linux-kernel - Re: [PATCH bpf-next 1/3] bpf: Make struct task

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20230331170504.umr5zmcraburmtkg@dhcp-172-26-102-232.dhcp.thefacebook.com>
Date:   Fri, 31 Mar 2023 10:05:04 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     David Vernet <void@...ifault.com>
Cc:     bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
        yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org,
        sdf@...gle.com, haoluo@...gle.com, jolsa@...nel.org,
        linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH bpf-next 1/3] bpf: Make struct task_struct an RCU-safe
 type

On Thu, Mar 30, 2023 at 07:57:31PM -0500, David Vernet wrote:
>  kernel/bpf/helpers.c                          | 11 ++-
>  kernel/bpf/verifier.c                         |  1 +
>  .../selftests/bpf/prog_tests/task_kfunc.c     |  2 +
>  .../selftests/bpf/progs/task_kfunc_common.h   |  5 +
>  .../selftests/bpf/progs/task_kfunc_failure.c  | 98 +++++++++++++++++--
>  .../selftests/bpf/progs/task_kfunc_success.c  | 52 +++++++++-
>  6 files changed, 153 insertions(+), 16 deletions(-)

See CI failures on gcc compiled kernel:
https://github.com/kernel-patches/bpf/actions/runs/4570493668/jobs/8068004031

>  __bpf_kfunc struct task_struct *bpf_task_acquire(struct task_struct *p)
>  {
> -	return get_task_struct(p);
> +	if (refcount_inc_not_zero(&p->rcu_users))
> +		return p;
> +	return NULL;
>  }

I wonder whether we should add a bit of safety net here.
Like do not allow acquire of tasks with PF_KTHREAD | PF_EXITING
or at least is_idle_task ?