linux-kernel - Re: [PATCH] block, bfq: fix waker_bfqq UAF after bfq_split

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Message-ID: <syxzk4eauh3zzs37y6eirzlblp5lin6wyrpanw2mleliyj6cnr@2y3a7hrnet2o>
Date: Thu, 9 Jan 2025 09:50:51 +0100
From: Jan Kara <jack@...e.cz>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: Jan Kara <jack@...e.cz>, axboe@...nel.dk, linux-block@...r.kernel.org, 
	linux-kernel@...r.kernel.org, yi.zhang@...wei.com, yangerkun@...wei.com, 
	"yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] block, bfq: fix waker_bfqq UAF after bfq_split_bfqq()

On Thu 09-01-25 09:32:08, Yu Kuai wrote:
> Hi,
> 
> 在 2025/01/08 22:42, Jan Kara 写道:
> > 
> > 
> > >   			 */
> > >   			if (bfqq_process_refs(waker_bfqq) == 1)
> > >   				return NULL;
> > > -			break;
> > > +
> > > +			return waker_bfqq;
> > 
> > So how do you know bfqq_process_refs(waker_bfqq) is not 0 in this case?
> 
> Because in this case, waker_bfqq is in the merge chain of bfqq, and bfqq
> is obtained frm the current process, which means waker_bfqq should have
> at least one process reference that is from current thread.

Ah, right. Thanks for explanation. The except for the typo the patch looks
good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

(although I can see Jens has already picked up the patch so probably this
is immaterial).

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR