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dm-integrity: fix buffer overflow with keyed discard

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Since commit 68c5c42567 ("dm-integrity: replace forgeable discard
filler with a keyed sector marker"), integrity_metadata computes a
checksum for every discarded block into the "checksums" buffer.
integrity_sector_checksum always writes the whole digest. So if the tag
size is smaller than the digest size, the checksum of the last block
that fits into the buffer is written past the end of it. For example,
with hmac(sha256) and tag size 16, a 4MiB discard writes 16 bytes past
the kmalloc'ed page.

Fix this by subtracting extra_space from the buffer size when computing
max_blocks, like we do for writes.

Fixes: 68c5c42567 ("dm-integrity: replace forgeable discard filler with a keyed sector marker")
Reviewed-by: Jose Fernandez (Anthropic) <jose.fernandez@linux.dev>
Signed-off-by: Ben Cressey <ben@cressey.dev>
Assisted-by: Claude:unspecified
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
This commit is contained in:
Ben Cressey 2026-08-20 21:44:57 +00:00 committed by Mikulas Patocka
parent b2fd92f016
commit 59e6f919d7
1 changed files with 1 additions and 1 deletions
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2
drivers/md/dm-integrity.c
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@ -1980,7 +1980,7 @@ 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_blocks = max_size / ic->tag_size;
unsigned int max_blocks = (max_size - extra_space) / ic->tag_size;
sector_t sector = dio->range.logical_sector;
if (!ic->discard_keyed)