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Differential D58393

getpgrp(2), getsid(2): allow to call on zombies
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Authored by kib on Jul 22 2026, 9:51 AM.
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arrowd
imp
olce

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markj
kevans
kib
Summary

Also be more protective in getsid().

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rG FreeBSD src repository
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kib created this revision.Jul 22 2026, 9:51 AM
Herald added subscribers: olce, imp. · View Herald TranscriptJul 22 2026, 9:51 AM
kib requested review of this revision.Jul 22 2026, 9:51 AM
markj added a comment.Jul 22 2026, 6:14 PM

Why?

sys/kern/kern_prot.c
247–250

There is no corresponding check p->p_pgrp != NULL in sys_getpgid() above.

I suspect it's impossible to have a NULL p->p_pgrp or p->p_pgrp->pg_session.

kib added a comment.Jul 22 2026, 9:02 PM
In D58393#1339635, @markj wrote:

Why?

https://gitlab.haskell.org/ghc/ghc/-/work_items/27512#note_686988
> But the hypothesis here is that getpgid on a zombie process fails, probably ESRCH.
sys/kern/kern_prot.c
247–250

For p_pgrp yes, it is only cleared on reap.
But for the pg_session, I am not sure. What makes me wonder is the number of checks for p->p_session != NULL in the tree.

kib added a subscriber: arrowd.Jul 22 2026, 9:03 PM
markj added inline comments.Jul 22 2026, 9:09 PM
sys/kern/kern_prot.c
247–250

Yeah, it's not very clear to me either. I suspect it is always non-NULL. e.g., pgdelete() will unconditionally dereference pg_session.

252
kib marked 2 inline comments as done.Jul 22 2026, 10:01 PM
kib added inline comments.
sys/kern/kern_prot.c
247–250

I dropped the p_pgrp check, but kept pg_session. I think this should follow the existing pattern for now, and cleaned with the global sweep.

kib updated this revision to Diff 182485.Jul 22 2026, 10:01 PM
kib marked 2 inline comments as done.

Return error.

markj accepted this revision.Jul 23 2026, 1:21 PM
markj added inline comments.
sys/kern/kern_prot.c
252

Also need to initialize error to 0 for the pid == 0 case.

This revision is now accepted and ready to land.Jul 23 2026, 1:21 PM
kib updated this revision to Diff 182531.Jul 23 2026, 3:13 PM

Initialize error.

This revision now requires review to proceed.Jul 23 2026, 3:13 PM
kib mentioned this in rG8f320c2bc473: getpgrp(2), getsid(2): allow to call on zombies.Jul 23 2026, 11:51 PM
kib accepted this revision.Jul 23 2026, 11:53 PM
This revision is now accepted and ready to land.Jul 23 2026, 11:53 PM
kib closed this revision.Jul 23 2026, 11:53 PM

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kern/
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Diff 182485

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sys/kern/kern_prot.c

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