ocfs2: fix use-after-free when unmounting read-only filesystem

  It's trivial to trigger a use-after-free bug in the ocfs2 quotas code using
fstest generic/452.  After mounting a filesystem as read-only, quotas are
suspended and ocfs2_mem_dqinfo is freed through ->ocfs2_local_free_info().  When
unmounting the filesystem, an UAF access to the oinfo will eventually cause a
crash.

Cc: <stable@vger.kernel.org>
Signed-off-by: Luís Henriques <lhenriques@suse.de>
---
 fs/ocfs2/super.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
  

On 5/22/23 6:25 PM, Luís Henriques wrote:
> It's trivial to trigger a use-after-free bug in the ocfs2 quotas code using
> fstest generic/452.  After mounting a filesystem as read-only, quotas are

generic/452 is for testing ext4 mounted with dax and ro.
But ocfs2 doesn't support dax yet. 

> suspended and ocfs2_mem_dqinfo is freed through ->ocfs2_local_free_info().  When
> unmounting the filesystem, an UAF access to the oinfo will eventually cause a
> crash.

In ocfs2_fill_super(), it won't enable quota if is a readonly mount.
Do you mean remount as readonly?

Thanks,
Joseph

> 
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Luís Henriques <lhenriques@suse.de>
> ---
>  fs/ocfs2/super.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
> index 0b0e6a132101..988d1c076861 100644
> --- a/fs/ocfs2/super.c
> +++ b/fs/ocfs2/super.c
> @@ -952,8 +952,10 @@ static void ocfs2_disable_quotas(struct ocfs2_super *osb)
>  	for (type = 0; type < OCFS2_MAXQUOTAS; type++) {
>  		if (!sb_has_quota_loaded(sb, type))
>  			continue;
> -		oinfo = sb_dqinfo(sb, type)->dqi_priv;
> -		cancel_delayed_work_sync(&oinfo->dqi_sync_work);
> +		if (!sb_has_quota_suspended(sb, type)) {
> +			oinfo = sb_dqinfo(sb, type)->dqi_priv;
> +			cancel_delayed_work_sync(&oinfo->dqi_sync_work);
> +		}
>  		inode = igrab(sb->s_dquot.files[type]);
>  		/* Turn off quotas. This will remove all dquot structures from
>  		 * memory and so they will be automatically synced to global
  

Joseph Qi <joseph.qi@linux.alibaba.com> writes:

> On 5/22/23 6:25 PM, Luís Henriques wrote:
>> It's trivial to trigger a use-after-free bug in the ocfs2 quotas code using
>> fstest generic/452.  After mounting a filesystem as read-only, quotas are
>
> generic/452 is for testing ext4 mounted with dax and ro.
> But ocfs2 doesn't support dax yet.

Right, but I think it's still useful to run the 'generic' test-suite in a
filesystem.  We can always find issues in the test itself or, in this
case, a bug in the filesystem.

>> suspended and ocfs2_mem_dqinfo is freed through ->ocfs2_local_free_info().  When
>> unmounting the filesystem, an UAF access to the oinfo will eventually cause a
>> crash.
>
> In ocfs2_fill_super(), it won't enable quota if is a readonly mount.
> Do you mean remount as readonly?

Yes, sorry. Instead of "mounting", the patch changelog should say

  "After remounting a filesystem as read-only..."

Cheers,
  

On Mon, May 22, 2023 at 01:23:07PM +0100, Luís Henriques wrote:
> Joseph Qi <joseph.qi@linux.alibaba.com> writes:
> 
> > On 5/22/23 6:25 PM, Luís Henriques wrote:
> >> It's trivial to trigger a use-after-free bug in the ocfs2 quotas code using
> >> fstest generic/452.  After mounting a filesystem as read-only, quotas are
> >
> > generic/452 is for testing ext4 mounted with dax and ro.
> > But ocfs2 doesn't support dax yet.
> 
> Right, but I think it's still useful to run the 'generic' test-suite in a
> filesystem.  We can always find issues in the test itself or, in this
> case, a bug in the filesystem.

It looks you did some special steps for 452. In my env, without changing
anything, I could pass this case successfully. 

