[PATCH] dm era: fix out-of-bounds memory access for non-zero start sector

dm-era tracks writes in target-relative blocks, but era_map() calculates
the writeset block before applying the target offset.  Tables with a
non-zero start sector can therefore pass an absolute mapped-device block
to metadata_current_marked().

If the absolute block is beyond the current writeset size,
writeset_marked() tests past the end of the in-core bitset.  KASAN reports
this as a vmalloc-out-of-bounds access.

Apply the target offset before calculating the era block so writeset
lookups use the target-relative block number.

Assisted-by: Codex:gpt-5.5-cyber-preview
Signed-off-by: Samuel Moelius <[email protected]>
---
 drivers/md/dm-era-target.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-era-target.c b/drivers/md/dm-era-target.c
index 05285c04ff2c..18aed0e2a508 100644
--- a/drivers/md/dm-era-target.c
+++ b/drivers/md/dm-era-target.c
@@ -1229,6 +1229,7 @@ static dm_block_t get_block(struct era *era, struct bio *bio)
 static void remap_to_origin(struct era *era, struct bio *bio)
 {
 	bio_set_dev(bio, era->origin_dev->bdev);
+	bio->bi_iter.bi_sector = dm_target_offset(era->ti, bio->bi_iter.bi_sector);
 }
 
 /*
@@ -1560,7 +1561,7 @@ static void era_dtr(struct dm_target *ti)
 static int era_map(struct dm_target *ti, struct bio *bio)
 {
 	struct era *era = ti->private;
-	dm_block_t block = get_block(era, bio);
+	dm_block_t block;
 
 	/*
 	 * All bios get remapped to the origin device.  We do this now, but
@@ -1568,6 +1569,7 @@ static int era_map(struct dm_target *ti, struct bio *bio)
 	 * block is marked in this era.
 	 */
 	remap_to_origin(era, bio);
+	block = get_block(era, bio);
 
 	/*
 	 * REQ_PREFLUSH bios carry no data, so we're not interested in them.
-- 
2.43.0