On Fri, May 24, 2024 at 10:58 PM Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Fri, 24 May 2024 at 00:43, Yafang Shao <laoar.shao@xxxxxxxxx> wrote: > > > > Actually, there are already helpers for this: get_task_comm() and > > __get_task_comm(). We can simply replace the memcpy() with one of > > these > > No. We should get rid of those horrendous helpers. > > > If the task_lock() in __get_task_comm() is a concern, we could > > consider adding a new __get_current_comm(). > > The task_lock is indeed the problem - it generates locking problems > and basically means that most places cannot use them. Certainly not > things like tracing etc. > > The locking is also entirely pointless\, since absolutely nobody > cares. If somebody is changing the name at the same time - which > doesn't happen in practice - getting some halfway result is fine as > long as you get a proper NUL terminated result. > > Even for non-current, they are largely useless. They were a mistake. > > So those functions should never be used for any normal thing. Instead > of locking, the function should literally just do a "copy a couple of > words and make sure the end result still has a NUL at the end". > > That's literally what selinuxfs.c wants, for example - it copies the > thing to a local buffer not because it cares about some locking issue, > but because it wants one stable value. But by using 'memcpy()' and > that fixed size, it means that we can't sanely extend the source size > because now it wouldn't be NUL-terminated. But selinux never wanted a > lock, and never wanted any kind of *consistent* result, it just wanted > a *stable* result. > > 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) Thanks for your explanation. Let's proceed by removing the task_lock() inside __get_task_comm(). -- Regards Yafang
