From 912314fc9b63e8cffaf3d5160f9171fc6a0805d4 Mon Sep 17 00:00:00 2001
From: Christian Brauner <christian.brauner@ubuntu.com>
Date: Fri, 22 Dec 2017 22:17:44 +0100
Subject: [PATCH 1/2] start: fix death signal

On set{g,u}id() the kernel does:

 	/* dumpability changes */
	if (!uid_eq(old->euid, new->euid) ||
	    !gid_eq(old->egid, new->egid) ||
	    !uid_eq(old->fsuid, new->fsuid) ||
	    !gid_eq(old->fsgid, new->fsgid) ||
	    !cred_cap_issubset(old, new)) {
		if (task->mm)
			set_dumpable(task->mm, suid_dumpable);
		task->pdeath_signal = 0;
		smp_wmb();
	}

which means we need to re-enable the deat signal after the set{g,u}id().

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 src/lxc/start.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/lxc/start.c b/src/lxc/start.c
index c7d87fb3c..2b09d89ab 100644
--- a/src/lxc/start.c
+++ b/src/lxc/start.c
@@ -888,8 +888,9 @@ static int do_start(void *data)
 	 * exit before we set the pdeath signal leading to a unsupervized
 	 * container.
 	 */
-	if (prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0)) {
-		SYSERROR("Failed to set PR_SET_PDEATHSIG to SIGKILL.");
+	ret = prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
+	if (ret < 0) {
+		SYSERROR("Failed to set PR_SET_PDEATHSIG to SIGKILL");
 		return -1;
 	}
 
@@ -946,6 +947,13 @@ static int do_start(void *data)
 			if (ret < 0)
 				goto out_warn_father;
 		}
+
+		/* set{g,u}id() clears deathsignal */
+		ret = prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
+		if (ret < 0) {
+			SYSERROR("Failed to set PR_SET_PDEATHSIG to SIGKILL");
+			goto out_warn_father;
+		}
 	}
 
 	if (access(handler->lxcpath, X_OK)) {

From 18225d1985247a8df08d25d07b0797525847d502 Mon Sep 17 00:00:00 2001
From: Christian Brauner <christian.brauner@ubuntu.com>
Date: Fri, 22 Dec 2017 22:52:42 +0100
Subject: [PATCH 2/2] start: handle setting death signal smarter

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 src/lxc/start.c | 49 ++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 38 insertions(+), 11 deletions(-)

diff --git a/src/lxc/start.c b/src/lxc/start.c
index 2b09d89ab..d70764fa1 100644
--- a/src/lxc/start.c
+++ b/src/lxc/start.c
@@ -866,6 +866,32 @@ void lxc_abort(const char *name, struct lxc_handler *handler)
 	}
 }
 
+static int lxc_set_death_signal(int signal)
+{
+	int ret;
+	pid_t ppid;
+
+	ret = prctl(PR_SET_PDEATHSIG, signal, 0, 0, 0);
+
+	/* Check whether we have been orphaned. */
+	ppid = (pid_t)syscall(SYS_getppid);
+	if (ppid == 1) {
+		pid_t self;
+
+		self = lxc_raw_getpid();
+		ret = kill(self, SIGKILL);
+		if (ret < 0)
+			return -1;
+	}
+
+	if (ret < 0) {
+		SYSERROR("Failed to set PR_SET_PDEATHSIG to %d", signal);
+		return -1;
+	}
+
+	return 0;
+}
+
 static int do_start(void *data)
 {
 	int ret;
@@ -877,10 +903,7 @@ static int do_start(void *data)
 	gid_t new_gid;
 	int devnull_fd = -1;
 
-	if (sigprocmask(SIG_SETMASK, &handler->oldmask, NULL)) {
-		SYSERROR("Failed to set signal mask.");
-		return -1;
-	}
+	lxc_sync_fini_parent(handler);
 
 	/* This prctl must be before the synchro, so if the parent dies before
 	 * we set the parent death signal, we will detect its death with the
@@ -888,20 +911,25 @@ static int do_start(void *data)
 	 * exit before we set the pdeath signal leading to a unsupervized
 	 * container.
 	 */
-	ret = prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
+	ret = lxc_set_death_signal(SIGKILL);
 	if (ret < 0) {
 		SYSERROR("Failed to set PR_SET_PDEATHSIG to SIGKILL");
-		return -1;
+		goto out_warn_father;
 	}
 
-	lxc_sync_fini_parent(handler);
+	ret = sigprocmask(SIG_SETMASK, &handler->oldmask, NULL);
+	if (ret < 0) {
+		SYSERROR("Failed to set signal mask");
+		goto out_warn_father;
+	}
 
 	/* Don't leak the pinfd to the container. */
 	if (handler->pinfd >= 0)
 		close(handler->pinfd);
 
-	if (lxc_sync_wait_parent(handler, LXC_SYNC_STARTUP))
-		return -1;
+	ret = lxc_sync_wait_parent(handler, LXC_SYNC_STARTUP);
+	if (ret < 0)
+		goto out_warn_father;
 
 	/* Unshare CLONE_NEWNET after CLONE_NEWUSER. See
 	 * https://github.com/lxc/lxd/issues/1978.
@@ -949,7 +977,7 @@ static int do_start(void *data)
 		}
 
 		/* set{g,u}id() clears deathsignal */
-		ret = prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
+		ret = lxc_set_death_signal(SIGKILL);
 		if (ret < 0) {
 			SYSERROR("Failed to set PR_SET_PDEATHSIG to SIGKILL");
 			goto out_warn_father;
@@ -1425,7 +1453,6 @@ static int lxc_spawn(struct lxc_handler *handler)
 		SYSERROR(LXC_CLONE_ERROR);
 		goto out_delete_net;
 	}
-
 	TRACE("Cloned child process %d", handler->pid);
 
 	for (i = 0; i < LXC_NS_MAX; i++)