From 625b30e09d0090f81722aa8f02e7057839dfcf4f Mon Sep 17 00:00:00 2001

From: Lennart Poettering <lennart@poettering.net>

Date: Fri, 9 Feb 2018 17:05:17 +0100

Subject: [PATCH] service: relax PID file symlink chain checks a bit (#8133)

Let's read the PID file after all if there's a potentially unsafe

symlink chain in place. But if we do, then refuse taking the PID if its

outside of the cgroup.

Fixes: #8085

(cherry picked from commit 73969ab61c39357e6892747e43307fbf07cafbed)

(cherry picked from commit ce87ed7b47c61e649a0f9da39d272631b9524740)

Resolves: #1729414

---

 src/core/service.c | 15 +++++++++++++--

 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/core/service.c b/src/core/service.c

index eaa588863f..6b61ccac18 100644

--- a/src/core/service.c

+++ b/src/core/service.c

@@ -736,6 +736,7 @@ static int service_is_suitable_main_pid(Service *s, pid_t pid, int prio) {

 static int service_load_pid_file(Service *s, bool may_warn) {

         char procfs[sizeof("/proc/self/fd/") - 1 + DECIMAL_STR_MAX(int)];

+        bool questionable_pid_file = false;

         _cleanup_free_ char *k = NULL;

         _cleanup_close_ int fd = -1;

         int r, prio;

@@ -749,8 +750,13 @@ static int service_load_pid_file(Service *s, bool may_warn) {

         prio = may_warn ? LOG_INFO : LOG_DEBUG;

         fd = chase_symlinks(s->pid_file, NULL, CHASE_OPEN|CHASE_SAFE, NULL);

-        if (fd == -EPERM)

-                return log_unit_full_errno(UNIT(s)->id, prio, fd, "Permission denied while opening PID file or unsafe symlink chain: %s", s->pid_file);

+        if (fd == -EPERM) {

+                log_unit_full(UNIT(s)->id, LOG_DEBUG, "Permission denied while opening PID file or potentially unsafe symlink chain, will now retry with relaxed checks: %s", s->pid_file);

+

+                questionable_pid_file = true;

+

+                fd = chase_symlinks(s->pid_file, NULL, CHASE_OPEN, NULL);

+        }

         if (fd < 0)

                 return log_unit_full_errno(UNIT(s)->id, prio, fd, "Can't open PID file %s (yet?) after %s: %m", s->pid_file, service_state_to_string(s->state));

@@ -773,6 +779,11 @@ static int service_load_pid_file(Service *s, bool may_warn) {

         if (r == 0) {

                 struct stat st;

+                if (questionable_pid_file) {

+                        log_unit_error(UNIT(s)->id, "Refusing to accept PID outside of service control group, acquired through unsafe symlink chain: %s", s->pid_file);

+                        return -EPERM;

+                }

+

                 /* Hmm, it's not clear if the new main PID is safe. Let's allow this if the PID file is owned by root */

                 if (fstat(fd, &st) < 0)