Unverified Commit 86e87059 authored by Christian Brauner's avatar Christian Brauner
Browse files

eventpoll: move epi_fget() up 

We'll need it when removing files so move it up. No functional change.

Link: https://patch.msgid.link/20260423-work-epoll-uaf-v1-5-2470f9eec0f5@kernel.org


Signed-off-by: default avatarChristian Brauner (Amutable) <brauner@kernel.org>
parent 0bade234

fs/eventpoll.c

+28 −28
Original line number Diff line number Diff line
@@ -826,6 +826,34 @@ static void ep_free(struct eventpoll *ep) 
	kfree_rcu(ep, rcu);

}



/*

 * The ffd.file pointer may be in the process of being torn down due to

 * being closed, but we may not have finished eventpoll_release() yet.

 *

 * Normally, even with the atomic_long_inc_not_zero, the file may have

 * been free'd and then gotten re-allocated to something else (since

 * files are not RCU-delayed, they are SLAB_TYPESAFE_BY_RCU).

 *

 * But for epoll, users hold the ep->mtx mutex, and as such any file in

 * the process of being free'd will block in eventpoll_release_file()

 * and thus the underlying file allocation will not be free'd, and the

 * file re-use cannot happen.

 *

 * For the same reason we can avoid a rcu_read_lock() around the

 * operation - 'ffd.file' cannot go away even if the refcount has

 * reached zero (but we must still not call out to ->poll() functions

 * etc).

 */

static struct file *epi_fget(const struct epitem *epi)

{

	struct file *file;



	file = epi->ffd.file;

	if (!file_ref_get(&file->f_ref))

		file = NULL;

	return file;

}



/*

 * Called with &file->f_lock held,

 * returns with it released
@@ -1018,34 +1046,6 @@ static __poll_t __ep_eventpoll_poll(struct file *file, poll_table *wait, int dep 
	return res;

}



/*

 * The ffd.file pointer may be in the process of being torn down due to

 * being closed, but we may not have finished eventpoll_release() yet.

 *

 * Normally, even with the atomic_long_inc_not_zero, the file may have

 * been free'd and then gotten re-allocated to something else (since

 * files are not RCU-delayed, they are SLAB_TYPESAFE_BY_RCU).

 *

 * But for epoll, users hold the ep->mtx mutex, and as such any file in

 * the process of being free'd will block in eventpoll_release_file()

 * and thus the underlying file allocation will not be free'd, and the

 * file re-use cannot happen.

 *

 * For the same reason we can avoid a rcu_read_lock() around the

 * operation - 'ffd.file' cannot go away even if the refcount has

 * reached zero (but we must still not call out to ->poll() functions

 * etc).

 */

static struct file *epi_fget(const struct epitem *epi)

{

	struct file *file;



	file = epi->ffd.file;

	if (!file_ref_get(&file->f_ref))

		file = NULL;

	return file;

}



/*

 * Differs from ep_eventpoll_poll() in that internal callers already have

 * the ep->mtx so we need to start from depth=1, such that mutex_lock_nested()