Re: [PATCH] pstore: Fix uaf when backend is unregistered

[Zach Wade <zachwade.k@gmail.com>]

On 2024/10/9 21:36, Zach Wade wrote:
> 
> 
> On 2024/10/9 1:23, Kees Cook wrote:
>> On Wed, Oct 09, 2024 at 01:10:14AM +0800, Zach Wade wrote:
>>> when unload pstore_blk, we will unlink the pstore file and
>>> set pos->dentry to NULL, but simple_unlink(d_inode(root), pos->dentry)
>>> may free inode of pos->dentry and free pos by free_pstore_private,
>>> this may trigger uaf. kasan report:
>>
>> Thanks for this! I need to double check what happening here a bit more
>> closely, as maybe some ordering changed after a43e0fc5e913 ("pstore:
>> inode: Only d_invalidate() is needed")
>>
>>> @@ -316,9 +316,10 @@ int pstore_put_backend_records(struct 
>>> pstore_info *psi)
>>>           list_for_each_entry_safe(pos, tmp, &records_list, list) {
>>>               if (pos->record->psi == psi) {
>>>                   list_del_init(&pos->list);
>>> -                d_invalidate(pos->dentry);
>>> -                simple_unlink(d_inode(root), pos->dentry);
>>> +                unlink_dentry = pos->dentry;
>>>                   pos->dentry = NULL;
>>> +                d_invalidate(unlink_dentry);
>>> +                simple_unlink(d_inode(root), unlink_dentry);
>>
>> But on the face of it, this does solve the UAF. I'll double-check that
>> this isn't a result of the mentioned commit.
> 
> Hi Cook,
> 
> However, I think a more appropriate solution to the problem here is to
> check the reference count when uninstalling the mount point.
> 
> At the same time, the test script is attached:
> #!/bin/bash
> modprobe pstore_blk
> blkdev=/dev/sda2
> best_effort=on
> mount -t pstore pstore /sys/fs/pstore
> sleep 2
> umount /sys/fs/pstore
> modprobe -r pstore_blk
> 
> Thanks,
> Zach
> 
>>
> 
>> -Kees
>>
> 

friendly ping.

Hi Cook,

How are you doing? I really hope we can solve this problem.

Thanks,
Zach