_value_illegal_alu.c and
> other files.  
> 
> The code in your next post would change the behavior of BPF_NEG and 
> BPF_END, you can run the selftest to check that.
> 

KaFai, I'm quite new to kernel development. I'm been trying to write a
selftest for this unfortunately been having a hard time. I would really
appreciate some help. For now I tried to create on from the initial test
you used to verify this bug i.e. r0 -= r0.

I have tried testing my changes via sending a pull request on the
kernel-patches/bpf repository, but seems like it's failing.
My pull request: https://github.com/kernel-patches/bpf/pull/9900

-- 
Regards,
listout