[PATCH] uml: close TUN/TAP file descriptors

When UML opens a TUN/TAP device, the file descriptor could be copied into
later, long-lived threads, holding the device open even after the interface is
taken down, preventing it from being brought up again.  This patch makes these
descriptors close-on-exec so that they disappear from helper processes, and
adds CLONE_FILES to a UML helper thread so that the descriptors are closed in
the thread when they are closed elsewhere in UML.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 10 insertions, 9 deletions

diff --git a/arch/um/drivers/chan_user.c b/arch/um/drivers/chan_user.c
index 5d50d4a44abf..2f880cb167a5 100644
--- a/arch/um/drivers/chan_user.c
+++ b/arch/um/drivers/chan_user.c
@@ -9,6 +9,7 @@
 #include <termios.h>
 #include <string.h>
 #include <signal.h>
+#include <sched.h>
 #include <sys/stat.h>
 #include <sys/ioctl.h>
 #include <sys/socket.h>
@@ -73,7 +74,6 @@ static void winch_handler(int sig)
 struct winch_data {
         int pty_fd;
         int pipe_fd;
-        int close_me;
 };
 
 static int winch_thread(void *arg)
@@ -84,7 +84,6 @@ static int winch_thread(void *arg)
         int count, err;
         char c = 1;
 
-        os_close_file(data->close_me);
         pty_fd = data->pty_fd;
         pipe_fd = data->pipe_fd;
         count = os_write_file(pipe_fd, &c, sizeof(c));
@@ -153,15 +152,16 @@ static int winch_tramp(int fd, struct tty_struct *tty, int *fd_out)
         }
 
         data = ((struct winch_data) { .pty_fd           = fd,
-                                      .pipe_fd          = fds[1],
-                                      .close_me         = fds[0] } );
-        err = run_helper_thread(winch_thread, &data, 0, &stack, 0);
+                                      .pipe_fd          = fds[1] } );
+        /* CLONE_FILES so this thread doesn't hold open files which are open
+         * now, but later closed.  This is a problem with /dev/net/tun.
+         */
+        err = run_helper_thread(winch_thread, &data, CLONE_FILES, &stack, 0);
         if(err < 0){
                 printk("fork of winch_thread failed - errno = %d\n", errno);
                 goto out_close;
         }
 
-        os_close_file(fds[1]);
         *fd_out = fds[0];
         n = os_read_file(fds[0], &c, sizeof(c));
         if(n != sizeof(c)){
@@ -169,13 +169,12 @@ static int winch_tramp(int fd, struct tty_struct *tty, int *fd_out)
                 printk("read failed, err = %d\n", -n);
                 printk("fd %d will not support SIGWINCH\n", fd);
                 err = -EINVAL;
-                goto out_close1;
+                goto out_close;
         }
         return err ;
 
  out_close:
         os_close_file(fds[1]);
- out_close1:
         os_close_file(fds[0]);
  out:
         return err;
diff --git a/arch/um/os-Linux/drivers/tuntap_user.c b/arch/um/os-Linux/drivers/tuntap_user.c
index 52945338b64d..87c3aa0252db 100644
--- a/arch/um/os-Linux/drivers/tuntap_user.c
+++ b/arch/um/os-Linux/drivers/tuntap_user.c
@@ -122,6 +122,7 @@ static int tuntap_open_tramp(char *gate, int *fd_out, int me, int remote,
                 return(-EINVAL);
         }
         *fd_out = ((int *) CMSG_DATA(cmsg))[0];
+        os_set_exec_close(*fd_out, 1);
         return(0);
 }
 
@@ -137,7 +138,8 @@ static int tuntap_open(void *data)
                 return(err);
 
         if(pri->fixed_config){
-                pri->fd = os_open_file("/dev/net/tun", of_rdwr(OPENFLAGS()), 0);
+                pri->fd = os_open_file("/dev/net/tun",
+                                       of_cloexec(of_rdwr(OPENFLAGS())), 0);
                 if(pri->fd < 0){
                         printk("Failed to open /dev/net/tun, err = %d\n",
                                -pri->fd);