[PATCH] uml: prevent umid theft

Behavior when booting two UMLs with the same umid was broken.  The second one
would steal the umid.  This fixes that, making the second UML take a random
umid instead.

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>

1 files changed, 23 insertions, 10 deletions

diff --git a/arch/um/os-Linux/umid.c b/arch/um/os-Linux/umid.c
index ecf107ae5ac8..198e59163288 100644
--- a/arch/um/os-Linux/umid.c
+++ b/arch/um/os-Linux/umid.c
@@ -143,8 +143,10 @@ static int not_dead_yet(char *dir)
                 goto out_close;
         }
 
-        if((kill(p, 0) == 0) || (errno != ESRCH))
+        if((kill(p, 0) == 0) || (errno != ESRCH)){
+                printk("umid \"%s\" is already in use by pid %d\n", umid, p);
                 return 1;
+        }
 
         err = actually_do_remove(dir);
         if(err)
@@ -234,33 +236,44 @@ int __init make_umid(void)
         err = mkdir(tmp, 0777);
         if(err < 0){
                 err = -errno;
-                if(errno != EEXIST)
+                if(err != -EEXIST)
                         goto err;
 
-                if(not_dead_yet(tmp) < 0)
+                /* 1   -> this umid is already in use
+                 * < 0 -> we couldn't remove the umid directory
+                 * In either case, we can't use this umid, so return -EEXIST.
+                 */
+                if(not_dead_yet(tmp) != 0)
                         goto err;
 
                 err = mkdir(tmp, 0777);
         }
-        if(err < 0){
-                printk("Failed to create '%s' - err = %d\n", umid, err);
-                goto err_rmdir;
+        if(err){
+                err = -errno;
+                printk("Failed to create '%s' - err = %d\n", umid, -errno);
+                goto err;
         }
 
         umid_setup = 1;
 
         create_pid_file();
 
-        return 0;
-
- err_rmdir:
-        rmdir(tmp);
+        err = 0;
  err:
         return err;
 }
 
 static int __init make_umid_init(void)
 {
+        if(!make_umid())
+                return 0;
+
+        /* If initializing with the given umid failed, then try again with
+         * a random one.
+         */
+        printk("Failed to initialize umid \"%s\", trying with a random umid\n",
+               umid);
+        *umid = '\0';
         make_umid();
 
         return 0;