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From 3a45f6df7e5d37c1eb0c6e83b74093ef717942e6 Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Wed, 27 Aug 2014 21:42:20 +0200
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Subject: [PATCH] util: fix minimal race where we might miss SIGTERMs when
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forking off an agent
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Before forking, block all signals, and unblock them afterwards. This way
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the child will have them blocked, and we won't lose them.
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(cherry picked from commit 8a7c93d858c342744adf481565d8bb03b9713dcf)
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Related: #1134818
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---
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src/shared/util.c | 29 +++++++++++++++++++++++------
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1 file changed, 23 insertions(+), 6 deletions(-)
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diff --git a/src/shared/util.c b/src/shared/util.c
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index 090a204..0fcc130 100644
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--- a/src/shared/util.c
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+++ b/src/shared/util.c
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@@ -4991,9 +4991,9 @@ int fd_inc_rcvbuf(int fd, size_t n) {
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}
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int fork_agent(pid_t *pid, const int except[], unsigned n_except, const char *path, ...) {
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- pid_t parent_pid, agent_pid;
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- int fd;
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bool stdout_is_tty, stderr_is_tty;
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+ pid_t parent_pid, agent_pid;
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+ sigset_t ss, saved_ss;
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unsigned n, i;
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va_list ap;
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char **l;
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@@ -5001,16 +5001,25 @@ int fork_agent(pid_t *pid, const int except[], unsigned n_except, const char *pa
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assert(pid);
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assert(path);
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- parent_pid = getpid();
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-
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/* Spawns a temporary TTY agent, making sure it goes away when
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* we go away */
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+ parent_pid = getpid();
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+
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+ /* First we temporarily block all signals, so that the new
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+ * child has them blocked initially. This way, we can be sure
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+ * that SIGTERMs are not lost we might send to the agent. */
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+ assert_se(sigfillset(&ss) >= 0);
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+ assert_se(sigprocmask(SIG_SETMASK, &ss, &saved_ss) >= 0);
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+
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agent_pid = fork();
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- if (agent_pid < 0)
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+ if (agent_pid < 0) {
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+ assert_se(sigprocmask(SIG_SETMASK, &saved_ss, NULL) >= 0);
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return -errno;
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+ }
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if (agent_pid != 0) {
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+ assert_se(sigprocmask(SIG_SETMASK, &saved_ss, NULL) >= 0);
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*pid = agent_pid;
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return 0;
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}
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@@ -5021,8 +5030,14 @@ int fork_agent(pid_t *pid, const int except[], unsigned n_except, const char *pa
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if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0)
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_exit(EXIT_FAILURE);
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+ /* Make sure we actually can kill the agent, if we need to, in
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+ * case somebody invoked us from a shell script that trapped
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+ * SIGTERM or so... */
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+ reset_all_signal_handlers();
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+ reset_signal_mask();
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+
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/* Check whether our parent died before we were able
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- * to set the death signal */
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+ * to set the death signal and unblock the signals */
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if (getppid() != parent_pid)
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_exit(EXIT_SUCCESS);
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@@ -5033,6 +5048,8 @@ int fork_agent(pid_t *pid, const int except[], unsigned n_except, const char *pa
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stderr_is_tty = isatty(STDERR_FILENO);
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if (!stdout_is_tty || !stderr_is_tty) {
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+ int fd;
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+
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/* Detach from stdout/stderr. and reopen
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* /dev/tty for them. This is important to
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* ensure that when systemctl is started via
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