On Tue, 5 Nov 2019, Florian Weimer wrote: > * Thomas Gleixner: > > > On Tue, 5 Nov 2019, Carlos O'Donell wrote: > >> On 11/5/19 6:56 AM, Thomas Gleixner wrote: > >> The other issue is this: > >> > >> "Robust mutexes do not take ROBUST_LIST_LIMIT into account" > >> https://sourceware.org/bugzilla/show_bug.cgi?id=19089 > > > > "The kernel limits the length of the robust mutex list to 2048 entries. > > This constant does not seem to be exported to user space." > > > > FWIW, the constant is defined in the UAPI futex header. > > > > The main concern here is not the actual number of futexes held by a task. > > > > The real issue is that the robust list could be circular by incident or > > malice and there is no way for the kernel to figure that out. That would > > prevent the task from exiting and make it iterate over the list until > > doomsday, i.e. a nice unpriviledged DoS. > > > > So I fear the kernel cannot really help with this one. > > I'm actually fine with treating ROBUST_LIST_LIMIT as an ABI constant. > It's just not clear to me if the constant has this status today. I > suspect it was just split from the implementation headers at one point. Yes, but we really can declare it as an ABI constant. I think the limit is reasonably sized. But I'm not familiar with the lock nesting expectations of insanely big enterprise applications. Thanks, tglx
