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Message-ID: <20230530095726.t2grmww5rzofx5gp@quack3>
Date: Tue, 30 May 2023 11:57:26 +0200
From: Jan Kara <jack@...e.cz>
To: Ye Bin <yebin10@...wei.com>
Cc: jack@...e.com, linux-kernel@...r.kernel.org,
syzbot+e633c79ceaecbf479854@...kaller.appspotmail.com
Subject: Re: [PATCH 1/2] quota: fix null-ptr-deref in ext4_acquire_dquot()
On Sat 27-05-23 09:40:17, Ye Bin wrote:
> Syzbot found the following issue:
> Unable to handle kernel paging request at virtual address dfff800000000005
> KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
...
> CPU: 0 PID: 6080 Comm: syz-executor747 Not tainted 6.3.0-rc7-syzkaller-g14f8db1c0f9a #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/14/2023
> pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> pc : ext4_acquire_dquot+0x1d4/0x398 fs/ext4/super.c:6766
> lr : dquot_to_inode fs/ext4/super.c:6740 [inline]
> lr : ext4_acquire_dquot+0x1ac/0x398 fs/ext4/super.c:6766
OK, this is bad...
> Above issue may happens as follows:
> ProcessA ProcessB ProcessC
> sys_fsconfig
> vfs_fsconfig_locked
> reconfigure_super
> ext4_remount
> dquot_suspend -> suspend all type quota
>
> sys_fsconfig
> vfs_fsconfig_locked
> reconfigure_super
> ext4_remount
> dquot_resume
> ret = dquot_load_quota_sb
> add_dquot_ref
> do_open -> open file O_RDWR
> vfs_open
> do_dentry_open
> get_write_access
> atomic_inc_unless_negative(&inode->i_writecount)
> ext4_file_open
> dquot_file_open
> dquot_initialize
> __dquot_initialize
> dqget
> if (!test_bit(DQ_ACTIVE_B, &dquot->dq_flags))
>
> __dquot_initialize
> __dquot_initialize
> dqget
> if (!test_bit(DQ_ACTIVE_B, &dquot->dq_flags))
> ext4_acquire_dquot -> Return error
> if (ret < 0)
> vfs_cleanup_quota_inode
> dqopt->files[type] = NULL;
But I don't see how this can happen. The code in dquot_load_quota_sb()
looks like:
error = add_dquot_ref(sb, type);
if (error)
dquot_disable(sb, type, flags);
So if an error happens in add_dquot_ref(), we'll call dquot_disable().
dquot_disable() then does:
drop_dquot_ref(sb, cnt);
invalidate_dquots(sb, cnt);
and invalidate_dquots() waits for reference count of all dquots to drop to
0. Hence if dqget() returned a dquot pointer to ProcessC, then ProcessB
should wait until ProcessC drops the dquot reference (hence
ext4_acquire_dquot() is done).
What am I missing?
Honza
>
> ext4_acquire_dquot
> -->dquot_to_inode(dquot) is NULL
>
> To solve above issue, if quota has been loaded, there's unneed to cleaup quota
> inode if dquot_load_quota_sb() return failed when do dquot_resume();
>
> Reported-by: syzbot+e633c79ceaecbf479854@...kaller.appspotmail.com
> Signed-off-by: Ye Bin <yebin10@...wei.com>
> ---
> fs/quota/dquot.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
> index ffd40dc3e4e9..4b913faa48ec 100644
> --- a/fs/quota/dquot.c
> +++ b/fs/quota/dquot.c
> @@ -2476,7 +2476,7 @@ int dquot_resume(struct super_block *sb, int type)
> flags = dquot_generic_flag(flags, cnt);
> ret = dquot_load_quota_sb(sb, cnt, dqopt->info[cnt].dqi_fmt_id,
> flags);
> - if (ret < 0)
> + if (ret < 0 && !sb_has_quota_loaded(sb, cnt))
> vfs_cleanup_quota_inode(sb, cnt);
> }
>
> --
> 2.31.1
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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