FAILED: patch "[PATCH] dm-integrity: fix infinite loop on discard with large tag" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-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-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 18d80c77b4c7dd20699e81cedfbbff4e9d198f28
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026102106-hacker-likely-7fd3@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 18d80c77b4c7dd20699e81cedfbbff4e9d198f28 Mon Sep 17 00:00:00 2001
From: Ben Cressey <[email protected]>
Date: Thu, 20 Aug 2026 21:44:58 +0000
Subject: [PATCH] dm-integrity: fix infinite loop on discard with large tag
size

When integrity_metadata handles a discard, it fills a buffer with DISCARD_FILLER and writes it over the tags, max_blocks blocks at a time. If the kmalloc fails, the buffer is the on-stack array checksums_onstack and max_size is set to HASH_MAX_DIGESTSIZE. So if the tag size is larger than HASH_MAX_DIGESTSIZE, max_blocks is zero, bi_size is never decremented and the loop never terminates.

Fix this by using sizeof(checksums_onstack) as max_size. The array has MAX_TAG_SIZE bytes since commit b93b6643e9b5 ("dm integrity: fix a crash with unusually large tag size"), so max_blocks is at least 1.

index d4fe85d61d33..5327d7c6a71c 100644
@@ -1979,7 +1979,7 @@ static void integrity_metadata(struct work_struct *w)
 
 		if (unlikely(dio->op == REQ_OP_DISCARD)) {
 			unsigned int bi_size = dio->bio_details.bi_iter.bi_size;
-			unsigned int max_size = likely(checksums != checksums_onstack) ? PAGE_SIZE : HASH_MAX_DIGESTSIZE;
+			unsigned int max_size = likely(checksums != checksums_onstack) ? PAGE_SIZE : sizeof(checksums_onstack);
 			unsigned int max_blocks = (max_size - extra_space) / ic->tag_size;
 			sector_t sector = dio->range.logical_sector;
 

From: Ben Cressey <[email protected]>

[ Upstream commit 18d80c77b4c7dd20699e81cedfbbff4e9d198f28 ]

When integrity_metadata handles a discard, it fills a buffer with DISCARD_FILLER and writes it over the tags, max_blocks blocks at a time. If the kmalloc fails, the buffer is the on-stack array checksums_onstack and max_size is set to HASH_MAX_DIGESTSIZE. So if the tag size is larger than HASH_MAX_DIGESTSIZE, max_blocks is zero, bi_size is never decremented and the loop never terminates.

Fix this by using sizeof(checksums_onstack) as max_size. The array has MAX_TAG_SIZE bytes since commit b93b6643e9b5 ("dm integrity: fix a crash with unusually large tag size"), so max_blocks is at least 1.

---
 drivers/md/dm-integrity.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index aa6f3e71c4fa2..74cce5111637f 100644
@@ -1814,7 +1814,7 @@ static void integrity_metadata(struct work_struct *w)
 
 		if (unlikely(dio->op == REQ_OP_DISCARD)) {
 			unsigned int bi_size = dio->bio_details.bi_iter.bi_size;
-			unsigned int max_size = likely(checksums != checksums_onstack) ? PAGE_SIZE : HASH_MAX_DIGESTSIZE;
+			unsigned int max_size = likely(checksums != checksums_onstack) ? PAGE_SIZE : sizeof(checksums_onstack);
 			unsigned int max_blocks = max_size / ic->tag_size;
 
 			memset(checksums, DISCARD_FILLER, max_size);

2.53.0