diff mbox series

[v6,11/12] sched.h: extend task comm from 16 to 24

Message ID 20211025083315.4752-12-laoar.shao@gmail.com (mailing list archive)
State New
Headers show
Series extend task comm from 16 to 24 | expand

Commit Message

Yafang Shao Oct. 25, 2021, 8:33 a.m. UTC
When I was implementing a new per-cpu kthread cfs_migration, I found the
comm of it "cfs_migration/%u" is truncated due to the limitation of
TASK_COMM_LEN. For example, the comm of the percpu thread on CPU10~19 are
all with the same name "cfs_migration/1", which will confuse the user. This
issue is not critical, because we can get the corresponding CPU from the
task's Cpus_allowed. But for kthreads correspoinding to other hardware
devices, it is not easy to get the detailed device info from task comm,
for example,

    jbd2/nvme0n1p2-
    xfs-reclaim/sdf

We can also shorten the name to work around this problem, but I find
there are so many truncated kthreads:

    rcu_tasks_kthre
    rcu_tasks_rude_
    rcu_tasks_trace
    poll_mpt3sas0_s
    ext4-rsv-conver
    xfs-reclaim/sd{a, b, c, ...}
    xfs-blockgc/sd{a, b, c, ...}
    xfs-inodegc/sd{a, b, c, ...}
    audit_send_repl
    ecryptfs-kthrea
    vfio-irqfd-clea
    jbd2/nvme0n1p2-
    ...

We should improve this problem fundamentally by extending comm size to
24 bytes. task_struct is growing rather regularly by 8 bytes.

After this change, the truncated kthreads listed above will be
displayed as:

    rcu_tasks_kthread
    rcu_tasks_rude_kthread
    rcu_tasks_trace_kthread
    poll_mpt3sas0_statu
    ext4-rsv-conversion
    xfs-reclaim/sdf1
    xfs-blockgc/sdf1
    xfs-inodegc/sdf1
    audit_send_reply
    ecryptfs-kthread
    vfio-irqfd-cleanup
    jbd2/nvme0n1p2-8

As we have converted all the unsafe copy of task comm to the safe one,
this change won't make any trouble to the kernel or the in-tree tools.
The safe one and unsafe one of comm copy as follows,

  Unsafe                 Safe
  strlcpy                strscpy_pad
  strncpy                strscpy_pad
  bpf_probe_read_kernel  bpf_probe_read_kernel_str
                         bpf_core_read_str
                         bpf_get_current_comm
                         perf_event__prepare_comm
                         prctl(2)

Regarding the possible risk it may take to the out-of-tree user tools, if
the user tools get the task comm through kernel API like prctl(2),
bpf_get_current_comm() and etc, the tools still work well after this
change. While If the user tools get the task comm through direct string
copy, it must make sure the copied string should be with a nul terminator.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Petr Mladek <pmladek@suse.com>
---
 include/linux/sched.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Kees Cook Oct. 25, 2021, 9:30 p.m. UTC | #1
On Mon, Oct 25, 2021 at 08:33:14AM +0000, Yafang Shao wrote:
> When I was implementing a new per-cpu kthread cfs_migration, I found the
> comm of it "cfs_migration/%u" is truncated due to the limitation of
> TASK_COMM_LEN. For example, the comm of the percpu thread on CPU10~19 are
> all with the same name "cfs_migration/1", which will confuse the user. This
> issue is not critical, because we can get the corresponding CPU from the
> task's Cpus_allowed. But for kthreads correspoinding to other hardware
> devices, it is not easy to get the detailed device info from task comm,
> for example,
> 
>     jbd2/nvme0n1p2-
>     xfs-reclaim/sdf
> 
> We can also shorten the name to work around this problem, but I find
> there are so many truncated kthreads:
> 
>     rcu_tasks_kthre
>     rcu_tasks_rude_
>     rcu_tasks_trace
>     poll_mpt3sas0_s
>     ext4-rsv-conver
>     xfs-reclaim/sd{a, b, c, ...}
>     xfs-blockgc/sd{a, b, c, ...}
>     xfs-inodegc/sd{a, b, c, ...}
>     audit_send_repl
>     ecryptfs-kthrea
>     vfio-irqfd-clea
>     jbd2/nvme0n1p2-
>     ...
> 
> We should improve this problem fundamentally by extending comm size to
> 24 bytes. task_struct is growing rather regularly by 8 bytes.
> 
> After this change, the truncated kthreads listed above will be
> displayed as:
> 
>     rcu_tasks_kthread
>     rcu_tasks_rude_kthread
>     rcu_tasks_trace_kthread
>     poll_mpt3sas0_statu
>     ext4-rsv-conversion
>     xfs-reclaim/sdf1
>     xfs-blockgc/sdf1
>     xfs-inodegc/sdf1
>     audit_send_reply
>     ecryptfs-kthread
>     vfio-irqfd-cleanup
>     jbd2/nvme0n1p2-8
> 
> As we have converted all the unsafe copy of task comm to the safe one,
> this change won't make any trouble to the kernel or the in-tree tools.
> The safe one and unsafe one of comm copy as follows,
> 
>   Unsafe                 Safe
>   strlcpy                strscpy_pad
>   strncpy                strscpy_pad
>   bpf_probe_read_kernel  bpf_probe_read_kernel_str
>                          bpf_core_read_str
>                          bpf_get_current_comm
>                          perf_event__prepare_comm
>                          prctl(2)
> 
> Regarding the possible risk it may take to the out-of-tree user tools, if
> the user tools get the task comm through kernel API like prctl(2),
> bpf_get_current_comm() and etc, the tools still work well after this
> change. While If the user tools get the task comm through direct string
> copy, it must make sure the copied string should be with a nul terminator.
> 
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Petr Mladek <pmladek@suse.com>
> ---
>  include/linux/sched.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 124538db792c..490d12eabe44 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -279,7 +279,7 @@ struct task_group;
>   * BPF programs.
>   */
>  enum {
> -	TASK_COMM_LEN = 16,
> +	TASK_COMM_LEN = 24,
>  };

