From 2f584bd93d64a75ab11b5a5aa31d0b7145da5a86 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <[email protected]>
Date: Fri, 26 Apr 2019 13:37:31 +0200
Subject: [PATCH] basic/virt: try the /proc/1/sched hack also for PID1

If a container manager does not set $container, we could end up
in a strange situation when detect-virt returns container-other when
run as non-pid-1 and none when run as pid-1.

(cherry picked from commit 342bed02084c4396dd2f1054bd559bfb2699cfcb)
Resolves: #1868877
---
 src/basic/virt.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/basic/virt.c b/src/basic/virt.c
index e05b3e6d99..dfa1525219 100644
--- a/src/basic/virt.c
+++ b/src/basic/virt.c
@@ -427,7 +427,6 @@ finish:
 }
 
 int detect_container(void) {
-
         static const struct {
                 const char *value;
                 int id;
@@ -456,9 +455,15 @@ int detect_container(void) {
         }
 
         if (getpid_cached() == 1) {
-                /* If we are PID 1 we can just check our own environment variable, and that's authoritative. */
-
+                /* If we are PID 1 we can just check our own environment variable, and that's authoritative.
+                 * We distinguish three cases:
+                 * - the variable is not defined → we jump to other checks
+                 * - the variable is defined to an empty value → we are not in a container
+                 * - anything else → some container, either one of the known ones or "container-other"
+                 */
                 e = getenv("container");
+                if (!e)
+                        goto check_sched;
                 if (isempty(e)) {
                         r = VIRTUALIZATION_NONE;
                         goto finish;
@@ -486,8 +491,9 @@ int detect_container(void) {
         if (r < 0) /* This only works if we have CAP_SYS_PTRACE, hence let's better ignore failures here */
                 log_debug_errno(r, "Failed to read $container of PID 1, ignoring: %m");
 
-        /* Interestingly /proc/1/sched actually shows the host's PID for what we see as PID 1. Hence, if the PID shown
-         * there is not 1, we know we are in a PID namespace. and hence a container. */
+        /* Interestingly /proc/1/sched actually shows the host's PID for what we see as PID 1. If the PID
+         * shown there is not 1, we know we are in a PID namespace and hence a container. */
+ check_sched:
         r = read_one_line_file("/proc/1/sched", &m);
         if (r >= 0) {
                 const char *t;