From 418b3e64e4459feb3f75979de9ec89e085745343 Mon Sep 17 00:00:00 2001 From: Benjamin Marzinski Date: Wed, 8 Apr 2026 00:35:48 -0400 Subject: [PATCH] md/raid5: Fix UAF on IO across the reshape position If make_stripe_request() returns STRIPE_WAIT_RESHAPE, raid5_make_request() will free the cloned bio. But raid5_make_request() can call make_stripe_request() multiple times, writing to the various stripes. If that bio got added to the toread or towrite lists of a stripe disk in an earlier call to make_stripe_request(), then it's not safe to just free the bio if a later part of it is found to cross the reshape position. Doing so can lead to a UAF error, when bio_endio() is called on the bio for the earlier stripes. Instead, raid5_make_request() needs to wait until all parts of the bio have called bio_endio(). To do this, bios that cross the reshape position while the reshape can't make progress are flagged as needing to wait for all parts to complete. When raid5_make_request() has a bio that failed make_stripe_request() with STRIPE_WAIT_RESHAPE, it sets bi->bi_private to a completion struct and waits for completion after ending the bio. When the bio_endio() is called for the last time on a clone bio with bi->bi_private set, it wakes up the waiter. This guarantees that raid5_make_request() doesn't return until the cloned bio needing a retry for io across the reshape boundary is safely cleaned up. There is a simple reproducer available at [1]. Compile the kernel with KASAN for more useful reporting when the error is triggered (this is not necessary to see the bug). [1] https://gist.github.com/bmarzins/e48598824305cf2171289e47d7241fa5 Signed-off-by: Benjamin Marzinski Reviewed-by: Xiao Ni Link: https://lore.kernel.org/r/20260408043548.1695157-1-bmarzins@redhat.com Signed-off-by: Yu Kuai --- drivers/md/md.c | 31 ++++++++----------------------- drivers/md/md.h | 1 - drivers/md/raid5.c | 7 ++++++- 3 files changed, 14 insertions(+), 25 deletions(-) diff --git a/drivers/md/md.c b/drivers/md/md.c index 5fb5ae8368ba..8656f2eff40d 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -9341,9 +9341,11 @@ static void md_bitmap_end(struct mddev *mddev, struct md_io_clone *md_io_clone) static void md_end_clone_io(struct bio *bio) { - struct md_io_clone *md_io_clone = bio->bi_private; + struct md_io_clone *md_io_clone = container_of(bio, struct md_io_clone, + bio_clone); struct bio *orig_bio = md_io_clone->orig_bio; struct mddev *mddev = md_io_clone->mddev; + struct completion *reshape_completion = bio->bi_private; if (bio_data_dir(orig_bio) == WRITE && md_bitmap_enabled(mddev, false)) md_bitmap_end(mddev, md_io_clone); @@ -9355,7 +9357,10 @@ static void md_end_clone_io(struct bio *bio) bio_end_io_acct(orig_bio, md_io_clone->start_time); bio_put(bio); - bio_endio(orig_bio); + if (unlikely(reshape_completion)) + complete(reshape_completion); + else + bio_endio(orig_bio); percpu_ref_put(&mddev->active_io); } @@ -9380,7 +9385,7 @@ static void md_clone_bio(struct mddev *mddev, struct bio **bio) } clone->bi_end_io = md_end_clone_io; - clone->bi_private = md_io_clone; + clone->bi_private = NULL; *bio = clone; } @@ -9391,26 +9396,6 @@ void md_account_bio(struct mddev *mddev, struct bio **bio) } EXPORT_SYMBOL_GPL(md_account_bio); -void md_free_cloned_bio(struct bio *bio) -{ - struct md_io_clone *md_io_clone = bio->bi_private; - struct bio *orig_bio = md_io_clone->orig_bio; - struct mddev *mddev = md_io_clone->mddev; - - if (bio_data_dir(orig_bio) == WRITE && md_bitmap_enabled(mddev, false)) - md_bitmap_end(mddev, md_io_clone); - - if (bio->bi_status && !orig_bio->bi_status) - orig_bio->bi_status = bio->bi_status; - - if (md_io_clone->start_time) - bio_end_io_acct(orig_bio, md_io_clone->start_time); - - bio_put(bio); - percpu_ref_put(&mddev->active_io); -} -EXPORT_SYMBOL_GPL(md_free_cloned_bio); - /* md_allow_write(mddev) * Calling this ensures that the array is marked 'active' so that writes * may proceed without blocking. It is important to call this before diff --git a/drivers/md/md.h b/drivers/md/md.h index d6f5482e2479..12d86aa7e6f9 100644 --- a/drivers/md/md.h +++ b/drivers/md/md.h @@ -920,7 +920,6 @@ extern void md_finish_reshape(struct mddev *mddev); void md_submit_discard_bio(struct mddev *mddev, struct md_rdev *rdev, struct bio *bio, sector_t start, sector_t size); void md_account_bio(struct mddev *mddev, struct bio **bio); -void md_free_cloned_bio(struct bio *bio); extern bool __must_check md_flush_request(struct mddev *mddev, struct bio *bio); void md_write_metadata(struct mddev *mddev, struct md_rdev *rdev, diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index 6e79829c5acb..0d76e82f4506 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -6217,7 +6217,12 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi) mempool_free(ctx, conf->ctx_pool); if (res == STRIPE_WAIT_RESHAPE) { - md_free_cloned_bio(bi); + DECLARE_COMPLETION_ONSTACK(done); + WRITE_ONCE(bi->bi_private, &done); + + bio_endio(bi); + + wait_for_completion(&done); return false; }