Re: [PATCH] ext4: fix use-after-free in ext4_orphan_cleanup

[Jan Kara <jack@suse.cz>]

On Wed 02-11-22 16:06:33, Baokun Li wrote:
> I caught a issue as follows:
> ==================================================================
>  BUG: KASAN: use-after-free in __list_add_valid+0x28/0x1a0
>  Read of size 8 at addr ffff88814b13f378 by task mount/710
> 
>  CPU: 1 PID: 710 Comm: mount Not tainted 6.1.0-rc3-next #370
>  Call Trace:
>   <TASK>
>   dump_stack_lvl+0x73/0x9f
>   print_report+0x25d/0x759
>   kasan_report+0xc0/0x120
>   __asan_load8+0x99/0x140
>   __list_add_valid+0x28/0x1a0
>   ext4_orphan_cleanup+0x564/0x9d0 [ext4]
>   __ext4_fill_super+0x48e2/0x5300 [ext4]
>   ext4_fill_super+0x19f/0x3a0 [ext4]
>   get_tree_bdev+0x27b/0x450
>   ext4_get_tree+0x19/0x30 [ext4]
>   vfs_get_tree+0x49/0x150
>   path_mount+0xaae/0x1350
>   do_mount+0xe2/0x110
>   __x64_sys_mount+0xf0/0x190
>   do_syscall_64+0x35/0x80
>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
>   </TASK>
>  [...]
> ==================================================================
> 
> Above issue may happen as follows:
> -------------------------------------
> ext4_fill_super
>   ext4_orphan_cleanup
>    --- loop1: assume last_orphan is 12 ---
>     list_add(&EXT4_I(inode)->i_orphan, &EXT4_SB(sb)->s_orphan)
>     ext4_truncate --> return 0
>       ext4_inode_attach_jinode --> return -ENOMEM
>     iput(inode) --> free inode<12>
>    --- loop2: last_orphan is still 12 ---
>     list_add(&EXT4_I(inode)->i_orphan, &EXT4_SB(sb)->s_orphan);
>     // use inode<12> and trigger UAF
> 
> To solve this issue, we need to propagate the return value of
> ext4_inode_attach_jinode() appropriately.
> 
> Signed-off-by: Baokun Li <libaokun1@huawei.com>

Nice catch. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>
	
								Honza

> ---
>  fs/ext4/inode.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index fca47470c85a..e7e7561f0baa 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4224,7 +4224,8 @@ int ext4_truncate(struct inode *inode)
>  
>  	/* If we zero-out tail of the page, we have to create jinode for jbd2 */
>  	if (inode->i_size & (inode->i_sb->s_blocksize - 1)) {
> -		if (ext4_inode_attach_jinode(inode) < 0)
> +		err = ext4_inode_attach_jinode(inode);
> +		if (err)
>  			goto out_trace;
>  	}
>  
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR