Messages in this thread | | | Date | Tue, 6 Jan 2009 23:45:58 -0800 | From | Sukadev Bhattiprolu <> | Subject | [PATCH 0/7][v6] Container-init signal semantics |
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Container-init must behave like global-init to processes within the container and hence it must be immune to unhandled fatal signals from within the container (i.e SIG_DFL signals that terminate the process).
But the same container-init must behave like a normal process to processes in ancestor namespaces and so if it receives the same fatal signal from a process in ancestor namespace, the signal must be processed.
Implementing these semantics requires that send_signal() determine pid namespace of the sender but since signals can originate from workqueues/ interrupt-handlers, determining pid namespace of sender may not always be possible or safe.
This patchset implements the design/simplified semantics suggested by Oleg Nesterov. The simplified semantics for container-init are:
- container-init must never be terminated by a signal from a descendant process.
- container-init must never be immune to SIGKILL from an ancestor namespace (so a process in parent namespace must always be able to terminate a descendant container).
- container-init may be immune to unhandled fatal signals (like SIGUSR1) even if they are from ancestor namespace (SIGKILL is the only reliable signal from ancestor namespace).
Patches in this set:
[PATCH 1/7] Remove 'handler' parameter to tracehook functions [PATCH 2/7] Protect init from unwanted signals more [PATCH 3/7] Add from_ancestor_ns parameter to send_signal() [PATCH 4/7] Define siginfo_from_ancestor_ns() [PATCH 5/7] Protect cinit from unblocked SIG_DFL signals [PATCH 6/7] Protect cinit from blocked fatal signals [PATCH 7/7] SI_USER: Masquerade si_pid when crossing pid ns boundary
Changelog[v6]:
- Patches 3,4: Have kill_pid_info_as_uid() pass in 'from_ancestor_ns' parameter to __send_signal() and remove SI_ASYNCIO check in siginfo_from_user(). - Patches 4,6: Update changelog and simplify code
Changelog[v5]: - Patch 2/6: Remove SIG_IGN check in sig_task_ignored() and let sig_handler_ignored() check SIG_IGN. - Patch 3/6. Put siginfo_from_ancestor_ns() back under CONFIG_PID_NS and remove warning in rt_sigqueueinfo(). - (Patch 5/6)Simplify check in get_signal_to_deliver() - (Patch 6/6)Simplify masquerading pid - LTP-20081219-intermediate showed no new errors on 2.6.28-rc5-mm2.
Changelog[v4]: - [Bugfix] Patch 3/7. Check ns == NULL in siginfo_from_ancestor_ns(). Although http://lkml.org/lkml/2008/12/16/502 makes it less likely that ns == NULL, looks like an explicit check won't hurt ? - Remove SIGNAL_UNKILLABLE_FROM_NS flag and simplify logic as suggested by Oleg Nesterov. - Dropped patch that set SIGNAL_UNKILLABLE_FROM_NS and set SIGNAL_UNKILLABLE in patch 5/7 to be bisect-safe. - Add a warning in rt_sigqueueinfo() if SI_ASYNCIO is used (patch 3/7) - Added two patches (6/7 and 7/7) to masquerade si_pid for SI_USER and SI_TKILL
Changelog[v3]: Changes based on discussions of previous version: http://lkml.org/lkml/2008/11/25/458
Major changes:
- Define SIGNAL_UNKILLABLE_FROM_NS and use in container-inits to skip fatal signals from same namespace but process SIGKILL/SIGSTOP from ancestor namespace. - Use SI_FROMUSER() and si_code != SI_ASYNCIO to determine if it is safe to dereference pid-namespace of caller. Highly experimental :-) - Masquerading si_pid when crossing namespace boundary: relevant patches merged in -mm and dropped from this set.
Minor changes:
- Remove 'handler' parameter to tracehook functions - Update sig_ignored() to drop SIG_DFL signals to global init early (tried to address Roland's and Oleg's comments) - Use 'same_ns' flag to drop SIGKILL/SIGSTOP to cinit from same namespace
TODO: - Add a check in fs/proc/array.c:task_sig() to include SIG_DFL signals from same namespace in 'ignored signals' set for container/global init.
Limitations/side-effects of current design
- Container-init is immune to suicide - kill(getpid(), SIGKILL) is ignored. Use exit() :-)
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