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

Jan Kara
2022-11-02T12:47:46Z

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