[PATCH] erofs: fix folio reuse from a different address_space in erofs_bread()

[Binglei Wang <l3b2w1@gmail.com>]

From: Binglei Wang <l3b2w1@gmail.com>

erofs_bread() reuses a cached folio on page index match without checking folio->mapping.

xattr.c calls erofs_init_metabuf() twice on the same buffer without erofs_put_metabuf();
the two in_metabox sources differ, so buf->mapping can switch
while buf->page still belongs to the old address_space.
The next erofs_bread() then reads the wrong mapping, dropping shared xattrs with METABOX.

We require folio->mapping == buf->mapping in the reuse check;
otherwise drop the cached folio and re-read via the slow path.

Fixes: 414091322c63 ("erofs: implement metadata compression")
Cc: Bo Liu (OpenAnolis) <liubo03@inspur.com>
Signed-off-by: Binglei Wang <l3b2w1@gmail.com>
---
 fs/erofs/data.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/erofs/data.c b/fs/erofs/data.c
index be63b89f0862..d8b6523bc218 100644
--- a/fs/erofs/data.c
+++ b/fs/erofs/data.c
@@ -33,8 +33,13 @@ void *erofs_bread(struct erofs_buf *buf, erofs_off_t offset, bool need_kmap)
 	if (buf->page) {
 		folio = page_folio(buf->page);
-		if (folio_file_page(folio, index) != buf->page)
+		if (folio->mapping != buf->mapping) {
+			/* the cached folio belongs to another address_space */
+			erofs_put_metabuf(buf);
+			folio = NULL;
+		} else if (folio_file_page(folio, index) != buf->page) {
 			erofs_unmap_metabuf(buf);
+		}
 	}
 	if (!folio || !folio_contains(folio, index)) {
 		erofs_put_metabuf(buf);
--
2.43.0