> 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 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.
