@@ -1189,16 +1189,6 @@ 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
@@ -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\\");
@@ -1121,9 +1121,12 @@ 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];
@@ -1938,10 +1941,23 @@ 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.
+ *
+ * - BUILD_BUG_ON() can help prevent the buf from being truncated.
+ * Since the callers don't perform any return value checks, this safeguard is
+ * necessary.
+ */
#define get_task_comm(buf, tsk) ({ \
- BUILD_BUG_ON(sizeof(buf) != TASK_COMM_LEN); \
- __get_task_comm(buf, sizeof(buf), tsk); \
+ BUILD_BUG_ON(sizeof(buf) < TASK_COMM_LEN); \
+ strscpy_pad(buf, (tsk)->comm); \
+ buf; \
})
#ifdef CONFIG_SMP
@@ -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;
}
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 Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> 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/ Signed-off-by: Yafang Shao <laoar.shao@gmail.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Christian Brauner <brauner@kernel.org> Cc: Jan Kara <jack@suse.cz> Cc: Eric Biederman <ebiederm@xmission.com> Cc: Kees Cook <keescook@chromium.org> Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com> Cc: Matus Jokay <matus.jokay@stuba.sk> Cc: Alejandro Colomar <alx@kernel.org> Cc: "Serge E. Hallyn" <serge@hallyn.com> --- fs/exec.c | 10 ---------- fs/proc/array.c | 2 +- include/linux/sched.h | 28 ++++++++++++++++++++++------ kernel/kthread.c | 2 +- 4 files changed, 24 insertions(+), 18 deletions(-)