[CRIU] [PATCH] restorer: block signals before restoring SIGCHLD handler

[Andrey Vagin]

Otherwise the process can handler this signal before calling sigreturn.

And threads must block signals before switching on
CR_STATE_RESTORE_SIGCHLD, because signals are restoring on this stage.

So if a thread leader starts restoring shared signals before another
thread has blocked signals, this thread can start to hadle the signal.
I have seen this race in static/sigpending.

Signed-off-by: Andrey Vagin <avagin at openvz.org>
---
 pie/restorer.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/pie/restorer.c b/pie/restorer.c
index 95bb63f..cc58584 100644
--- a/pie/restorer.c
+++ b/pie/restorer.c
@@ -211,14 +211,6 @@ static void restore_rlims(struct task_restore_core_args *ta)
 static int restore_signals(siginfo_t *ptr, int nr, bool group)
 {
 	int ret, i;
-	k_rtsigset_t to_block;
-
-	ksigfillset(&to_block);
-	ret = sys_sigprocmask(SIG_SETMASK, &to_block, NULL, sizeof(k_rtsigset_t));
-	if (ret) {
-		pr_err("Unable to block signals %d", ret);
-		return -1;
-	}
 
 	for (i = 0; i < nr; i++) {
 		siginfo_t *info = ptr + i;
@@ -272,6 +264,7 @@ static int restore_thread_common(struct rt_sigframe *sigframe,
 long __export_restore_thread(struct thread_restore_args *args)
 {
 	struct rt_sigframe *rt_sigframe;
+	k_rtsigset_t to_block;
 	unsigned long new_sp;
 	int my_pid = sys_gettid();
 	int ret;
@@ -281,6 +274,14 @@ long __export_restore_thread(struct thread_restore_args *args)
 		goto core_restore_end;
 	}
 
+	/* All signals must be handled by thread leader */
+	ksigfillset(&to_block);
+	ret = sys_sigprocmask(SIG_SETMASK, &to_block, NULL, sizeof(k_rtsigset_t));
+	if (ret) {
+		pr_err("Unable to block signals %d", ret);
+		goto core_restore_end;
+	}
+
 	rt_sigframe = (void *)args->mem_zone.rt_sigframe;
 
 	if (restore_thread_common(rt_sigframe, args))
@@ -568,6 +569,7 @@ long __export_restore_task(struct task_restore_core_args *args)
 
 	struct rt_sigframe *rt_sigframe;
 	unsigned long new_sp;
+	k_rtsigset_t to_block;
 	pid_t my_pid = sys_getpid();
 	rt_sigaction_t act;
 
@@ -853,6 +855,13 @@ long __export_restore_task(struct task_restore_core_args *args)
 
 	futex_wait_while_gt(&zombies_inprogress, 0);
 
+	ksigfillset(&to_block);
+	ret = sys_sigprocmask(SIG_SETMASK, &to_block, NULL, sizeof(k_rtsigset_t));
+	if (ret) {
+		pr_err("Unable to block signals %ld", ret);
+		goto core_restore_end;
+	}
+
 	sys_sigaction(SIGCHLD, &args->sigchld_act, NULL, sizeof(k_rtsigset_t));
 
 	ret = restore_signals(args->siginfo, args->siginfo_nr, true);
-- 
1.8.3.1