On Tue, Jan 14, 2014 at 2:13 PM, Oleg Nesterov <o...@redhat.com> wrote: > On 01/14, Oleg Nesterov wrote: >> >> On 01/14, Oleg Nesterov wrote: >> > >> > > + get_seccomp_filter(caller); >> > > + /* >> > > + * Drop the task reference to the shared ancestor since >> > > + * current's path will hold a reference. (This also >> > > + * allows a put before the assignment.) >> > > + */ >> > > + put_seccomp_filter(thread); >> > > + thread->seccomp.filter = caller->seccomp.filter; >> > >> > As I said, I do not understand this patch yet, but this looks suspicious. >> > >> > Why we can't race with this thread doing clone(CLONE_THREAD) ? We do >> > not the the new thread yet, but its ->seccomp can be already copied >> > by copy_process(), no?
Ah - I thought the tasklist_lock would catch that, but of course that happens before the tasklist_lock is needed. >> >> And it seems that this can obviously race with seccomp_attach_filter() >> called by this "thread". And... I was hoping the task_lock would cover any attach cases, but missing the copy_process() is a problem. > > Heh. I just noticed that this patch is not first in series, and I wasn't > cc'ed. I found this one on marc.info, Sorry! I shouldn't have relied on cc-cmd, I usually mess it up. > > http://marc.info/?l=linux-kernel&m=138964557211277 > > this explains task_lock(). But this can't fix the race with copy_process, > and the patch itself doesn't look right... if nothing else, we can't do > copy_from_user() under task_lock(). Thanks -- I'll take a more critical look! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
