Merge tag 'vfs-7.1-rc1.fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull vfs fixes from Christian Brauner:

 - eventpoll: fix ep_remove() UAF and follow-up cleanup

 - fs: aio: set VMA_DONTCOPY_BIT in mmap to fix NULL-pointer-dereference
   error

 - writeback: Fix use after free in inode_switch_wbs_work_fn()

 - fuse: reject oversized dirents in page cache

 - fs: aio: reject partial mremap to avoid Null-pointer-dereference
   error

 - nstree: fix func. parameter kernel-doc warnings

 - fs: Handle multiply claimed blocks more gracefully with mmb

* tag 'vfs-7.1-rc1.fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  eventpoll: drop vestigial epi->dying flag
  eventpoll: drop dead bool return from ep_remove_epi()
  eventpoll: refresh eventpoll_release() fast-path comment
  eventpoll: move f_lock acquisition into ep_remove_file()
  eventpoll: fix ep_remove struct eventpoll / struct file UAF
  eventpoll: move epi_fget() up
  eventpoll: rename ep_remove_safe() back to ep_remove()
  eventpoll: drop vestigial __ prefix from ep_remove_{file,epi}()
  eventpoll: kill __ep_remove()
  eventpoll: split __ep_remove()
  eventpoll: use hlist_is_singular_node() in __ep_remove()
  fs: Handle multiply claimed blocks more gracefully with mmb
  nstree: fix func. parameter kernel-doc warnings
  fs: aio: reject partial mremap to avoid Null-pointer-dereference error
  fuse: reject oversized dirents in page cache
  writeback: Fix use after free in inode_switch_wbs_work_fn()
  fs: aio: set VMA_DONTCOPY_BIT in mmap to fix NULL-pointer-dereference error

1 files changed, 10 insertions, 6 deletions

diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h
index ea9ca0e4172a..728fb5dee5ed 100644
--- a/include/linux/eventpoll.h
+++ b/include/linux/eventpoll.h
@@ -39,12 +39,16 @@ static inline void eventpoll_release(struct file *file)
 {
 
 	/*
-	 * Fast check to avoid the get/release of the semaphore. Since
-	 * we're doing this outside the semaphore lock, it might return
-	 * false negatives, but we don't care. It'll help in 99.99% of cases
-	 * to avoid the semaphore lock. False positives simply cannot happen
-	 * because the file in on the way to be removed and nobody ( but
-	 * eventpoll ) has still a reference to this file.
+	 * Fast check to skip the slow path in the common case where the
+	 * file was never attached to an epoll. Safe without file->f_lock
+	 * because every f_ep writer excludes a concurrent __fput() on
+	 * @file:
+	 *   - ep_insert() requires the file alive (refcount > 0);
+	 *   - ep_remove() holds @file pinned via epi_fget() across the
+	 *     write;
+	 *   - eventpoll_release_file() runs from __fput() itself.
+	 * We are in __fput() here, so none of those can race us: a NULL
+	 * observation truly means no epoll path has work left on @file.
 	 */
 	if (likely(!READ_ONCE(file->f_ep)))
 		return;