Re: [PATCH v2] md/raid5: Fix UAF on IO across the reshape position

["Yu Kuai" <yukuai@fnnas.com>]

在 2026/4/8 12:35, Benjamin Marzinski 写道:

> 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>
> ---
>
> Changes from v1:
> - Removed mddev->pending_retry_bios, mddev->retry_bios_wait, and
>    md_io_clone->must_retry. Instead, use a completion struct
>    pointed to by bi->bi_private, as suggested by Xiao Ni and Yu Kuai.
>
>   drivers/md/md.c    | 31 ++++++++-----------------------
>   drivers/md/md.h    |  1 -
>   drivers/md/raid5.c |  7 ++++++-
>   3 files changed, 14 insertions(+), 25 deletions(-)
Applied

-- 
Thansk,
Kuai