From: Jan Kara <jack@suse.cz>
To: Baokun Li <libaokun1@huawei.com>
Cc: Lukas Czerner <lczerner@redhat.com>,
linux-ext4@vger.kernel.org, tytso@mit.edu,
adilger.kernel@dilger.ca, jack@suse.cz, ritesh.list@gmail.com,
enwlinux@gmail.com, linux-kernel@vger.kernel.org,
yi.zhang@huawei.com, yebin10@huawei.com, yukuai3@huawei.com
Subject: Re: [PATCH] ext4: fix null-ptr-deref in ext4_write_info
Date: Mon, 15 Aug 2022 17:34:10 +0200 [thread overview]
Message-ID: <20220815153410.vupcecnlmcjr4fmg@quack3> (raw)
In-Reply-To: <c937578b-e7f2-79cb-2e81-3330edf2bf6c@huawei.com>
On Wed 10-08-22 15:20:48, Baokun Li wrote:
> 在 2022/8/5 21:07, Lukas Czerner 写道:
> > On Fri, Aug 05, 2022 at 08:39:47PM +0800, Baokun Li wrote:
> > > I caught a null-ptr-deref bug as follows:
> > > ==================================================================
> > > KASAN: null-ptr-deref in range [0x0000000000000068-0x000000000000006f]
> > > CPU: 1 PID: 1589 Comm: umount Not tainted 5.10.0-02219-dirty #339
> > > RIP: 0010:ext4_write_info+0x53/0x1b0
> > > [...]
> > > Call Trace:
> > > dquot_writeback_dquots+0x341/0x9a0
> > > ext4_sync_fs+0x19e/0x800
> > > __sync_filesystem+0x83/0x100
> > > sync_filesystem+0x89/0xf0
> > > generic_shutdown_super+0x79/0x3e0
> > > kill_block_super+0xa1/0x110
> > > deactivate_locked_super+0xac/0x130
> > > deactivate_super+0xb6/0xd0
> > > cleanup_mnt+0x289/0x400
> > > __cleanup_mnt+0x16/0x20
> > > task_work_run+0x11c/0x1c0
> > > exit_to_user_mode_prepare+0x203/0x210
> > > syscall_exit_to_user_mode+0x5b/0x3a0
> > > do_syscall_64+0x59/0x70
> > > entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > > ==================================================================
> > >
> > > Above issue may happen as follows:
> > > -------------------------------------
> > > exit_to_user_mode_prepare
> > > task_work_run
> > > __cleanup_mnt
> > > cleanup_mnt
> > > deactivate_super
> > > deactivate_locked_super
> > > kill_block_super
> > > generic_shutdown_super
> > > shrink_dcache_for_umount
> > > dentry = sb->s_root
> > > sb->s_root = NULL <--- Here set NULL
> > > sync_filesystem
> > > __sync_filesystem
> > > sb->s_op->sync_fs > ext4_sync_fs
> > > dquot_writeback_dquots
> > > sb->dq_op->write_info > ext4_write_info
> > > ext4_journal_start(d_inode(sb->s_root), EXT4_HT_QUOTA, 2)
> > > d_inode(sb->s_root)
> > > s_root->d_inode <--- Null pointer dereference
> > >
> > > To solve this problem, we use ext4_journal_start_sb directly
> > > to avoid s_root being used.
> > Are we syncing the file system after the superblock shutdown and getting
> > away with it? This does not look good. Do you have a reproducer?
> >
> > Thanks!
> > -Lukas
>
> Hi, Lukas!
>
> This problem is triggered by a pressure test when I reproduce another
> problem.
>
> So I didn't have the reproducer.
>
> I looked at the error stack code and found that it seems there is something
> wrong.
>
> Moreover, it's really weird to write code like
> "ext4_journal_start(d_inode(sb->s_root), ...)".
I agree. That looks like some leftover from the past. Feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
>
> > > Signed-off-by: Baokun Li <libaokun1@huawei.com>
> > > ---
> > > fs/ext4/super.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > > index 9a66abcca1a8..0ce4565422f6 100644
> > > --- a/fs/ext4/super.c
> > > +++ b/fs/ext4/super.c
> > > @@ -6653,7 +6653,7 @@ static int ext4_write_info(struct super_block *sb, int type)
> > > handle_t *handle;
> > > /* Data block + inode block */
> > > - handle = ext4_journal_start(d_inode(sb->s_root), EXT4_HT_QUOTA, 2);
> > > + handle = ext4_journal_start_sb(sb, EXT4_HT_QUOTA, 2);
> > > if (IS_ERR(handle))
> > > return PTR_ERR(handle);
> > > ret = dquot_commit_info(sb, type);
> > > --
> > > 2.31.1
> > >
> > .
>
>
> Thanks!
>
> --
> With Best Regards,
> Baokun Li
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2022-08-15 15:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-05 12:39 [PATCH] ext4: fix null-ptr-deref in ext4_write_info Baokun Li
2022-08-05 13:07 ` Lukas Czerner
2022-08-10 7:20 ` Baokun Li
2022-08-15 15:34 ` Jan Kara [this message]
2022-09-27 21:53 ` Theodore Ts'o
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