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: <sta...@vger.kernel.org> # 4.19+
Signed-off-by: Gao Xiang <gaoxian...@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

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