[PATCH] fs: fuse: dax: set fc->dax to NULL in fuse_dax_conn_free()

[PATCH] fs: fuse: dax: set fc->dax to NULL in fuse_dax_conn_free()

[Hangyu Hua]

fuse_dax_conn_free() will be called when fuse_fill_super_common() fails
after fuse_dax_conn_alloc(). Then deactivate_locked_super() in
virtio_fs_get_tree() will call virtio_kill_sb() to release the discarded
superblock. This will call fuse_dax_conn_free() again in fuse_conn_put(),
resulting in a possible double free.

Fixes: 1dd539577c42 ("virtiofs: add a mount option to enable dax")
Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
---
 fs/fuse/dax.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
index 23904a6a9a96..12ef91d170bb 100644
--- a/fs/fuse/dax.c
+++ b/fs/fuse/dax.c
@@ -1222,6 +1222,7 @@ void fuse_dax_conn_free(struct fuse_conn *fc)
 	if (fc->dax) {
 		fuse_free_dax_mem_ranges(&fc->dax->free_ranges);
 		kfree(fc->dax);
+		fc->dax = NULL;
 	}
 }
 
-- 
2.34.1

Re: [PATCH] fs: fuse: dax: set fc->dax to NULL in fuse_dax_conn_free()

[Jingbo Xu]

On 11/16/23 3:57 PM, Hangyu Hua wrote:
> fuse_dax_conn_free() will be called when fuse_fill_super_common() fails
> after fuse_dax_conn_alloc(). Then deactivate_locked_super() in
> virtio_fs_get_tree() will call virtio_kill_sb() to release the discarded
> superblock. This will call fuse_dax_conn_free() again in fuse_conn_put(),
> resulting in a possible double free.
> 
> Fixes: 1dd539577c42 ("virtiofs: add a mount option to enable dax")
> Signed-off-by: Hangyu Hua <hbh25y@gmail.com>

Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>

> ---
>  fs/fuse/dax.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
> index 23904a6a9a96..12ef91d170bb 100644
> --- a/fs/fuse/dax.c
> +++ b/fs/fuse/dax.c
> @@ -1222,6 +1222,7 @@ void fuse_dax_conn_free(struct fuse_conn *fc)
>  	if (fc->dax) {
>  		fuse_free_dax_mem_ranges(&fc->dax->free_ranges);
>  		kfree(fc->dax);
> +		fc->dax = NULL;
>  	}
>  }
>  

-- 
Thanks,
Jingbo

Re: [PATCH] fs: fuse: dax: set fc->dax to NULL in fuse_dax_conn_free()

[Miklos Szeredi]

On Thu, 16 Nov 2023 at 08:57, Hangyu Hua <hbh25y@gmail.com> wrote:
>
> fuse_dax_conn_free() will be called when fuse_fill_super_common() fails
> after fuse_dax_conn_alloc(). Then deactivate_locked_super() in
> virtio_fs_get_tree() will call virtio_kill_sb() to release the discarded
> superblock. This will call fuse_dax_conn_free() again in fuse_conn_put(),
> resulting in a possible double free.
>
> Fixes: 1dd539577c42 ("virtiofs: add a mount option to enable dax")
> Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
> ---
>  fs/fuse/dax.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
> index 23904a6a9a96..12ef91d170bb 100644
> --- a/fs/fuse/dax.c
> +++ b/fs/fuse/dax.c
> @@ -1222,6 +1222,7 @@ void fuse_dax_conn_free(struct fuse_conn *fc)
>         if (fc->dax) {
>                 fuse_free_dax_mem_ranges(&fc->dax->free_ranges);
>                 kfree(fc->dax);
> +               fc->dax = NULL;

Is there a reason not to simply remove the fuse_dax_conn_free() call
from the cleanup path in fuse_fill_super_common()?

Thanks,
Miklos


>         }
>  }
>
> --
> 2.34.1
>

Re: [PATCH] fs: fuse: dax: set fc->dax to NULL in fuse_dax_conn_free()

[Hangyu Hua]

On 30/11/2023 18:54, Miklos Szeredi wrote:
> On Thu, 16 Nov 2023 at 08:57, Hangyu Hua <hbh25y@gmail.com> wrote:
>>
>> fuse_dax_conn_free() will be called when fuse_fill_super_common() fails
>> after fuse_dax_conn_alloc(). Then deactivate_locked_super() in
>> virtio_fs_get_tree() will call virtio_kill_sb() to release the discarded
>> superblock. This will call fuse_dax_conn_free() again in fuse_conn_put(),
>> resulting in a possible double free.
>>
>> Fixes: 1dd539577c42 ("virtiofs: add a mount option to enable dax")
>> Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
>> ---
>>   fs/fuse/dax.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
>> index 23904a6a9a96..12ef91d170bb 100644
>> --- a/fs/fuse/dax.c
>> +++ b/fs/fuse/dax.c
>> @@ -1222,6 +1222,7 @@ void fuse_dax_conn_free(struct fuse_conn *fc)
>>          if (fc->dax) {
>>                  fuse_free_dax_mem_ranges(&fc->dax->free_ranges);
>>                  kfree(fc->dax);
>> +               fc->dax = NULL;
> 
> Is there a reason not to simply remove the fuse_dax_conn_free() call
> from the cleanup path in fuse_fill_super_common()?

I think setting fc->dax to NULL keeps the memory allocation and release 
functions together in fuse_fill_super_common more readable. What do you 
think?

Thanks,
Hangyu

> 
> Thanks,
> Miklos
> 
> 
>>          }
>>   }
>>
>> --
>> 2.34.1
>>

Re: [PATCH] fs: fuse: dax: set fc->dax to NULL in fuse_dax_conn_free()

[Vivek Goyal]

On Fri, Dec 01, 2023 at 10:42:53AM +0800, Hangyu Hua wrote:
> On 30/11/2023 18:54, Miklos Szeredi wrote:
> > On Thu, 16 Nov 2023 at 08:57, Hangyu Hua <hbh25y@gmail.com> wrote:
> > > 
> > > fuse_dax_conn_free() will be called when fuse_fill_super_common() fails
> > > after fuse_dax_conn_alloc(). Then deactivate_locked_super() in
> > > virtio_fs_get_tree() will call virtio_kill_sb() to release the discarded
> > > superblock. This will call fuse_dax_conn_free() again in fuse_conn_put(),
> > > resulting in a possible double free.
> > > 
> > > Fixes: 1dd539577c42 ("virtiofs: add a mount option to enable dax")
> > > Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
> > > ---
> > >   fs/fuse/dax.c | 1 +
> > >   1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
> > > index 23904a6a9a96..12ef91d170bb 100644
> > > --- a/fs/fuse/dax.c
> > > +++ b/fs/fuse/dax.c
> > > @@ -1222,6 +1222,7 @@ void fuse_dax_conn_free(struct fuse_conn *fc)
> > >          if (fc->dax) {
> > >                  fuse_free_dax_mem_ranges(&fc->dax->free_ranges);
> > >                  kfree(fc->dax);
> > > +               fc->dax = NULL;
> > 
> > Is there a reason not to simply remove the fuse_dax_conn_free() call
> > from the cleanup path in fuse_fill_super_common()?
> 
> I think setting fc->dax to NULL keeps the memory allocation and release
> functions together in fuse_fill_super_common more readable. What do you
> think?

I agree with this. fuse_fill_super_common() calls fuse_dax_conn_alloc()
which in-turn initializes fc->dax. If fuse_fill_super_common() fails
later after calling fuse_dax_conn_alloc(), then cleanup of fc->dax
and other associated stuff in same function makes sense.

As a code reader I would like to know how fc->dax is being freed in
case of error and its right there in the error path (err_free_dax:).

I think I set the fc->dax upon initialization. Upon failure I freed
the data structures but did not set fc->dax back to NULL.

To me, this patch looks reasonable.

Acked-by: Vivek Goyal <vgoyal@redhat.com>

Thanks
Vivek

> 
> Thanks,
> Hangyu
> 
> > 
> > Thanks,
> > Miklos
> > 
> > 
> > >          }
> > >   }
> > > 
> > > --
> > > 2.34.1
> > > 
> 

Re: [PATCH] fs: fuse: dax: set fc->dax to NULL in fuse_dax_conn_free()

[Miklos Szeredi]

On Fri, 1 Dec 2023 at 20:08, Vivek Goyal <vgoyal@redhat.com> wrote:
>
> On Fri, Dec 01, 2023 at 10:42:53AM +0800, Hangyu Hua wrote:

> > I think setting fc->dax to NULL keeps the memory allocation and release
> > functions together in fuse_fill_super_common more readable. What do you
> > think?
>
> I agree with this. fuse_fill_super_common() calls fuse_dax_conn_alloc()
> which in-turn initializes fc->dax. If fuse_fill_super_common() fails
> later after calling fuse_dax_conn_alloc(), then cleanup of fc->dax
> and other associated stuff in same function makes sense.
>
> As a code reader I would like to know how fc->dax is being freed in
> case of error and its right there in the error path (err_free_dax:).
>
> I think I set the fc->dax upon initialization. Upon failure I freed
> the data structures but did not set fc->dax back to NULL.
>
> To me, this patch looks reasonable.
>
> Acked-by: Vivek Goyal <vgoyal@redhat.com>

Applied, thanks.

The patch is clearly correct, so I have not major issue with it.   It
just bothers me a little that we have two cleanup instances when we
only need one, but I bow to the opinion of the majority.

Thanks,
Miklos