[PATCH v2 5/6] staging: erofs: detect potential multiref due to corrupted images

[Gao Xiang]

As reported by erofs-utils fuzzer, currently, multiref
(ondisk deduplication) hasn't been supported for now,
we should forbid it properly.

Fixes: 3883a79abd02 ("staging: erofs: introduce VLE decompression support")
Cc: <stable at vger.kernel.org> # 4.19+
Signed-off-by: Gao Xiang <gaoxiang25 at huawei.com>
---

changelog from v1:
 - change err = -EFSCORRUPTED as well as Chao suggested;
   [ the difference between adding err or not to [PATCH 5/6] is just whether
     we error out the whole compressed cluster or partial of them (since some
     pages could be decompressed successfully), it's an undefined behavior
     for these corrupted compressed images... ]

Hi Chao,
 Could you kindly review it again? Thanks!

Hi Greg,
 This is [PATCH 5/6] of the original patchset, and I fix as what Chao suggested...
 But I'm not sure whether it should be merged right now, it is up to you. :)

Thanks,
Gao Xiang


 drivers/staging/erofs/zdata.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/erofs/zdata.c b/drivers/staging/erofs/zdata.c
index 4d6faaab04f5..60d7c20db87d 100644
--- a/drivers/staging/erofs/zdata.c
+++ b/drivers/staging/erofs/zdata.c
@@ -798,6 +798,7 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
 	for (i = 0; i < nr_pages; ++i)
 		pages[i] = NULL;
 
+	err = 0;
 	z_erofs_pagevec_ctor_init(&ctor, Z_EROFS_NR_INLINE_PAGEVECS,
 				  cl->pagevec, 0);
 
@@ -819,8 +820,17 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
 			pagenr = z_erofs_onlinepage_index(page);
 
 		DBG_BUGON(pagenr >= nr_pages);
-		DBG_BUGON(pages[pagenr]);
 
+		/*
+		 * currently EROFS doesn't support multiref(dedup),
+		 * so here erroring out one multiref page.
+		 */
+		if (unlikely(pages[pagenr])) {
+			DBG_BUGON(1);
+			SetPageError(pages[pagenr]);
+			z_erofs_onlinepage_endio(pages[pagenr]);
+			err = -EFSCORRUPTED;
+		}
 		pages[pagenr] = page;
 	}
 	z_erofs_pagevec_ctor_exit(&ctor, true);
@@ -828,7 +838,6 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
 	overlapped = false;
 	compressed_pages = pcl->compressed_pages;
 
-	err = 0;
 	for (i = 0; i < clusterpages; ++i) {
 		unsigned int pagenr;
 
@@ -852,7 +861,12 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
 			pagenr = z_erofs_onlinepage_index(page);
 
 			DBG_BUGON(pagenr >= nr_pages);
-			DBG_BUGON(pages[pagenr]);
+			if (unlikely(pages[pagenr])) {
+				DBG_BUGON(1);
+				SetPageError(pages[pagenr]);
+				z_erofs_onlinepage_endio(pages[pagenr]);
+				err = -EFSCORRUPTED;
+			}
 			pages[pagenr] = page;
 
 			overlapped = true;
-- 
2.17.1