From f50714b57aecb6b3dc81d578e295f86d9c73f078 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka@redhat.com>
Date: Sun, 22 Jan 2023 14:02:57 -0500
Subject: [PATCH] dm flakey: don't corrupt the zero page
Git-commit: f50714b57aecb6b3dc81d578e295f86d9c73f078
Patch-mainline: v6.3-rc1
References: git-fixes
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.
Cc: stable@vger.kernel.org
Fixes: a00f5276e266 ("dm flakey: Properly corrupt multi-page bios.")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Coly Li <colyli@suse.de>
---
drivers/md/dm-flakey.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/md/dm-flakey.c b/drivers/md/dm-flakey.c
index 89fa7a68c6c4..ff9ca5b2a47e 100644
--- a/drivers/md/dm-flakey.c
+++ b/drivers/md/dm-flakey.c
@@ -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",
--
2.35.3