[Libguestfs] [PATCH] daemon: always provide stdin when running chroot commands (RHBZ#1280029)

[Pino Toscano]

When running commands in the mounted guest (using the "command" API, and
APIs based on it), provide the /dev/null from the appliance as open fd
for stdin.  Commands usually assume stdin is open if they didn't close
it explicitly, so this should avoid crashes or misbehavings due to that.
---
 daemon/command.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/daemon/command.c b/daemon/command.c
index 1593de9..b2d84ca 100644
--- a/daemon/command.c
+++ b/daemon/command.c
@@ -23,6 +23,8 @@
 #include <stdbool.h>
 #include <string.h>
 #include <sys/stat.h>
+#include <sys/types.h>
+#include <fcntl.h>
 
 #include "guestfs_protocol.h"
 #include "daemon.h"
@@ -242,7 +244,7 @@ do_command (char *const *argv)
 {
   char *out;
   CLEANUP_FREE char *err = NULL;
-  int r;
+  int r, fd, flags;
   CLEANUP_BIND_STATE struct bind_state bind_state = { .mounted = false };
   CLEANUP_RESOLVER_STATE struct resolver_state resolver_state =
     { .mounted = false };
@@ -259,6 +261,17 @@ do_command (char *const *argv)
     return NULL;
   }
 
+  /* Provide /dev/null as stdin for the command, since we want
+   * to make sure processes have an open stdin, and it is not
+   * possible to rely on the guest to provide it (Linux guests
+   * get /dev dynamically populated at runtime by udev).
+   */
+  fd = open ("/dev/null", O_RDONLY|O_CLOEXEC);
+  if (fd == -1) {
+    reply_with_perror ("/dev/null");
+    return NULL;
+  }
+
   if (bind_mount (&bind_state) == -1)
     return NULL;
   if (enable_network) {
@@ -266,8 +279,10 @@ do_command (char *const *argv)
       return NULL;
   }
 
+  flags = COMMAND_FLAG_CHROOT_COPY_FILE_TO_STDIN | fd;
+
   CHROOT_IN;
-  r = commandv (&out, &err, (const char * const *) argv);
+  r = commandvf (&out, &err, flags, (const char * const *) argv);
   CHROOT_OUT;
 
   free_bind_state (&bind_state);
-- 
2.1.0