console: exit mainloop on SIGTERM

This allows cleanly exiting a console session without control sequences.

Relates to https://github.com/lxc/lxd/pull/4001 .

Note that the existence of a signal handler now doesn't guarantee that ts->node
is allocated. Instead, ts->node will now only be added to if stdinfd is a tty.
New checks need to take that into account.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/src/lxc/console.c b/src/lxc/console.c
index 76bf08be5c2f567cd4e974ac1c0b02ad6a740a7e..1beafa4923c680b97c8f194e9f12958f264db187 100644 (file)
--- a/src/lxc/console.c
+++ b/src/lxc/console.c
@@ -108,21 +108,30 @@ void lxc_console_sigwinch(int sig)
 int lxc_console_cb_signal_fd(int fd, uint32_t events, void *cbdata,
                               struct lxc_epoll_descr *descr)
 {
+       ssize_t ret;
        struct signalfd_siginfo siginfo;
        struct lxc_tty_state *ts = cbdata;
 
-       ssize_t ret = read(fd, &siginfo, sizeof(siginfo));
+       ret = read(fd, &siginfo, sizeof(siginfo));
        if (ret < 0 || (size_t)ret < sizeof(siginfo)) {
                ERROR("Failed to read signal info");
                return -1;
        }
 
-       lxc_console_winch(ts);
+       if (siginfo.ssi_signo == SIGTERM) {
+               DEBUG("Received SIGTERM. Detaching from the console");
+               return 1;
+       }
+
+       if (siginfo.ssi_signo == SIGWINCH)
+               lxc_console_winch(ts);
+
        return 0;
 }
 
 struct lxc_tty_state *lxc_console_signal_init(int srcfd, int dstfd)
 {
+       int ret;
        bool istty;
        sigset_t mask;
        struct lxc_tty_state *ts;
@@ -136,35 +145,45 @@ struct lxc_tty_state *lxc_console_signal_init(int srcfd, int dstfd)
        ts->masterfd = dstfd;
        ts->sigfd = -1;
 
+       sigemptyset(&mask);
+
        istty = isatty(srcfd) == 1;
        if (!istty) {
                INFO("fd %d does not refer to a tty device", srcfd);
-               return ts;
+       } else {
+               /* Add tty to list to be scanned at SIGWINCH time. */
+               lxc_list_add_elem(&ts->node, ts);
+               lxc_list_add_tail(&lxc_ttys, &ts->node);
+               sigaddset(&mask, SIGWINCH);
        }
 
-       /* add tty to list to be scanned at SIGWINCH time */
-       lxc_list_add_elem(&ts->node, ts);
-       lxc_list_add_tail(&lxc_ttys, &ts->node);
+       /* Exit the mainloop cleanly on SIGTERM. */
+       sigaddset(&mask, SIGTERM);
 
-       sigemptyset(&mask);
-       sigaddset(&mask, SIGWINCH);
-       if (sigprocmask(SIG_BLOCK, &mask, &ts->oldmask)) {
-               SYSERROR("Failed to block SIGWINCH signal");
-               ts->sigfd = -1;
-               lxc_list_del(&ts->node);
-               return ts;
+       ret = sigprocmask(SIG_BLOCK, &mask, &ts->oldmask);
+       if (ret < 0) {
+               WARN("Failed to block signals");
+               goto on_error;
        }
 
        ts->sigfd = signalfd(-1, &mask, 0);
        if (ts->sigfd < 0) {
-               SYSERROR("Failed to create signal fd");
+               WARN("Failed to create signal fd");
                sigprocmask(SIG_SETMASK, &ts->oldmask, NULL);
-               ts->sigfd = -1;
-               lxc_list_del(&ts->node);
-               return ts;
+               goto on_error;
        }
 
-       DEBUG("Process %d created signal fd %d", getpid(), ts->sigfd);
+       DEBUG("Created signal fd %d", ts->sigfd);
+       return ts;
+
+on_error:
+       ERROR("Failed to create signal fd");
+       if (ts->sigfd >= 0) {
+               close(ts->sigfd);
+               ts->sigfd = -1;
+       }
+       if (istty)
+               lxc_list_del(&ts->node);
        return ts;
 }
 
@@ -172,10 +191,14 @@ void lxc_console_signal_fini(struct lxc_tty_state *ts)
 {
        if (ts->sigfd >= 0) {
                close(ts->sigfd);
-               lxc_list_del(&ts->node);
-               sigprocmask(SIG_SETMASK, &ts->oldmask, NULL);
+
+               if (sigprocmask(SIG_SETMASK, &ts->oldmask, NULL) < 0)
+                       WARN("%s - Failed to restore signal mask", strerror(errno));
        }
 
+       if (isatty(ts->stdinfd))
+               lxc_list_del(&ts->node);
+
        free(ts);
 }