From: Yafang Shao <laoar.shao@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Kees Cook <keescook@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Valentin Schneider <valentin.schneider@arm.com>,
Qiang Zhang <qiang.zhang@windriver.com>,
robdclark <robdclark@chromium.org>,
christian <christian@brauner.io>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
David Miller <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>, Martin Lau <kafai@fb.com>,
Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
john fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
dennis.dalessandro@cornelisnetworks.com,
mike.marciniszyn@cornelisnetworks.com, dledford@redhat.com,
jgg@ziepe.ca, linux-rdma@vger.kernel.org,
netdev <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
"linux-perf-use." <linux-perf-users@vger.kernel.org>,
linux-fsdevel@vger.kernel.org, Linux MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
kernel test robot <oliver.sang@intel.com>,
kbuild test robot <lkp@intel.com>
Subject: Re: [PATCH v7 00/11] extend task comm from 16 to 24
Date: Mon, 1 Nov 2021 22:34:30 +0800 [thread overview]
Message-ID: <CALOAHbA61RyGVzG8SVcNG=0rdqnUCt4AxCKmtuxRnbS_SH=+MQ@mail.gmail.com> (raw)
In-Reply-To: <YX/0h7j/nDwoBA+J@alley>
On Mon, Nov 1, 2021 at 10:07 PM Petr Mladek <pmladek@suse.com> wrote:
>
> On Mon 2021-11-01 06:04:08, Yafang Shao wrote:
> > There're many truncated kthreads in the kernel, which may make trouble
> > for the user, for example, the user can't get detailed device
> > information from the task comm.
> >
> > This patchset tries to improve this problem fundamentally by extending
> > the task comm size from 16 to 24, which is a very simple way.
> >
> > In order to do that, we have to do some cleanups first.
> >
> > 1. Make the copy of task comm always safe no matter what the task
> > comm size is. For example,
> >
> > 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)
> >
> > After this step, the comm size change won't make any trouble to the
> > kernel or the in-tree tools for example perf, BPF programs.
> >
> > 2. Cleanup some old hard-coded 16
> > Actually we don't need to convert all of them to TASK_COMM_LEN or
> > TASK_COMM_LEN_16, what we really care about is if the convert can
> > make the code more reasonable or easier to understand. For
> > example, some in-tree tools read the comm from sched:sched_switch
> > tracepoint, as it is derived from the kernel, we'd better make them
> > consistent with the kernel.
>
> The above changes make sense even if we do not extend comm[] array in
> task_struct.
>
>
> > 3. Extend the task comm size from 16 to 24
> > task_struct is growing rather regularly by 8 bytes. This size change
> > should be acceptable. We used to think about extending the size for
> > CONFIG_BASE_FULL only, but that would be a burden for maintenance
> > and introduce code complexity.
> >
> > 4. Print a warning if the kthread comm is still truncated.
> >
> > 5. What will happen to the out-of-tree tools after this change?
> > If the tool get task comm through kernel API, for example prctl(2),
> > bpf_get_current_comm() and etc, then it doesn't matter how large the
> > user buffer is, because it will always get a string with a nul
> > terminator. While if it gets the task comm through direct string copy,
> > the user tool must make sure the copied string has a nul terminator
> > itself. As TASK_COMM_LEN is not exposed to userspace, there's no
> > reason that it must require a fixed-size task comm.
>
> The amount of code that has to be updated is really high. I am pretty
> sure that there are more potential buffer overflows left.
>
> You did not commented on the concerns in the thread
> https://lore.kernel.org/all/CAADnVQKm0Ljj-w5PbkAu1ugLFnZRRPt-Vk-J7AhXxDD5xVompA@mail.gmail.com/
>
I thought Steven[1] and Kees[2] have already clearly explained why we
do it like that, so I didn't give any more words on it.
[1]. https://lore.kernel.org/all/20211025170503.59830a43@gandalf.local.home/
[2]. https://lore.kernel.org/all/202110251406.56F87A3522@keescook/
> Several people suggested to use a more conservative approach.
