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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id b7sm9734402pfm.28.2021.10.25.14.30.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 25 Oct 2021 14:30:36 -0700 (PDT) Date: Mon, 25 Oct 2021 14:30:36 -0700 From: Kees Cook To: Yafang Shao Cc: akpm@linux-foundation.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, arnaldo.melo@gmail.com, pmladek@suse.com, peterz@infradead.org, viro@zeniv.linux.org.uk, valentin.schneider@arm.com, qiang.zhang@windriver.com, robdclark@chromium.org, christian@brauner.io, dietmar.eggemann@arm.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, davem@davemloft.net, kuba@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, dennis.dalessandro@cornelisnetworks.com, mike.marciniszyn@cornelisnetworks.com, dledford@redhat.com, jgg@ziepe.ca, linux-rdma@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, oliver.sang@intel.com, lkp@intel.com, Andrii Nakryiko Subject: Re: [PATCH v6 11/12] sched.h: extend task comm from 16 to 24 Message-ID: <202110251429.DD44ED7B76@keescook> References: <20211025083315.4752-1-laoar.shao@gmail.com> <20211025083315.4752-12-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211025083315.4752-12-laoar.shao@gmail.com> X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 07908F000090 X-Stat-Signature: 3csucqob1wqc79hqc75gpcf9g6cxeuzw Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=Zdn6oHYx; dmarc=pass (policy=none) header.from=chromium.org; spf=pass (imf17.hostedemail.com: domain of keescook@chromium.org designates 209.85.214.182 as permitted sender) smtp.mailfrom=keescook@chromium.org X-HE-Tag: 1635197437-691956 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 > Cc: Mathieu Desnoyers > Cc: Arnaldo Carvalho de Melo > Cc: Andrii Nakryiko > Cc: Peter Zijlstra > Cc: Steven Rostedt > Cc: Al Viro > Cc: Kees Cook > Cc: Petr Mladek > --- > 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 > -- Kees Cook