linux-ext4 - Re: [PATCH] ext4: fix memory leak in ext4_fill

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Date:   Fri, 30 Apr 2021 01:05:47 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     "Theodore Ts'o" <tytso@....edu>
Cc:     Vegard Nossum <vegard.nossum@...cle.com>,
        akpm@...ux-foundation.org, peterz@...radead.org, axboe@...nel.dk,
        pmladek@...e.com, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzbot+d9e482e303930fa4f6ff@...kaller.appspotmail.com
Subject: Re: [PATCH] ext4: fix memory leak in ext4_fill_super

On Thu, 29 Apr 2021 17:41:12 -0400
"Theodore Ts'o" <tytso@....edu> wrote:

> On Thu, Apr 29, 2021 at 11:09:56PM +0300, Pavel Skripkin wrote:
> > > we will exit with -ENOMEM.  So at the very least all callers of
> > > kthread_stop() also need to check for -ENOMEM as well as -EINTR
> > > --- or, be somehow sure that the thread function was successfully
> > > called and started.  In this particular case, the ext4 mount code
> > > had just started the kmmpd thread, and then detected that
> > > something else had gone wrong, and failed the mount before the
> > > kmmpd thread ever had a chance to run.
> > 
> > There is a small problem about -ENOMEM...
> 
> What I'd suggest is that we simply move
> 
> > exit_thread:
> > 	EXT4_SB(sb)->s_mmp_tsk = NULL;
> > 	kfree(data);
> > 	brelse(bh);
> > 	return retval;
> > }
> 
> out of the thread function.  That means hanging struct mmpd_data off
> the struct ext4_sb_info structure, and then adding a function like
> this to fs/ext4/mmp.c
> 
> static void ext4_stop_mmpd(struct ext4_sb_info *sbi)
> {
> 	if (sbi->s_mmp_tsk) {
> 		kthread_stop(sbi->s_mmp_tsk);
> 		brelse(sbi->s_mmp_data->bh);
> 		kfree(sbi->s_mmp_data);
> 		sbi->s_mmp_data = NULL;
> 		sbi->s_mmp_tsk = NULL;
> 	}
> }
> 
> Basically, just move all of the cleanup so it is done after the
> kthread is stopped, so we don't have to do any fancy error checking.
> We just do it unconditionally.

This sound much better than my idea. Will do it in v2.

Thanks!

> 
> 					- Ted
> 
> P.S.  Actually, we could drop the struct mmpd_data altogether, and
> just hang the buffer head as sbi->s_mmp_bh.  Then we can just pass the
> struct super * as the private pointer to kmmpd().
> 



With regards,
Pavel Skripkin