From: Jan Kara <jack@suse.cz>
To: "zhangyi (F)" <yi.zhang@huawei.com>
Cc: "Theodore Y. Ts'o" <tytso@mit.edu>,
linux-ext4@vger.kernel.org, jack@suse.cz,
adilger.kernel@dilger.ca
Subject: Re: [PATCH v5] ext4: fix potential use after free in system zone via remount with noblock_validity
Date: Mon, 26 Aug 2019 17:03:50 +0200 [thread overview]
Message-ID: <20190826150350.GH10614@quack2.suse.cz> (raw)
In-Reply-To: <33767946-1e6f-5165-94b3-46e2da15172f@huawei.com>
On Mon 26-08-19 16:31:41, zhangyi (F) wrote:
> On 2019/8/26 10:56, Theodore Y. Ts'o Wrote:
> > I added a missing rcu_read_lock() to prevent a suspicious RCU
> > warning when CONFIG_PROVE_RCU is enabled:
> >
> > diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c
> > index 003dc1dc2da3..f7bc914a74df 100644
> > --- a/fs/ext4/block_validity.c
> > +++ b/fs/ext4/block_validity.c
> > @@ -330,11 +330,13 @@ void ext4_release_system_zone(struct super_block *sb)
> > {
> > struct ext4_system_blocks *system_blks;
> >
> > + rcu_read_lock();
> > system_blks = rcu_dereference(EXT4_SB(sb)->system_blks);
> > rcu_assign_pointer(EXT4_SB(sb)->system_blks, NULL);
> >
> > if (system_blks)
> > call_rcu(&system_blks->rcu, ext4_destroy_system_zone);
> > + rcu_read_unlock();
> > }
> >
> > int ext4_data_block_valid(struct ext4_sb_info *sbi, ext4_fsblk_t start_blk,
> >
>
> Hi Ted，
> Sorry about missing this warning, I think switch to use:
> system_blks = rcu_dereference_raw(EXT4_SB(sb)->system_blks);
> or
> system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks, true);
> is enough to fix this waring, am I missing something?
Proper fix for this is actually using:
system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks,
lockdep_is_held(&sb->s_umount));
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2019-08-26 15:03 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-15 11:47 [PATCH v5] ext4: fix potential use after free in system zone via remount with noblock_validity zhangyi (F)
2019-08-25 3:40 ` Theodore Y. Ts'o
2019-08-25 17:32 ` Eric Biggers
2019-08-26 2:56 ` Theodore Y. Ts'o
2019-08-26 8:31 ` zhangyi (F)
2019-08-26 15:03 ` Jan Kara [this message]
2019-08-27 9:20 ` zhangyi (F)
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