iomap: keep large chunks from defeating the bio cap

For integrity I/O a bio must not grow beyond max_integrity_io_size()
because the integrity buffer is a single allocation of at most 2 MiB.
Writeback and buffered reads check that before adding to a bio:

        bio->bi_iter.bi_size > iomap_max_bio_size(iomap) - len

The subtraction is done in size_t and wraps if len alone is above the
limit. The check then never fires and the bio grows until it runs out
of bio_vecs.

That's easy to hit. The limit is also capped by the maximum segment size
which is 64 KiB for SCSI hosts that don't set it, such as lpfc and
qla2xxx, and XFS uses folios of up to 2 MiB. Writeback of a preallocated
300 MiB file then builds a single bio that needs 4.7 MiB of PI with 512
byte sectors and 8 byte tuples. That's more than kmalloc() can do, so
bio_integrity_alloc_buf() falls back to a 2 MiB mempool element and
generating the PI writes 2.7 MiB past its end.

Check the length on its own first. A chunk above the limit still gets a
bio of its own which is never larger than a folio.

Fixes: 0b10a370529c ("iomap: support T10 protection information")
Cc: stable@vger.kernel.org # v7.1+
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Link: https://patch.msgid.link/20261029-work-iomap-ai-fixes-v1-2-7eda63bc1b13@kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions