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From f0fdbdb003cb3e8d8188c1c01701b510505b5b8b 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 | 35 +++++++++++++++++++++++------------
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 1 file changed, 23 insertions(+), 12 deletions(-)
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diff --git a/src/shared/util.c b/src/shared/util.c
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index e4448ff..9f25b15 100644
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--- a/src/shared/util.c
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+++ b/src/shared/util.c
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@@ -5002,9 +5002,9 @@ 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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@@ -5012,16 +5012,25 @@ 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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@@ -5032,24 +5041,26 @@ 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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         /* Don't leak fds to the agent */
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         close_all_fds(except, n_except);
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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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         stdout_is_tty = isatty(STDOUT_FILENO);
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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