FAILED: patch "[PATCH] dm flakey: don't corrupt the zero page" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-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 <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x f50714b57aecb6b3dc81d578e295f86d9c73f078
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '[email protected]' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:

f50714b57aec ("dm flakey: don't corrupt the zero page")

thanks,

greg k-h

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

From f50714b57aecb6b3dc81d578e295f86d9c73f078 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <[email protected]>
Date: Sun, 22 Jan 2023 14:02:57 -0500
Subject: [PATCH] dm flakey: don't corrupt the zero page

When we need to zero some range on a block device, the function __blkdev_issue_zero_pages submits a write bio with the bio vector pointing to the zero page. If we use dm-flakey with corrupt bio writes option, it will corrupt the content of the zero page which results in crashes of various userspace programs. Glibc assumes that memory returned by mmap is zeroed and it uses it for calloc implementation; if the newly mapped memory is not zeroed, calloc will return non-zeroed memory.

Fix this bug by testing if the page is equal to ZERO_PAGE(0) and avoiding the corruption in this case.

index 89fa7a68c6c4..ff9ca5b2a47e 100644
@@ -303,8 +303,11 @@ static void corrupt_bio_data(struct bio *bio, struct flakey_c *fc)
 	 */
 	bio_for_each_segment(bvec, bio, iter) {
 		if (bio_iter_len(bio, iter) > corrupt_bio_byte) {
-			char *segment = (page_address(bio_iter_page(bio, iter))
-					 + bio_iter_offset(bio, iter));
+			char *segment;
+			struct page *page = bio_iter_page(bio, iter);
+			if (unlikely(page == ZERO_PAGE(0)))
+				break;
+			segment = (page_address(page) + bio_iter_offset(bio, iter));
 			segment[corrupt_bio_byte] = fc->corrupt_bio_value;
 			DMDEBUG("Corrupting data bio=%p by writing %u to byte %u "
 				"(rw=%c bi_opf=%u bi_sector=%llu size=%u)\n",