Yes, they are Al[3] and Alexei[4].
[3]. https://lore.kernel.org/lkml/YVkmaSUxbg%2FJtBHb@zeniv-ca.linux.org.uk/
[4]. https://lore.kernel.org/all/CAADnVQKm0Ljj-w5PbkAu1ugLFnZRRPt-Vk-J7AhXxDD5xVompA@mail.gmail.com/
> I mean
> to keep comm[16] as is and add a new pointer to the full name. The buffer
> for the long name might be dynamically allocated only when needed.
>
That would add a new allocation in the fork() for the threads with a long name.
I'm not sure if it is worth it.
> The pointer might be either in task_struct or struct kthread. It might
> be used the same way as the full name stored by workqueue kthreads.
>
If we decide to do it like that, I think we'd better add it in
task_struct, then it will work for all tasks.
> The advantage of the separate pointer:
>
> + would work for names longer than 32
> + will not open security holes in code
>
Yes, those are the advantages. And the disadvantage of it is:
- new allocation in fork()
--
Thanks
Yafang
next prev parent reply other threads:[~2021-11-01 14:35 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-01 6:04 [PATCH v7 00/11] extend task comm from 16 to 24 Yafang Shao
2021-11-01 6:04 ` [PATCH v7 01/11] fs/exec: make __set_task_comm always set a nul terminated string Yafang Shao
2021-11-01 6:04 ` [PATCH v7 02/11] fs/exec: make __get_task_comm always get " Yafang Shao
2021-11-01 6:04 ` [PATCH v7 03/11] sched.h: use __must_be_array instead of BUILD_BUG_ON in get_task_comm Yafang Shao
2021-11-01 6:04 ` [PATCH v7 04/11] drivers/infiniband: make setup_ctxt always get a nul terminated task comm Yafang Shao
2021-11-01 6:04 ` [PATCH v7 05/11] fs/binfmt_elf: make prpsinfo " Yafang Shao
2021-11-01 6:04 ` [PATCH v7 06/11] samples/bpf/test_overhead_kprobe_kern: make it adopt to task comm size change Yafang Shao
2021-11-01 6:04 ` [PATCH v7 07/11] tools/bpf/bpftool/skeleton: " Yafang Shao
2021-11-01 23:47 ` Andrii Nakryiko
2021-11-01 6:04 ` [PATCH v7 08/11] tools/perf/test: make perf test " Yafang Shao
2021-11-17 14:31 ` Arnaldo Carvalho de Melo
2021-11-18 14:18 ` Yafang Shao
2021-11-01 6:04 ` [PATCH v7 09/11] tools/testing/selftests/bpf: make it " Yafang Shao
2021-11-01 23:47 ` Andrii Nakryiko
2021-11-01 6:04 ` [PATCH v7 10/11] sched.h: extend task comm from 16 to 24 Yafang Shao
2021-11-01 6:04 ` [PATCH v7 11/11] kernel/kthread: show a warning if kthread's comm is truncated Yafang Shao
2021-11-01 12:44 ` [PATCH v7 00/11] extend task comm from 16 to 24 Matthew Wilcox
2021-11-01 13:12 ` Yafang Shao
2021-11-01 14:07 ` Petr Mladek
2021-11-01 14:34 ` Yafang Shao [this message]
2021-11-01 16:02 ` Petr Mladek
2021-11-01 16:06 ` Steven Rostedt
2021-11-02 1:09 ` Yafang Shao
2021-11-02 1:18 ` Steven Rostedt
2021-11-02 1:26 ` Yafang Shao
2021-11-02 7:56 ` Petr Mladek
2021-11-02 13:48 ` Yafang Shao
2021-11-02 9:26 ` David Hildenbrand
2021-11-04 1:37 ` Michał Mirosław
2021-11-05 6:34 ` Yafang Shao
2021-11-05 23:57 ` Michał Mirosław
2021-11-06 9:12 ` Yafang Shao
2021-11-06 11:29 ` Michał Mirosław
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