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Subject[PATCH v2 5/6] staging: erofs: detect potential multiref due to corrupted images
Date
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@vger.kernel.org> # 4.19+
Signed-off-by: Gao Xiang <gaoxiang25@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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