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, 8 insertions, 1 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index d6e062c42a8d..b0b3792b1496 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -719,8 +719,15 @@ void mmb_mark_buffer_dirty(struct buffer_head *bh,
 	mark_buffer_dirty(bh);
 	if (!bh->b_mmb) {
 		spin_lock(&mmb->lock);
+		/*
+		 * For a corrupted filesystem with multiply claimed blocks this
+		 * can fail. Avoid corrupting the linked list in that case.
+		 */
+		if (cmpxchg(&bh->b_mmb, NULL, mmb) != NULL) {
+			spin_unlock(&mmb->lock);
+			return;
+		}
 		list_move_tail(&bh->b_assoc_buffers, &mmb->list);
-		bh->b_mmb = mmb;
 		spin_unlock(&mmb->lock);
 	}
 }