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@xxxxxxxxxxxxxxxxxxxx> Link: https://lore.kernel.org/all/CAHk-=wivfrF0_zvf+oj6==Sh=-npJooP8chLPEfaFV0oNYTTBA@xxxxxxxxxxxxxx [0] Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Christian Brauner <brauner@xxxxxxxxxx> Cc: Jan Kara <jack@xxxxxxx> Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> --- fs/exec.c | 7 +++++-- include/linux/sched.h | 2 +- 2 files changed, 6 insertions(+), 3 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index b3c40fbb325f..b43992d35a8a 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1227,12 +1227,15 @@ static int unshare_sighand(struct task_struct *me) return 0; } +/* + * 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. + */ 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); diff --git a/include/linux/sched.h b/include/linux/sched.h index c75fd46506df..56a927393a38 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1083,7 +1083,7 @@ struct task_struct { * * - normally initialized setup_new_exec() * - access it with [gs]et_task_comm() - * - lock it with task_lock() + * - lock it with task_lock() for writing */ char comm[TASK_COMM_LEN]; -- 2.39.1
