hush: fix stdin of backgrounded pipe

function                                             old     new   delta
run_list                                            2450    2502     +52

3 files changed, 35 insertions, 10 deletions

diff --git a/shell/hush.c b/shell/hush.c
index 2c2750fc8..d08652656 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -3369,7 +3369,6 @@ static int run_pipe(struct pipe *pi)
         static const char *const null_ptr = NULL;
         int i;
         int nextin;
-        int pipefds[2];         /* pipefds[0] is for reading */
         struct command *command;
         char **argv_expanded;
         char **argv;
@@ -3552,6 +3551,7 @@ static int run_pipe(struct pipe *pi)
         nextin = 0;
 
         for (i = 0; i < pi->num_cmds; i++) {
+                struct fd_pair pipefds;
 #if !BB_MMU
                 volatile nommu_save_t nommu_save;
                 nommu_save.new_env = NULL;
@@ -3568,10 +3568,10 @@ static int run_pipe(struct pipe *pi)
                 }
 
                 /* pipes are inserted between pairs of commands */
-                pipefds[0] = 0;
-                pipefds[1] = 1;
+                pipefds.rd = 0;
+                pipefds.wr = 1;
                 if ((i + 1) < pi->num_cmds)
-                        xpipe(pipefds);
+                        xpiped_pair(pipefds);
 
                 command->pid = BB_MMU ? fork() : vfork();
                 if (!command->pid) { /* child */
@@ -3592,10 +3592,18 @@ static int run_pipe(struct pipe *pi)
                                 }
                         }
 #endif
-                        xmove_fd(nextin, 0);
-                        xmove_fd(pipefds[1], 1); /* write end */
-                        if (pipefds[0] > 1)
-                                close(pipefds[0]); /* read end */
+                        if (pi->alive_cmds == 0 && pi->followup == PIPE_BG) {
+                                /* 1st cmd in backgrounded pipe
+                                 * should have its stdin /dev/null'ed */
+                                close(0);
+                                if (open(bb_dev_null, O_RDONLY))
+                                        xopen("/", O_RDONLY);
+                        } else {
+                                xmove_fd(nextin, 0);
+                        }
+                        xmove_fd(pipefds.wr, 1);
+                        if (pipefds.rd > 1)
+                                close(pipefds.rd);
                         /* Like bash, explicit redirects override pipes,
                          * and the pipe fd is available for dup'ing. */
                         if (setup_redirects(command, NULL))
@@ -3640,9 +3648,9 @@ static int run_pipe(struct pipe *pi)
                 if (i)
                         close(nextin);
                 if ((i + 1) < pi->num_cmds)
-                        close(pipefds[1]); /* write end */
+                        close(pipefds.wr);
                 /* Pass read (output) pipe end to next iteration */
-                nextin = pipefds[0];
+                nextin = pipefds.rd;
         }
 
         if (!pi->alive_cmds) {
diff --git a/shell/hush_test/hush-misc/redir5.right b/shell/hush_test/hush-misc/redir5.right
new file mode 100644
index 000000000..52cce4feb
--- /dev/null
+++ b/shell/hush_test/hush-misc/redir5.right
@@ -0,0 +1,4 @@
+Backgrounded pipes shall have their stdin redirected to /dev/null
+Zero:0
+Zero:0
+Done
diff --git a/shell/hush_test/hush-misc/redir5.tests b/shell/hush_test/hush-misc/redir5.tests
new file mode 100755
index 000000000..957f9c81f
--- /dev/null
+++ b/shell/hush_test/hush-misc/redir5.tests
@@ -0,0 +1,13 @@
+echo "Backgrounded pipes shall have their stdin redirected to /dev/null"
+
+# 1. bash does not redirect stdin to /dev/null if it is interactive.
+# hush does it always (this is allowed by standards).
+
+# 2. Failure will result in this script hanging
+
+cat & wait; echo Zero:$?
+
+# This does not work for bash! bash bug?
+cat | cat & wait; echo Zero:$?
+
+echo Done