FAILED: patch "[PATCH] staging: erofs: detect potential multiref due to corrupted" failed to apply to 4.19-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From e12a0ce2fa69798194f3a8628baf6edfbd5c548f Mon Sep 17 00:00:00 2001
From: Gao Xiang <gaoxiang25@xxxxxxxxxx>
Date: Wed, 21 Aug 2019 22:01:52 +0800
Subject: [PATCH] staging: erofs: detect potential multiref due to corrupted
 images

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@xxxxxxxxxxxxxxx> # 4.19+
Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20190821140152.229648-1-gaoxiang25@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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;