linux-kernel - Re: [PATCH] pid: Add the judgment of whether ns is NULL in the find_pid

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Date:   Wed, 26 Jul 2023 09:23:13 +0800
From:   Xuewen Yan <xuewen.yan94@...il.com>
To:     Christian Brauner <brauner@...nel.org>
Cc:     Xuewen Yan <xuewen.yan@...soc.com>, jack@...e.cz,
        keescook@...omium.org, peterz@...radead.org,
        vincent.guittot@...aro.org, linux-kernel@...r.kernel.org,
        di.shen@...soc.com
Subject: Re: [PATCH] pid: Add the judgment of whether ns is NULL in the find_pid_ns

On Tue, Jul 25, 2023 at 8:47 PM Christian Brauner <brauner@...nel.org> wrote:
>
> On Tue, Jul 25, 2023 at 08:24:18PM +0800, Xuewen Yan wrote:
> > On Tue, Jul 25, 2023 at 4:49 PM Christian Brauner <brauner@...nel.org> wrote:
> > >
> > > On Thu, Jul 13, 2023 at 03:17:13PM +0800, Xuewen Yan wrote:
> > > > There is no the judgment of whether namspace is NULL in find_pid_ns.
> > > > But there is a corner case when ns is null, for example: if user
> > > > call find_get_pid when current is in exiting, the following stack would
> > > > set thread_id be null:
> > > > release_task
> > > >     __exit_signal(p);
> > > >         __unhash_process(tsk, group_dead);
> > > >               detach_pid(p, PIDTYPE_PID);
> > > >                   __change_pid(task, type, NULL);
> > > >
> > > > If user call find_get_pid at now, in find_vpid function, the
> > >
> > > I fail to see how this can happen. The code you're referencing is in
> > > release_task(). If current has gone through that then current obviously
> > > can't call find_vpid() on itself anymore or anything else for that
> > > matter.
> >
> > This happened when user calls  find_vpid() in irq.
> >
> > [72117.635162] Call trace:
> > [72117.635595]  idr_find+0xc/0x24
> > [72117.636103]  find_get_pid+0x40/0x68
> > [72117.636812]  send_event+0x88/0x180 [demux]
> > [72117.637593]  vbvop_copy_data+0x150/0x344 [demux]
> > [72117.638434]  dmisr_video_parsing_mpeg12+0x29c/0x42c [demux]
> > [72117.639393]  dmisr_video_parsing_switch+0x68/0xec [demux]
> > [72117.640332]  dmisr_handle_video_pes+0x10c/0x26c [demux]
> > [72117.641108]  tasklet_action_common+0x130/0x224
> > [72117.641784]  tasklet_action+0x28/0x34
> > [72117.642366]  __do_softirq+0x128/0x4dc
> > [72117.642944]  irq_exit+0xf8/0xfc
> > [72117.643459]  __handle_domain_irq+0xb0/0x108
> > [72117.644102]  gic_handle_irq+0x6c/0x124
> > [72117.644691]  el1_irq+0x108/0x200
> > [72117.645217]  _raw_write_unlock_irq+0x2c/0x5c
> > [72117.645870]  release_task+0x144/0x1ac   <<<<<<
> > [72117.646447]  do_exit+0x524/0x94c
> > [72117.646970]  __do_sys_exit_group+0x0/0x14
> > [72117.647591]  do_group_exit+0x0/0xa0
> > [72117.648146]  __se_sys_exit+0x0/0x20
> > [72117.648704]  el0_svc_common+0xcc/0x1bc
> > [72117.649292]  el0_svc_handler+0x2c/0x3c
> > [72117.649881]  el0_svc+0x8/0xc
> >
> > In release_task, write_unlock_irq(&tasklist_lock) will open irq, at
> > this time, if user calls find_get_pid() in irq, because
> > current->thread_id is NULL,
> > it will handle the NULL pointer.
>
> Uhm, where is that code from? This doesn't seem to be upstream.

It's from our own platform, we found someone called  find_get_pid() in
the module, and caused the crash.

BR