I suspect this should be kept in sync with the tools/ copy of sched.h
(i.e. we may need to keep the TASK_COMM_LEN_16 around in the kernel tree
too.)

>  
>  extern void scheduler_tick(void);
> -- 
> 2.17.1
>
Yafang Shao Oct. 26, 2021, 2:22 a.m. UTC | #2
On Tue, Oct 26, 2021 at 5:30 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Mon, Oct 25, 2021 at 08:33:14AM +0000, Yafang Shao wrote:
> > When I was implementing a new per-cpu kthread cfs_migration, I found the
> > comm of it "cfs_migration/%u" is truncated due to the limitation of
> > TASK_COMM_LEN. For example, the comm of the percpu thread on CPU10~19 are
> > all with the same name "cfs_migration/1", which will confuse the user. This
> > issue is not critical, because we can get the corresponding CPU from the
> > task's Cpus_allowed. But for kthreads correspoinding to other hardware
> > devices, it is not easy to get the detailed device info from task comm,
> > for example,
> >
> >     jbd2/nvme0n1p2-
> >     xfs-reclaim/sdf
> >
> > We can also shorten the name to work around this problem, but I find
> > there are so many truncated kthreads:
> >
> >     rcu_tasks_kthre
> >     rcu_tasks_rude_
> >     rcu_tasks_trace
> >     poll_mpt3sas0_s
> >     ext4-rsv-conver
> >     xfs-reclaim/sd{a, b, c, ...}
> >     xfs-blockgc/sd{a, b, c, ...}
> >     xfs-inodegc/sd{a, b, c, ...}
> >     audit_send_repl
> >     ecryptfs-kthrea
> >     vfio-irqfd-clea
> >     jbd2/nvme0n1p2-
> >     ...
> >
> > We should improve this problem fundamentally by extending comm size to
> > 24 bytes. task_struct is growing rather regularly by 8 bytes.
> >
> > After this change, the truncated kthreads listed above will be
> > displayed as:
> >
> >     rcu_tasks_kthread
> >     rcu_tasks_rude_kthread
> >     rcu_tasks_trace_kthread
> >     poll_mpt3sas0_statu
> >     ext4-rsv-conversion
> >     xfs-reclaim/sdf1
> >     xfs-blockgc/sdf1
> >     xfs-inodegc/sdf1
> >     audit_send_reply
> >     ecryptfs-kthread
> >     vfio-irqfd-cleanup
> >     jbd2/nvme0n1p2-8
> >
> > As we have converted all the unsafe copy of task comm to the safe one,
> > this change won't make any trouble to the kernel or the in-tree tools.
> > The safe one and unsafe one of comm copy as follows,
> >
> >   Unsafe                 Safe
> >   strlcpy                strscpy_pad
> >   strncpy                strscpy_pad
> >   bpf_probe_read_kernel  bpf_probe_read_kernel_str
> >                          bpf_core_read_str
> >                          bpf_get_current_comm
> >                          perf_event__prepare_comm
> >                          prctl(2)
> >
> > Regarding the possible risk it may take to the out-of-tree user tools, if
> > the user tools get the task comm through kernel API like prctl(2),
> > bpf_get_current_comm() and etc, the tools still work well after this
> > change. While If the user tools get the task comm through direct string
> > copy, it must make sure the copied string should be with a nul terminator.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> > Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
> > Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Cc: Al Viro <viro@zeniv.linux.org.uk>
> > Cc: Kees Cook <keescook@chromium.org>
> > Cc: Petr Mladek <pmladek@suse.com>
> > ---
> >  include/linux/sched.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 124538db792c..490d12eabe44 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -279,7 +279,7 @@ struct task_group;
> >   * BPF programs.
> >   */
> >  enum {
> > -     TASK_COMM_LEN = 16,
> > +     TASK_COMM_LEN = 24,
> >  };
>
> I suspect this should be kept in sync with the tools/ copy of sched.h
> (i.e. we may need to keep the TASK_COMM_LEN_16 around in the kernel tree
> too.)
>

Sure. I will change it.

> >
> >  extern void scheduler_tick(void);
> > --
> > 2.17.1
> >
>
> --
> Kees Cook
diff mbox series

Patch

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 124538db792c..490d12eabe44 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -279,7 +279,7 @@  struct task_group;
  * BPF programs.
  */
 enum {
-	TASK_COMM_LEN = 16,
+	TASK_COMM_LEN = 24,
 };
 
 extern void scheduler_tick(void);