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md/raid5: Fix UAF on IO across the reshape position

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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 <bmarzins@redhat.com>
Reviewed-by: Xiao Ni <xni@redhat.com>
Link: https://lore.kernel.org/r/20260408043548.1695157-1-bmarzins@redhat.com
Signed-off-by: Yu Kuai <yukuai@fnnas.com>
This commit is contained in:
Benjamin Marzinski
2026-04-08 00:35:48 -04:00
committed by Yu Kuai
parent 0898a81762
commit 418b3e64e4
3 changed files with 14 additions and 25 deletions
Download Patch File Download Diff File Expand all files Collapse all files

31
drivers/md/md.c
View File

@@ -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

1
drivers/md/md.h
View File

@@ -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,

7
drivers/md/raid5.c
View File

@@ -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;
}