block: check bio split for unaligned bvec

Offsets and lengths need to be validated against the dma alignment. This
check was skipped for sufficiently a small bio with a single bvec, which
may allow an invalid request dispatched to the driver. Force the
validation for an unaligned bvec by forcing the bio split path that
handles this condition.

Fixes: 7eac331 ("iomap: simplify direct io validity check")
Fixes: 5ff3f74 ("block: simplify direct io validity check")
Reported-by: Carlos Maiolino <cem@kernel.org>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Link: https://patch.msgid.link/20260612223205.465913-1-kbusch@meta.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: keithbusch

block/blk.h

@@ -408,6 +408,8 @@ static inline bool bio_may_need_split(struct bio *bio,
 	bv = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
 	if (bio->bi_iter.bi_size > bv->bv_len - bio->bi_iter.bi_bvec_done)
 		return true;
+	if ((bv->bv_offset | bv->bv_len) & lim->dma_alignment)
+		return true;
 	return bv->bv_len + bv->bv_offset > lim->max_fast_segment_size;
 }