[PATCH] fuse: validate folio state before pipe_buf_try_steal() in fuse_try_move_folio()

[Hui Peng <benquike@gmail.com>]

In fuse_try_move_folio(), check that the pipe buffer's folio is not
hugetlb, swap-backed, or already mapped/anon before attempting
pipe_buf_try_steal() and inserting it into the FUSE inode's page cache,
preventing VM_BUG_ON_FOLIO() and page cache state corruption.

Fixes: 394244b24fdd ("fuse: support copying large folios")
Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@gmail.com>
---
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 4fec31fc0b84..121bb1f3cb05 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1147,32 +1147,32 @@ static int fuse_try_move_folio(struct fuse_copy_state *cs, struct folio **foliop
 	if (cs->len != folio_size(oldfolio))
 		goto out_fallback;
 
-	if (!pipe_buf_try_steal(cs->pipe, buf))
-		goto out_fallback;
-
 	newfolio = page_folio(buf->page);
 
-	folio_clear_uptodate(newfolio);
-	folio_clear_mappedtodisk(newfolio);
-
 	if (folio_test_large(newfolio))
-		goto out_fallback_unlock;
-
-	if (fuse_check_folio(newfolio) != 0)
-		goto out_fallback_unlock;
+		goto out_fallback;
 
 	/*
 	 * This is a new and locked page, it shouldn't be mapped or
 	 * have any special flags on it
 	 */
 	if (WARN_ON(folio_mapped(oldfolio)))
-		goto out_fallback_unlock;
+		goto out_fallback;
 	if (WARN_ON(folio_has_private(oldfolio)))
-		goto out_fallback_unlock;
+		goto out_fallback;
 	if (WARN_ON(folio_test_dirty(oldfolio) ||
 				folio_test_writeback(oldfolio)))
-		goto out_fallback_unlock;
+		goto out_fallback;
 	if (WARN_ON(folio_test_mlocked(oldfolio)))
+		goto out_fallback;
+
+	if (!pipe_buf_try_steal(cs->pipe, buf))
+		goto out_fallback;
+
+	folio_clear_uptodate(newfolio);
+	folio_clear_mappedtodisk(newfolio);
+
+	if (fuse_check_folio(newfolio) != 0)
 		goto out_fallback_unlock;
 
 	err = lock_request(cs->req);