From 3cc2810e2d340b7470a84479206446d27d83160f Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Sun, 22 Jan 2023 14:02:57 -0500 Subject: [PATCH] dm flakey: don't corrupt the zero page commit 8594d8276f236c23a4d6685632435f1577787b6e upstream. 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: abd2f25984ab ("dm flakey: Properly corrupt multi-page bios.") Signed-off-by: Mikulas Patocka Reviewed-by: Sweet Tea Dorminy Signed-off-by: Mike Snitzer Signed-off-by: Greg Kroah-Hartman --- 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 220bbf354bb08..805a70abe4376 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", -- 2.39.5