Re: [PATCH] prctl: add PR_[GS]ET_KILLABLE
From: Jann Horn <jannh@google.com>
Date: 2018-07-31 16:26:32
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On Mon, Jul 30, 2018 at 10:01 AM Jürg Billeter [off-list ref] wrote:
PR_SET_KILLABLE clears the SIGNAL_UNKILLABLE flag. This allows CLONE_NEWPID tasks to restore normal signal behavior, opting out of the special signal protection for init processes. This is required for job control in a shell that uses CLONE_NEWPID for child processes. This prctl does not allow setting the SIGNAL_UNKILLABLE flag, only clearing. Signed-off-by: Jürg Billeter <redacted> ---
[...]
quoted hunk ↗ jump to hunk
diff --git a/kernel/sys.c b/kernel/sys.c index 38509dc1f77b..264de630d548 100644 --- a/kernel/sys.c +++ b/kernel/sys.c
[...]
+ case PR_SET_KILLABLE: + if (arg2 != 1 || arg3 || arg4 || arg5) + return -EINVAL; + me->signal->flags &= ~SIGNAL_UNKILLABLE; + break;
I don't have an opinion on this patchset otherwise, but should this
prctl maybe block PR_SET_KILLABLE if you're actually the real init
process? This seems like it could potentially lead to weird things.
This code in kernel/fork.c seems to rely on the fact that global init
is SIGNAL_UNKILLABLE, and probably also leads to weirdness if
container init is non-SIGNAL_UNKILLABLE:
/*
* Siblings of global init remain as zombies on exit since they are
* not reaped by their parent (swapper). To solve this and to avoid
* multi-rooted process trees, prevent global and container-inits
* from creating siblings.
*/
if ((clone_flags & CLONE_PARENT) &&
current->signal->flags & SIGNAL_UNKILLABLE)
return ERR_PTR(-EINVAL);