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Hallyn" Subject: [PATCH v8 1/8] Get rid of __get_task_comm() Date: Wed, 28 Aug 2024 11:03:14 +0800 Message-Id: <20240828030321.20688-2-laoar.shao@gmail.com> X-Mailer: git-send-email 2.30.1 (Apple Git-130) In-Reply-To: <20240828030321.20688-1-laoar.shao@gmail.com> References: <20240828030321.20688-1-laoar.shao@gmail.com> MIME-Version: 1.0 X-Stat-Signature: 1jyr4h95k6fbce4fd9xhofh5g6gmwoyq X-Rspam-User: X-Rspamd-Queue-Id: 466E9A0012 X-Rspamd-Server: rspam02 X-HE-Tag: 1724814226-343525 X-HE-Meta: U2FsdGVkX1+zVs8YZoSJf5YmJu4DjBgAHSFT3Wqr3KEmMAcSAM3441rnZd57p6y6UurZu8AGtZtQpHWXZAMjBJZ9tA3Tuj2PpdEy1mfcCeXc4BkgH5fwLzSWFUmMKuXnUvxR/wcuOVLEphcTb28rzsIcX4k18aSbT4K5MLILABkI9JPI0anb/JvWTLKuuUCD4nmdy0sX3rq1E08ObKlQ152Q2CFcoqA3agTcLGKYoETty82MqmECC1YHnp74EvAS5kgbzM4MHpUZG5JZ4KTrXfjR9HSWsv+vWNGq4epJr5t3IH5TEP4bclkcHpBDtDFdgplONG9Wq/+DYiiMzeaXRQ85s4uFMnrGFKtp0tbDyEvD2a/kF6QyLi1CXUbGMyHWMRYVD2wXIp44zL1InTJmvK/Qr89SW89ziIkpuxfrbpEDAf/+TSWZYAWEgoS4CfiJNrKuPLE1P7KAe73eDd6wx1qsaq7Y9gOwimoXbcSXo5sBihNBEWJh++JVsQRer4jyvQhjxXBAg0R2bXaVi0GTXMQeUDJes0pOyLDuRTFt292Op7AF110lVSe3qisFERQo1W4ctymyDA3HxwKhROHKBAPv8HdyHm+dwueRXuKmMsL+qdcf4nQ3x1Z1xsuK/FTigkD+w5+2gf2+RxGYAKsj0JvCi3HAbJ52x3E+AV9Zaoxcn6K5U0FtgQiUUvKVj9wPDpM/Wf4F04HJdDVIvHRrzet+rolV9IDgINshixi1ZVZjB2CcNiX8IOa/r21boKknmxnvMWoPhNE2GpIju2mHAcYzyaiQ7hFPEVu7noQ1BJjCH/2ZcJ54gO5rT4kFvb0StkQt8xyqqFJC8lD/T+gb3a1uFTI9avTIAJwbCwlMCvBuatIMHnDDoXoPOyM9bzU6XJ1fToQj9YUcqju4IMawmSJr4XuSbvx1jI1m8oSlvpC4PR2eK4Rt1qJjGm/flQQiGcaPMQ3gIZlvvMuNNGI 7bDdBk+z 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 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: List-Subscribe: List-Unsubscribe: We want to eliminate the use of __get_task_comm() for the following reasons: - The task_lock() is unnecessary Quoted from Linus [0]: : Since user space can randomly change their names anyway, using locking : was always wrong for readers (for writers it probably does make sense : to have some lock - although practically speaking nobody cares there : either, but at least for a writer some kind of race could have : long-term mixed results - The BUILD_BUG_ON() doesn't add any value The only requirement is to ensure that the destination buffer is a valid array. - Zeroing is not necessary in current use cases To avoid confusion, we should remove it. Moreover, not zeroing could potentially make it easier to uncover bugs. If the caller needs a zero-padded task name, it should be explicitly handled at the call site. Suggested-by: Linus Torvalds Link: https://lore.kernel.org/all/CAHk-=wivfrF0_zvf+oj6==Sh=-npJooP8chLPEfaFV0oNYTTBA@mail.gmail.com [0] Link: https://lore.kernel.org/all/CAHk-=whWtUC-AjmGJveAETKOMeMFSTwKwu99v7+b6AyHMmaDFA@mail.gmail.com/ Suggested-by: Alejandro Colomar Link: https://lore.kernel.org/all/2jxak5v6dfxlpbxhpm3ey7oup4g2lnr3ueurfbosf5wdo65dk4@srb3hsk72zwq Signed-off-by: Yafang Shao Cc: Alexander Viro Cc: Christian Brauner Cc: Jan Kara Cc: Eric Biederman Cc: Kees Cook Cc: Alexei Starovoitov Cc: Matus Jokay Cc: Alejandro Colomar Cc: "Serge E. Hallyn" --- fs/exec.c | 10 ---------- fs/proc/array.c | 2 +- include/linux/sched.h | 32 ++++++++++++++++++++++++++------ kernel/kthread.c | 2 +- 4 files changed, 28 insertions(+), 18 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 50e76cc633c4..8a23171bc3c3 