Re: [PATCH v2] ext4: don't remove reserved inodes in ext4_unlink()

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Sun, Oct 12, 2014 at 04:50:58PM +0800, Eryu Guan wrote:
> Corrupted ext4_dir_entry_2 struct on disk may have wrong inode number,
> when the inode number is 8 (EXT4_JOURNAL_INO) and the file is deleted,
> the journal inode is gone, and unmounting such a fs could trigger the
> following BUG_ON() in start_this_handle().
> 
> 	BUG_ON(journal->j_flags & JBD2_UNMOUNT);
> 
> 	------------[ cut here ]------------
> 	kernel BUG at fs/jbd2/transaction.c:307!
> 	...
> 	CPU: 1 PID: 1535 Comm: umount Not tainted 3.13.0+ #14
> 	...
> 	Call Trace:
> 	 [<ffffffff8119f17a>] ? kmem_cache_alloc+0x1ca/0x1f0
> 	 [<ffffffff812850f0>] ? jbd2__journal_start+0x90/0x1e0
> 	 [<ffffffff81285153>] jbd2__journal_start+0xf3/0x1e0
> 	 [<ffffffff81242a62>] ? ext4_evict_inode+0x1b2/0x4f0
> 	 [<ffffffff8126d039>] __ext4_journal_start_sb+0x69/0xe0
> 	 [<ffffffff81242a62>] ext4_evict_inode+0x1b2/0x4f0
> 	 [<ffffffff811d3b8e>] evict+0x9e/0x190
> 	 [<ffffffff811d4373>] iput+0xf3/0x180
> 	 [<ffffffff8128f301>] jbd2_journal_destroy+0x191/0x220
> 	 [<ffffffff810b0ae0>] ? abort_exclusive_wait+0xb0/0xb0
> 	 [<ffffffff8125d004>] ext4_put_super+0x64/0x340
> 	 [<ffffffff811bbae2>] generic_shutdown_super+0x72/0xf0
> 	 [<ffffffff811bbd77>] kill_block_super+0x27/0x70
> 	 [<ffffffff811bc05d>] deactivate_locked_super+0x3d/0x60
> 	 [<ffffffff811bc606>] deactivate_super+0x46/0x60
> 	 [<ffffffff811d7f47>] mntput_no_expire+0xa7/0x140
> 	 [<ffffffff811d939e>] SyS_umount+0x8e/0x100
> 	 [<ffffffff81690c29>] system_call_fastpath+0x16/0x1b
> 
> Check inode number in ext4_unlink() and return error if the inode number
> is reserved or nonexistent(except EXT4_ROOT_INO, as Ted pointed out that
> it's a security hole).
> 
> Tested by removing a reserved inode(modify the ondisk structure by hand)
> and unmounting the fs. Inodes 1-10 have been tested. Also tested by
> xfstests.
> 
> Signed-off-by: Eryu Guan <guaneryu@gmail.com>

Looks reasonable to me, you can add Reviewed-by if you like.

--D

> ---
> 
> (This is a v2 of an old patch, I forgot about the patch..)
> 
> v2: exempt the root inode as Ted suggested, although unlink("/") would be
> catched by vfs and unlink a corrupt file with root inode number would be
> catched by ext4_lookup, and won't reach ext4_unlink() in both cases
> 
> 	EXT4-fs error (device loop0): ext4_lookup:1441: inode #2: comm rm: 'testfile' linked to parent dir
> 	Aborting journal on device loop0-8.
> 	EXT4-fs (loop0): Remounting filesystem read-only
> 	EXT4-fs error (device loop0): ext4_lookup:1441: inode #2: comm rm: 'testfile' linked to parent dir
> 
>  fs/ext4/namei.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 603e4eb..6e6b312 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -2796,9 +2796,11 @@ end_rmdir:
>  static int ext4_unlink(struct inode *dir, struct dentry *dentry)
>  {
>  	int retval;
> +	unsigned long ino;
>  	struct inode *inode;
>  	struct buffer_head *bh;
>  	struct ext4_dir_entry_2 *de;
> +	struct super_block *sb;
>  	handle_t *handle = NULL;
>  
>  	trace_ext4_unlink_enter(dir, dentry);
> @@ -2815,13 +2817,20 @@ static int ext4_unlink(struct inode *dir, struct dentry *dentry)
>  		goto end_unlink;
>  
>  	inode = dentry->d_inode;
> +	ino = inode->i_ino;
> +	sb = dir->i_sb;
>  
>  	retval = -EIO;
> -	if (le32_to_cpu(de->inode) != inode->i_ino)
> +	if (le32_to_cpu(de->inode) != ino)
>  		goto end_unlink;
> +	if ((ino < EXT4_FIRST_INO(sb) && ino != EXT4_ROOT_INO) ||
> +	    ino > le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count)) {
> +		ext4_error(sb, "reserved or nonexistent inode %lu", ino);
> +		goto end_unlink;
> +	}
>  
>  	handle = ext4_journal_start(dir, EXT4_HT_DIR,
> -				    EXT4_DATA_TRANS_BLOCKS(dir->i_sb));
> +				    EXT4_DATA_TRANS_BLOCKS(sb));
>  	if (IS_ERR(handle)) {
>  		retval = PTR_ERR(handle);
>  		handle = NULL;
> -- 
> 1.8.3.1
> 
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