- Heming

> 
> >> suspended and ocfs2_mem_dqinfo is freed through ->ocfs2_local_free_info().  When
> >> unmounting the filesystem, an UAF access to the oinfo will eventually cause a
> >> crash.
> >
> > In ocfs2_fill_super(), it won't enable quota if is a readonly mount.
> > Do you mean remount as readonly?
> 
> Yes, sorry. Instead of "mounting", the patch changelog should say
> 
>   "After remounting a filesystem as read-only..."
> 
> Cheers,
> -- 
> Luís
> 
> >
> > Thanks,
> > Joseph
> >
> >> 
> >> Cc: <stable@vger.kernel.org>
> >> Signed-off-by: Luís Henriques <lhenriques@suse.de>
> >> ---
> >>  fs/ocfs2/super.c | 6 ++++--
> >>  1 file changed, 4 insertions(+), 2 deletions(-)
> >> 
> >> diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
> >> index 0b0e6a132101..988d1c076861 100644
> >> --- a/fs/ocfs2/super.c
> >> +++ b/fs/ocfs2/super.c
> >> @@ -952,8 +952,10 @@ static void ocfs2_disable_quotas(struct ocfs2_super *osb)
> >>  	for (type = 0; type < OCFS2_MAXQUOTAS; type++) {
> >>  		if (!sb_has_quota_loaded(sb, type))
> >>  			continue;
> >> -		oinfo = sb_dqinfo(sb, type)->dqi_priv;
> >> -		cancel_delayed_work_sync(&oinfo->dqi_sync_work);
> >> +		if (!sb_has_quota_suspended(sb, type)) {
> >> +			oinfo = sb_dqinfo(sb, type)->dqi_priv;
> >> +			cancel_delayed_work_sync(&oinfo->dqi_sync_work);
> >> +		}
> >>  		inode = igrab(sb->s_dquot.files[type]);
> >>  		/* Turn off quotas. This will remove all dquot structures from
> >>  		 * memory and so they will be automatically synced to global
>
  

Heming Zhao <heming.zhao@suse.com> writes:

> On Mon, May 22, 2023 at 01:23:07PM +0100, Luís Henriques wrote:
>> Joseph Qi <joseph.qi@linux.alibaba.com> writes:
>> 
>> > On 5/22/23 6:25 PM, Luís Henriques wrote:
>> >> It's trivial to trigger a use-after-free bug in the ocfs2 quotas code using
>> >> fstest generic/452.  After mounting a filesystem as read-only, quotas are
>> >
>> > generic/452 is for testing ext4 mounted with dax and ro.
>> > But ocfs2 doesn't support dax yet.
>> 
>> Right, but I think it's still useful to run the 'generic' test-suite in a
>> filesystem.  We can always find issues in the test itself or, in this
>> case, a bug in the filesystem.
>
> It looks you did some special steps for 452. In my env, without changing
> anything, I could pass this case successfully. 

No, I haven't changed anything to the test.  I just make sure there's a
scratch device to be used.

Maybe you can try to enable KASAN to catch the UAF.  I've found the bug
without KASAN (i.e. I saw a NULL pointer panic), but enabling it also
detects the issue -- see below.

Cheers,
  

On 5/22/23 8:23 PM, Luís Henriques wrote:
> Joseph Qi <joseph.qi@linux.alibaba.com> writes:
> 
>> On 5/22/23 6:25 PM, Luís Henriques wrote:
>>> It's trivial to trigger a use-after-free bug in the ocfs2 quotas code using
>>> fstest generic/452.  After mounting a filesystem as read-only, quotas are
>>
>> generic/452 is for testing ext4 mounted with dax and ro.
>> But ocfs2 doesn't support dax yet.
> 
> Right, but I think it's still useful to run the 'generic' test-suite in a
> filesystem.  We can always find issues in the test itself or, in this
> case, a bug in the filesystem.
> 
>>> suspended and ocfs2_mem_dqinfo is freed through ->ocfs2_local_free_info().  When
>>> unmounting the filesystem, an UAF access to the oinfo will eventually cause a
>>> crash.
>>
>> In ocfs2_fill_super(), it won't enable quota if is a readonly mount.
>> Do you mean remount as readonly?
> 
> Yes, sorry. Instead of "mounting", the patch changelog should say
> 
>   "After remounting a filesystem as read-only..."
> 
> Cheers,

Okay, look into the code flow, it does have problem when remount with
read-only.
BTW, it seems that we can't call into quota_disable() again, which will
call free_file_info().

Thanks,
Joseph
  

On 5/22/23 9:22 PM, Luís Henriques wrote:
> Heming Zhao <heming.zhao@suse.com> writes:
> 
>> On Mon, May 22, 2023 at 01:23:07PM +0100, Luís Henriques wrote:
>>> Joseph Qi <joseph.qi@linux.alibaba.com> writes:
>>>
>>>> On 5/22/23 6:25 PM, Luís Henriques wrote:
>>>>> It's trivial to trigger a use-after-free bug in the ocfs2 quotas code using
>>>>> fstest generic/452.  After mounting a filesystem as read-only, quotas are
>>>>
>>>> generic/452 is for testing ext4 mounted with dax and ro.
>>>> But ocfs2 doesn't support dax yet.
>>>
>>> Right, but I think it's still useful to run the 'generic' test-suite in a
>>> filesystem.  We can always find issues in the test itself or, in this
>>> case, a bug in the filesystem.
>>
>> It looks you did some special steps for 452. In my env, without changing
>> anything, I could pass this case successfully. 
> 
> No, I haven't changed anything to the test.  I just make sure there's a
> scratch device to be used.
> 
> Maybe you can try to enable KASAN to catch the UAF.  I've found the bug
> without KASAN (i.e. I saw a NULL pointer panic), but enabling it also
> detects the issue -- see below.
> 
> Cheers,

We'd better append panic dmesg to patch description as well.

Thanks,
Joseph