linux-kernel - Re: [PATCH 1/4] qla2xxx: Reset done and free callback pointer on release

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Date:   Thu, 27 Aug 2020 12:12:04 +0200
From:   Martin Wilck <mwilck@...e.com>
To:     Daniel Wagner <dwagner@...e.de>, linux-scsi@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Nilesh Javali <njavali@...vell.com>
Subject: Re: [PATCH 1/4] qla2xxx: Reset done and free callback pointer on
 release

On Thu, 2020-08-27 at 11:58 +0200, Daniel Wagner wrote:
> Reset ->done and ->free when releasing the srb. There is a hidden
> use-after-free bug in the driver which corrupts the srb memory pool
> which originates from the cleanup callbacks. By explicitly resetting
> the callbacks to NULL, we workaround the memory corruption.
> 
> An extensive search didn't bring any lights on the real problem. The
> initial idea was to set both pointers to NULL and try to catch
> invalid
> accesses. But instead the memory corruption was gone and the driver
> didn't crash.
> 
> Signed-off-by: Daniel Wagner <dwagner@...e.de>
> ---
>  drivers/scsi/qla2xxx/qla_inline.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/scsi/qla2xxx/qla_inline.h
> b/drivers/scsi/qla2xxx/qla_inline.h
> index 861dc522723c..6d41d758fc17 100644
> --- a/drivers/scsi/qla2xxx/qla_inline.h
> +++ b/drivers/scsi/qla2xxx/qla_inline.h
> @@ -211,6 +211,8 @@ static inline void
>  qla2xxx_rel_qpair_sp(struct qla_qpair *qpair, srb_t *sp)
>  {
>  	sp->qpair = NULL;
> +	sp->done = NULL;
> +	sp->free = NULL;
>  	mempool_free(sp, qpair->srb_mempool);
>  	QLA_QPAIR_MARK_NOT_BUSY(qpair);
>  }

Both sp->done() and sp->free() are called all over the place without
making sure the pointers are non-null. If these functions can be called
for freed sp's, wouldn't that mean we'd crash?

How about setting them to a dummy function that prints a big fat
warning?

Martin