On 1/22/23 14:02, Mikulas Patocka wrote:
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.
This patches fixes the bug by testing if the page is equal to ZERO_PAGE(0)
and avoiding the corruption in this case.
Nice catch!
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Sweet Tea Dorminy <sweettea-kernel@xxxxxxxxxx>
---
drivers/md/dm-flakey.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
Index: bcachefs/drivers/md/dm-flakey.c
===================================================================
--- bcachefs.orig/drivers/md/dm-flakey.c 2023-01-22 16:56:35.000000000 +0100
+++ bcachefs/drivers/md/dm-flakey.c 2023-01-22 16:58:40.000000000 +0100
@@ -303,8 +303,11 @@ static void corrupt_bio_data(struct bio
*/
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",
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