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Commit 3b125388 authored by Al Viro's avatar Al Viro
Browse files

[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: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent fd8328be

fs/exec.c

+6 −12
Original line number Diff line number Diff line
@@ -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;

}

include/linux/file.h

+2 −1
Original line number Diff line number Diff line
@@ -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;

include/linux/fs.h

+0 −3
Original line number Diff line number Diff line
@@ -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 */



/*

kernel/exit.c

+2 −1
Original line number Diff line number Diff line
@@ -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;

kernel/fork.c

+24 −30
Original line number Diff line number Diff line
@@ -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;

}