overhaul system() and popen() to use vfork; fix various related bugs

[musl] / src / process / system.c

diff --git a/src/process/system.c b/src/process/system.c
index 0f1c07b..c8f2600 100644 (file)
--- a/src/process/system.c
+++ b/src/process/system.c
@@ -3,43 +3,62 @@
 #include <signal.h>
 #include <sys/wait.h>
 #include <errno.h>
+#include "pthread_impl.h"
+#include "libc.h"
+
+static void dummy_0()
+{
+}
+weak_alias(dummy_0, __acquire_ptc);
+weak_alias(dummy_0, __release_ptc);
+
+pid_t __vfork(void);
 
 int system(const char *cmd)
 {
        pid_t pid;
-       sigset_t old, new;
-       struct sigaction sa, oldint, oldquit;
-       int status;
+       sigset_t old;
+       struct sigaction sa = { .sa_handler = SIG_IGN }, oldint, oldquit;
+       int status = -1, i;
 
        if (!cmd) return 1;
 
-       sa.sa_handler = SIG_IGN;
-       sigemptyset(&sa.sa_mask);
-       sa.sa_flags = 0;
-
        sigaction(SIGINT, &sa, &oldint);
        sigaction(SIGQUIT, &sa, &oldquit);
-       sigaddset(&sa.sa_mask, SIGCHLD);
-       sigprocmask(SIG_BLOCK, &new, &old);
+       sigprocmask(SIG_BLOCK, SIGALL_SET, &old);
+
+       __acquire_ptc();
+       pid = __vfork();
+       __release_ptc();
 
-       pid = fork();
-       if (pid <= 0) {
+       if (pid > 0) {
+               sigset_t new = old;
+               sigaddset(&new, SIGCHLD);
+               sigprocmask(SIG_BLOCK, &new, 0);
+               while (waitpid(pid, &status, 0) && errno == EINTR);
+       }
+
+       if (pid) {
                sigaction(SIGINT, &oldint, NULL);
                sigaction(SIGQUIT, &oldquit, NULL);
                sigprocmask(SIG_SETMASK, &old, NULL);
-               if (pid == 0) {
-                       execl("/bin/sh", "sh", "-c", cmd, (char *)0);
-                       _exit(127);
-               }
-               return -1;
+               return status;
        }
-       while (waitpid(pid, &status, 0) == -1)
-               if (errno != EINTR) {
-                       status = -1;
-                       break;
+
+       /* Before we can unblock signals in the child, all signal
+        * handlers must be eliminated -- even implementation-internal
+        * ones. Otherwise, a signal handler could run in the child
+        * and clobber the parent's memory (due to vfork). */
+       for (i=1; i<=8*__SYSCALL_SSLEN; i++) {
+               struct sigaction sa;
+               __libc_sigaction(i, 0, &sa);
+               if (sa.sa_handler!=SIG_IGN && sa.sa_handler!=SIG_DFL) {
+                       sa.sa_handler = SIG_DFL;
+                       __libc_sigaction(i, &sa, 0);
                }
-       sigaction(SIGINT, &oldint, NULL);
-       sigaction(SIGQUIT, &oldquit, NULL);
+       }
+
        sigprocmask(SIG_SETMASK, &old, NULL);
-       return status;
+       execl("/bin/sh", "sh", "-c", cmd, (char *)0);
+       _exit(127);
 }