Log a different message when a fatal signal has been delivered before

the program issued its first syscall. This usually happens when the
program is too big to be loaded, but execve() has got too far to be
able to return to the original process image.

Also fixed a race condition which caused the execve() syscall to be
occassionally missed by the boxkeeper.

diff --git a/src/box.c b/src/box.c
index 7bff340ce85cbb993c5ebc0e7dba8d8a584f15c7..126452adbe176f9f511e38a47bef1e7f32cc1124 100644 (file)
--- a/src/box.c
+++ b/src/box.c
@@ -44,6 +44,7 @@ static int is_ptraced;
 static volatile int timer_tick;
 static struct timeval start_time;
 static int ticks_per_sec;
+static int exec_seen;
 
 #if defined(__GLIBC__) && __GLIBC__ == 2 && __GLIBC_MINOR__ > 0
 /* glibc 2.1 or newer -> has lseek64 */
@@ -161,11 +162,6 @@ valid_syscall(struct user *u)
 {
   switch (u->regs.orig_eax)
     {
-    case __NR_execve:
-      {
-       static int exec_counter;
-       return !exec_counter++;
-      }
     case __NR_open:
     case __NR_creat:
     case __NR_unlink:
@@ -408,7 +404,7 @@ boxkeeper(void)
       if (WIFSIGNALED(stat))
        {
          box_pid = 0;
-         die("Caught fatal signal %d", WTERMSIG(stat));
+         die("Caught fatal signal %d%s", WTERMSIG(stat), (syscall_count ? "" : " during startup"));
        }
       if (WIFSTOPPED(stat))
        {
@@ -425,8 +421,15 @@ boxkeeper(void)
              else if (stop_count & 1)          /* Syscall entry */
                {
                  msg(">> Syscall %3ld (%08lx,%08lx,%08lx) ", u.regs.orig_eax, u.regs.ebx, u.regs.ecx, u.regs.edx);
-                 syscall_count++;
-                 if (!valid_syscall(&u))
+                 if (!exec_seen)
+                   {
+                     msg("[master] ");
+                     if (u.regs.orig_eax == __NR_execve)
+                       exec_seen = 1;
+                   }
+                 else if (valid_syscall(&u))
+                   syscall_count++;
+                 else
                    {
                      /*
                       * Unfortunately, PTRACE_KILL kills _after_ the syscall completes,
@@ -491,8 +494,14 @@ box_inside(int argc, char **argv)
   rl.rlim_cur = rl.rlim_max = 64;
   if (setrlimit(RLIMIT_NOFILE, &rl) < 0)
     die("setrlimit: %m");
-  if (filter_syscalls && ptrace(PTRACE_TRACEME) < 0)
-    die("ptrace(PTRACE_TRACEME): %m");
+  if (filter_syscalls)
+    {
+      if (ptrace(PTRACE_TRACEME) < 0)
+       die("ptrace(PTRACE_TRACEME): %m");
+      /* Trick: Make sure that we are stopped until the boxkeeper wakes up. */
+      signal(SIGCHLD, SIG_IGN);
+      raise(SIGCHLD);
+    }
   execve(args[0], args, (pass_environ ? environ : env));
   die("execve(\"%s\"): %m", args[0]);
 }