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1264,16 +1264,6 @@ static int unshare_sighand(struct task_struct *me) return 0; } -char *__get_task_comm(char *buf, size_t buf_size, struct task_struct *tsk) -{ - task_lock(tsk); - /* Always NUL terminated and zero-padded */ - strscpy_pad(buf, tsk->comm, buf_size); - task_unlock(tsk); - return buf; -} -EXPORT_SYMBOL_GPL(__get_task_comm); - /* * These functions flushes out all traces of the currently running executable * so that a new one can be started diff --git a/fs/proc/array.c b/fs/proc/array.c index 34a47fb0c57f..55ed3510d2bb 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -109,7 +109,7 @@ void proc_task_name(struct seq_file *m, struct task_struct *p, bool escape) else if (p->flags & PF_KTHREAD) get_kthread_comm(tcomm, sizeof(tcomm), p); else - __get_task_comm(tcomm, sizeof(tcomm), p); + get_task_comm(tcomm, p); if (escape) seq_escape_str(m, tcomm, ESCAPE_SPACE | ESCAPE_SPECIAL, "\n\\"); diff --git a/include/linux/sched.h b/include/linux/sched.h index f8d150343d42..c40b95a79d80 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1096,9 +1096,12 @@ struct task_struct { /* * executable name, excluding path. * - * - normally initialized setup_new_exec() - * - access it with [gs]et_task_comm() - * - lock it with task_lock() + * - normally initialized begin_new_exec() + * - set it with set_task_comm() + * - strscpy_pad() to ensure it is always NUL-terminated and + * zero-padded + * - task_lock() to ensure the operation is atomic and the name is + * fully updated. */ char comm[TASK_COMM_LEN]; @@ -1914,10 +1917,27 @@ static inline void set_task_comm(struct task_struct *tsk, const char *from) __set_task_comm(tsk, from, false); } -extern char *__get_task_comm(char *to, size_t len, struct task_struct *tsk); +/* + * - Why not use task_lock()? + * User space can randomly change their names anyway, so locking for readers + * doesn't make sense. For writers, locking is probably necessary, as a race + * condition could lead to long-term mixed results. + * The strscpy_pad() in __set_task_comm() can ensure that the task comm is + * always NUL-terminated and zero-padded. Therefore the race condition between + * reader and writer is not an issue. + * + * - Why not use strscpy_pad()? + * While strscpy_pad() prevents writing garbage past the NUL terminator, which + * is useful when using the task name as a key in a hash map, most use cases + * don't require this. Zero-padding might confuse users if it’s unnecessary, + * and not zeroing might even make it easier to expose bugs. If you need a + * zero-padded task name, please handle that explicitly at the call site. + * + * - ARRAY_SIZE() can help ensure that @buf is indeed an array. + */ #define get_task_comm(buf, tsk) ({ \ - BUILD_BUG_ON(sizeof(buf) != TASK_COMM_LEN); \ - __get_task_comm(buf, sizeof(buf), tsk); \ + strscpy(buf, (tsk)->comm, ARRAY_SIZE(buf)); \ + buf; \ }) #ifdef CONFIG_SMP diff --git a/kernel/kthread.c b/kernel/kthread.c index f7be976ff88a..7d001d033cf9 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -101,7 +101,7 @@ void get_kthread_comm(char *buf, size_t buf_size, struct task_struct *tsk) struct kthread *kthread = to_kthread(tsk); if (!kthread || !kthread->full_name) { - __get_task_comm(buf, buf_size, tsk); + strscpy(buf, tsk->comm, buf_size); return; }