dm-integrity: fix infinite loop on discard with large tag size

Overview

In the Linux kernel, the following vulnerability has been resolved:

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.

Affected

• Linux >= 84597a44a9d86ac949900441cea7da0af0f2f473 < fc512700f1413fed652dac22fa1c4e837210b9c0
• Linux >= 84597a44a9d86ac949900441cea7da0af0f2f473 < 251b44b424920df9204e88a81fb3f78fa48ddd99
• Linux >= 84597a44a9d86ac949900441cea7da0af0f2f473 < 18d80c77b4c7dd20699e81cedfbbff4e9d198f28
• Linux 5.7

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.