On Sat, Feb 12, 2022 at 06:32:08PM -0800, Andy Lutomirski wrote: > > > On Feb 12, 2022, at 3:24 AM, Robert Święcki <robert@xxxxxxxxxxx> wrote: > > > > sob., 12 lut 2022 o 05:28 Kees Cook <keescook@xxxxxxxxxxxx> napisał(a): > >> > >> Make siginfo available through PTRACE_GETSIGINFO after process death, > >> without needing to have already used PTRACE_ATTACH. Uses 48 more bytes > >> in task_struct, though I bet there might be somewhere else we could > >> stash a copy of it? > > > > An alternative way of accessing this info could be abusing the > > waitid() interface, with some additional, custom to Linux, flag > > > > waitid(P_ALL, 0, &si, __WCHILDSIGINFO); > > > > which would change what is put into si. > > > > But maybe ptrace() is better, because it's mostly incompatible with > > other OSes anyway on the behavior/flag level, while waitd() seems to > > be POSIX/BSD standard, even if Linux specifies some additional flags. > > > > > > I had a kind of opposite thought, which is that it would be very nice > to be able to get all the waitid() data without reaping a process or > even necessarily being its parent. Maybe these can be combined? A > new waitid() option like you’re suggesting could add siginfo (and > might need permissions). And we could have a different waitid() flag > that says “maybe not my child, don’t reap” (and also needs > permissions). > > Although the “don’t reap” thing is fundamentally racy. What a sane > process manager actually wants is an interface to read all this info > from a pidfd, which means it all needs to get stuck in struct pid. And /me briefly pops out from vacation Agreed and not just siginfo I would expect(?). We already came to that conclusion when we first introduced them. > task_struct needs a completion or wait queue so you can actually wait > for a pidfd to exit (unless someone already did this — I had patches a > while back). And this would be awesome. Currently, you can wait for a pidfd to exit via polling and you can use a pidfd to pass it to waitid(P_PIDFD, pidfd, ...). /me pops back into vacation
