ash: prevent ctrl-c from killing background processes

spawn_forkshell() was missing some code that would normally have
been run from forkchild when a background process was started:

- the ctrl-c handler wasn't disabled;
- standard input wasn't connected to /dev/null.

Using ctrl-c to kill a foreground process also killed background
processes.

Fixing this requires passing the forkshell mode and the number of
processes associated with the forkshell job to the child process.

1 files changed, 14 insertions, 0 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 188ec0979..0b41e7931 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -355,6 +355,10 @@ struct forkshell {
         /* type of forkshell */
         int fpid;
 
+        /* generic data, used by forkshell_child */
+        int mode;
+        int nprocs;
+
         /* optional data, used by forkshell_child */
         int flags;
         int fd[3];
@@ -15100,6 +15104,8 @@ spawn_forkshell(struct job *jp, struct forkshell *fs, int mode)
         intptr_t ret;
 
         new = forkshell_prepare(fs);
+        new->mode = mode;
+        new->nprocs = jp == NULL ? 0 : jp->nprocs;
         sprintf(buf, "%p", new->hMapFile);
         argv[2] = buf;
         ret = mingw_spawn_proc(argv);
@@ -15725,6 +15731,14 @@ forkshell_init(const char *idstr)
         reinitvar();
 
         shlvl++;
+        if (fs->mode == FORK_BG) {
+                SetConsoleCtrlHandler(NULL, TRUE);
+                if (fs->nprocs == 0) {
+                        close(0);
+                        if (open(bb_dev_null, O_RDONLY) != 0)
+                                ash_msg_and_raise_perror("can't open '%s'", bb_dev_null);
+                }
+        }
         forkshell_child(fs);
 }