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fork()/execve()/ETXTBSY: sync parent a child duing fork() to make sure child holds a reference to the executable in the host kernel using open_exec()

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bgerofi@riken.jp
2014-09-25 15:13:41 +09:00
committed by Balazs Gerofi bgerofi@riken.jp
parent ef52ba7607
commit 43e6de8124
1 changed files with 64 additions and 2 deletions
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66
executer/user/mcexec.c
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@ -114,6 +114,7 @@ struct kernel_termios {
int main_loop(int fd, int cpu, pthread_mutex_t *lock, int mcosid);
static int fd;
static char *exec_path = NULL;
static char *altroot;
static const char rlimit_stack_envname[] = "MCKERNEL_RLIMIT_STACK";
static int ischild;
@ -541,6 +542,16 @@ int load_elf_desc(char *filename, struct program_load_desc **desc_p,
filename, ret, fd);
return ret;
}
/* Drop old name if exists */
if (exec_path) {
free(exec_path);
}
exec_path = strdup(filename);
if (!exec_path) {
fprintf(stderr, "WARNING: strdup(filename) failed\n");
}
desc = load_elf(fp, &interp_path);
if (!desc) {
@ -1495,18 +1506,30 @@ int main_loop(int fd, int cpu, pthread_mutex_t *lock, int mcosid)
case __NR_fork: {
int child;
int sync_pipe_fd[2];
char sync_msg;
if (pipe(sync_pipe_fd) != 0) {
fprintf(stderr, "fork(): error creating sync pipe\n");
do_syscall_return(fd, cpu, -1, 0, 0, 0, 0);
break;
}
child = fork();
switch (child) {
/* Error */
case -1:
fprintf(stderr, "fork(): error forking child process\n");
close(sync_pipe_fd[0]);
close(sync_pipe_fd[1]);
do_syscall_return(fd, cpu, -1, 0, 0, 0, 0);
break;
/* Child process */
case 0: {
int i;
int ret = 1;
ischild = 1;
/* Reopen device fd */
@ -1515,7 +1538,10 @@ int main_loop(int fd, int cpu, pthread_mutex_t *lock, int mcosid)
if (fd < 0) {
/* TODO: tell parent something went wrong? */
fprintf(stderr, "ERROR: opening %s\n", dev);
return 1;
/* Tell parent something went wrong */
sync_msg = 1;
goto fork_child_sync_pipe;
}
/* Reinit signals and syscall threads */
@ -1525,17 +1551,53 @@ int main_loop(int fd, int cpu, pthread_mutex_t *lock, int mcosid)
__dprintf("pid(%d): signals and syscall threads OK\n",
getpid());
/* Hold executable also in the child process */
if ((ret = ioctl(fd, MCEXEC_UP_OPEN_EXEC, exec_path))
!= 0) {
fprintf(stderr, "Error: open_exec() fails for %s: %d (fd: %d)\n",
exec_path, ret, fd);
goto fork_child_sync_pipe;
}
/* Tell parent everything went OK */
sync_msg = 0;
fork_child_sync_pipe:
if (write(sync_pipe_fd[1], &sync_msg, 1) != 1) {
fprintf(stderr, "ERROR: writing sync pipe\n");
goto fork_child_out;
}
ret = 0;
fork_child_out:
close(sync_pipe_fd[0]);
close(sync_pipe_fd[1]);
/* TODO: does the forked thread run in a pthread context? */
for (i = 0; i <= ncpu; ++i) {
pthread_join(thread_data[i].thread_id, NULL);
}
return 0;
return ret;
}
/* Parent */
default:
if (read(sync_pipe_fd[0], &sync_msg, 1) != 1) {
fprintf(stderr, "fork(): error reading sync message\n");
child = -1;
goto sync_out;
}
if (sync_msg != 0) {
fprintf(stderr, "fork(): error with child process after fork\n");
child = -1;
goto sync_out;
}
sync_out:
close(sync_pipe_fd[0]);
close(sync_pipe_fd[1]);
do_syscall_return(fd, cpu, child, 0, 0, 0, 0);
break;
}