The patch titled
signals: protect cinit from blocked fatal signals
has been added to the -mm tree. Its filename is
signals-protect-cinit-from-blocked-fatal-signals.patch
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------------------------------------------------------
Subject: signals: protect cinit from blocked fatal signals
From: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
Normally SIG_DFL signals to global and container-init are dropped early.
But if a signal is blocked when it is posted, we cannot drop the signal
since the receiver may install a handler before unblocking the signal.
Once this signal is queued however, the receiver container-init has no way
of knowing if the signal was sent from an ancestor or descendant
namespace. This patch ensures that contianer-init drops all SIG_DFL
signals in get_signal_to_deliver() except SIGKILL/SIGSTOP.
If SIGSTOP/SIGKILL originate from a descendant of container-init they are
never queued (i.e dropped in sig_ignored() in an earler patch).
If SIGSTOP/SIGKILL originate from parent namespace, the signal is queued
and container-init processes the signal.
IOW, if get_signal_to_deliver() sees a sig_kernel_only() signal for global
or container-init, the signal must have been generated internally or must
have come from an ancestor ns and we process the signal.
Further, the signal_group_exit() check was needed to cover the case of a
multi-threaded init sending SIGKILL to other threads when doing an exit()
or exec(). But since the new sig_kernel_only() check covers the SIGKILL,
the signal_group_exit() check is no longer needed and can be removed.
Finally, now that we have all pieces in place, set SIGNAL_UNKILLABLE for
container-inits.
Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Daniel Lezcano <daniel.lezcano@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/fork.c | 2 ++
kernel/signal.c | 9 ++++++++-
2 files changed, 10 insertions(+), 1 deletion(-)
diff -puN kernel/fork.c~signals-protect-cinit-from-blocked-fatal-signals kernel/fork.c
--- a/kernel/fork.c~signals-protect-cinit-from-blocked-fatal-signals
+++ a/kernel/fork.c
@@ -844,6 +844,8 @@ static int copy_signal(unsigned long clo
atomic_set(&sig->live, 1);
init_waitqueue_head(&sig->wait_chldexit);
sig->flags = 0;
+ if (clone_flags & CLONE_NEWPID)
+ sig->flags |= SIGNAL_UNKILLABLE;
sig->group_exit_code = 0;
sig->group_exit_task = NULL;
sig->group_stop_count = 0;
diff -puN kernel/signal.c~signals-protect-cinit-from-blocked-fatal-signals kernel/signal.c
--- a/kernel/signal.c~signals-protect-cinit-from-blocked-fatal-signals
+++ a/kernel/signal.c
@@ -1862,9 +1862,16 @@ relock:
/*
* Global init gets no signals it doesn't want.
+ * Container-init gets no signals it doesn't want from same
+ * container.
+ *
+ * Note that if global/container-init sees a sig_kernel_only()
+ * signal here, the signal must have been generated internally
+ * or must have come from an ancestor namespace. In either
+ * case, the signal cannot be dropped.
*/
if (unlikely(signal->flags & SIGNAL_UNKILLABLE) &&
- !signal_group_exit(signal))
+ !sig_kernel_only(signr))
continue;
if (sig_kernel_stop(signr)) {
_
Patches currently in -mm which might be from sukadev@xxxxxxxxxxxxxxxxxx are
vfs-simple_set_mnt-should-return-void.patch
devpts-must-release-s_umount-on-error.patch
signals-remove-handler-parameter-to-tracehook-functions.patch
signals-protect-init-from-unwanted-signals-more.patch
signals-add-from_ancestor_ns-parameter-to-send_signal.patch
signals-protect-cinit-from-unblocked-sig_dfl-signals.patch
signals-zap_pid_ns_process-should-use-force_sig.patch
signals-protect-cinit-from-blocked-fatal-signals.patch
signals-si_user-masquerade-si_pid-when-crossing-pid-ns-boundary.patch
pids-document-task_pgrp-task_session-is-not-safe-without-tasklist-rcu.patch
pids-document-task_pgrp-task_session-is-not-safe-without-tasklist-rcu-fix.patch
pids-improve-get_task_pid-to-fix-the-unsafe-sys_wait4-task_pgrp.patch
pids-refactor-vnr-nr_ns-helpers-to-make-them-safe.patch
pids-kill-now-unused-signal_struct-__pgrp-__session-and-friends.patch
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