[PATCH] sanitize unshare_files/reset_files_struct

* let unshare_files() give caller the displaced files_struct
* don't bother with grabbing reference only to drop it in the
  caller if it hadn't been shared in the first place
* in that form unshare_files() is trivially implemented via
  unshare_fd(), so we eliminate the duplicate logics in fork.c
* reset_files_struct() is not just only called for current;
  it will break the system if somebody ever calls it for anything
  else (we can't modify ->files of somebody else).  Lose the
  task_struct * argument.

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

diff --git a/fs/exec.c b/fs/exec.c
index 4755430..b152029 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1269,19 +1269,13 @@ int do_execve(char * filename,
        struct linux_binprm *bprm;
        struct file *file;
        unsigned long env_p;
-       struct files_struct *files;
+       struct files_struct *displaced;
        int retval;
 
-       files = current->files;
-       retval = unshare_files();
+       retval = unshare_files(&displaced);
        if (retval)
                goto out_ret;
 
-       if (files == current->files) {
-               put_files_struct(files);
-               files = NULL;
-       }
-
        retval = -ENOMEM;
        bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
        if (!bprm)
@@ -1340,8 +1334,8 @@ int do_execve(char * filename,
                security_bprm_free(bprm);
                acct_update_integrals(current);
                kfree(bprm);
-               if (files)
-                       put_files_struct(files);
+               if (displaced)
+                       put_files_struct(displaced);
                return retval;
        }
 
@@ -1363,8 +1357,8 @@ out_kfree:
        kfree(bprm);
 
 out_files:
-       if (files)
-               reset_files_struct(current, files);
+       if (displaced)
+               reset_files_struct(displaced);
 out_ret:
        return retval;
 }

diff --git a/include/linux/file.h b/include/linux/file.h
index 6534770..69baf5a 100644 (file)
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -117,7 +117,8 @@ struct task_struct;
 
 struct files_struct *get_files_struct(struct task_struct *);
 void put_files_struct(struct files_struct *fs);
-void reset_files_struct(struct task_struct *, struct files_struct *);
+void reset_files_struct(struct files_struct *);
+int unshare_files(struct files_struct **);
 
 extern struct kmem_cache *files_cachep;
 

diff --git a/include/linux/fs.h b/include/linux/fs.h
index ad41d0b..e057438 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2033,9 +2033,6 @@ static inline ino_t parent_ino(struct dentry *dentry)
        return res;
 }
 
-/* kernel/fork.c */
-extern int unshare_files(void);
-
 /* Transaction based IO helpers */
 
 /*

diff --git a/kernel/exit.c b/kernel/exit.c
index 3d32000..97f609f 100644 (file)
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -507,8 +507,9 @@ void put_files_struct(struct files_struct *files)
        }
 }
 
-void reset_files_struct(struct task_struct *tsk, struct files_struct *files)
+void reset_files_struct(struct files_struct *files)
 {
+       struct task_struct *tsk = current;
        struct files_struct *old;
 
        old = tsk->files;

diff --git a/kernel/fork.c b/kernel/fork.c
index 2fc11f2..efb618f 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -840,36 +840,6 @@ static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
        return 0;
 }
 
-/*
- *     Helper to unshare the files of the current task.
- *     We don't want to expose copy_files internals to
- *     the exec layer of the kernel.
- */
-
-int unshare_files(void)
-{
-       struct files_struct *files  = current->files;
-       struct files_struct *newf;
-       int error = 0;
-
-       BUG_ON(!files);
-
-       /* This can race but the race causes us to copy when we don't
-          need to and drop the copy */
-       if(atomic_read(&files->count) == 1)
-       {
-               atomic_inc(&files->count);
-               return 0;
-       }
-       newf = dup_fd(files, &error);
-       if (newf) {
-               task_lock(current);
-               current->files = newf;
-               task_unlock(current);
-       }
-       return error;
-}
-
 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
 {
        struct sighand_struct *sig;
@@ -1807,3 +1777,27 @@ bad_unshare_cleanup_thread:
 bad_unshare_out:
        return err;
 }
+
+/*
+ *     Helper to unshare the files of the current task.
+ *     We don't want to expose copy_files internals to
+ *     the exec layer of the kernel.
+ */
+
+int unshare_files(struct files_struct **displaced)
+{
+       struct task_struct *task = current;
+       struct files_struct *copy;
+       int error;
+
+       error = unshare_fd(CLONE_FILES, &copy);
+       if (error || !copy) {
+               *displaced = NULL;
+               return error;
+       }
+       *displaced = task->files;
+       task_lock(task);
+       task->files = copy;
+       task_unlock(task);
+       return 0;
+}