[PATCH] close race in unshare_files()

updating current->files requires task_lock

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 9 insertions, 11 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 89fe414645e9..76f05a08062b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -805,12 +805,6 @@ static int copy_files(unsigned long clone_flags, struct task_struct * tsk)
                 goto out;
         }
 
-        /*
-         * Note: we may be using current for both targets (See exec.c)
-         * This works because we cache current->files (old) as oldf. Don't
-         * break this.
-         */
-        tsk->files = NULL;
         newf = dup_fd(oldf, &error);
         if (!newf)
                 goto out;
@@ -855,7 +849,8 @@ static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
 int unshare_files(void)
 {
         struct files_struct *files  = current->files;
-        int rc;
+        struct files_struct *newf;
+        int error = 0;
 
         BUG_ON(!files);
 
@@ -866,10 +861,13 @@ int unshare_files(void)
                 atomic_inc(&files->count);
                 return 0;
         }
-        rc = copy_files(0, current);
-        if(rc)
-                current->files = files;
-        return rc;
+        newf = dup_fd(files, &error);
+        if (newf) {
+                task_lock(current);
+                current->files = newf;
+                task_unlock(current);
+        }
+        return error;
 }
 
 EXPORT_SYMBOL(unshare_files);