From 5a5c35c3a01afec515e688c8366e6f893985518d Mon Sep 17 00:00:00 2001 From: Richard Weinberger Date: Tue, 16 Apr 2013 23:42:23 +0200 Subject: [PATCH] start: Detect early failure of the new child If the process in the new namespace dies very early we have currently no chance to detect this. The parent process will just die due to SIGPIPE if it write to the fd used for synchronisation and nobody will notice the real cause of the problem. Install a SIGCHLD handler to detect the death. Later when the child does execve() to the init within the new namespace the handler will be disabled automatically. Signed-off-by: Richard Weinberger Acked-by: Serge E. Hallyn --- src/lxc/start.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/src/lxc/start.c b/src/lxc/start.c index aefccd650..a58737a4f 100644 --- a/src/lxc/start.c +++ b/src/lxc/start.c @@ -198,6 +198,7 @@ static int setup_signal_fd(sigset_t *oldmask) sigdelset(&mask, SIGILL) || sigdelset(&mask, SIGSEGV) || sigdelset(&mask, SIGBUS) || + sigdelset(&mask, SIGCHLD) || sigprocmask(SIG_BLOCK, &mask, oldmask)) { SYSERROR("failed to set signal mask"); return -1; @@ -739,10 +740,29 @@ int save_phys_nics(struct lxc_conf *conf) return 0; } +static void sigchild_handler(int sig) +{ + int status; + pid_t child; + + child = wait(&status); + if (child < 0) { + SYSERROR("SIGCHLD caught but wait() failed: %m\n"); + return; + } + + if (WIFSIGNALED(status)) + ERROR("Process in the new namespace died before execve()" + " due to signal: %i", WTERMSIG(status)); + else if (WIFEXITED(status)) + ERROR("Process in the new namespace died before execve()" + " with exit code: %i", WIFEXITED(status)); +} int lxc_spawn(struct lxc_handler *handler) { int failed_before_rename = 0; + struct sigaction act; const char *name = handler->name; if (lxc_sync_init(handler)) @@ -793,6 +813,14 @@ int lxc_spawn(struct lxc_handler *handler) goto out_delete_net; } + /* + * Install a SIGCHLD handler to detect the death of the new child between + * clone() and execve(). + */ + memset(&act, 0, sizeof(act)); + act.sa_handler = sigchild_handler; + sigaction(SIGCHLD, &act, NULL); + /* Create a process in a new set of namespaces */ handler->pid = lxc_clone(do_start, handler, handler->clone_flags); if (handler->pid < 0) { -- 2.39.5