Re: [PATCH 1/2] block: Fix Transaction leak in bdrv_root_attach_child()

[Max Reitz]

On 03.05.21 13:51, Vladimir Sementsov-Ogievskiy wrote:
> 03.05.2021 14:49, Max Reitz wrote:
> > On 03.05.21 13:05, Kevin Wolf wrote:
> > > The error path needs to call tran_finalize(), too.
> > >
> > > Fixes: CID 1452773
> > > Fixes: 548a74c0dbc858edd1a7ee3045b5f2fe710bd8b1
> > > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > > ---
> > >   block.c | 7 ++++---
> > >   1 file changed, 4 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/block.c b/block.c
> > > index 874c22c43e..5c0ced6238 100644
> > > --- a/block.c
> > > +++ b/block.c
> > > @@ -2918,13 +2918,14 @@ BdrvChild 
> > > *bdrv_root_attach_child(BlockDriverState *child_bs,
> > >                                      child_role, perm, shared_perm, 
> > > opaque,
> > >                                      &child, tran, errp);
> > >       if (ret < 0) {
> > > -        bdrv_unref(child_bs);
> > > -        return NULL;
> > > +        assert(child == NULL);
> > > +        goto out;
> > >       }
> > >       ret = bdrv_refresh_perms(child_bs, errp);
> > > -    tran_finalize(tran, ret);
> > > +out:
> > > +    tran_finalize(tran, ret);
> > >       bdrv_unref(child_bs);
> > >       return child;
> >
> > Looks OK, so:
> >
> > Reviewed-by: Max Reitz <mreitz@redhat.com>
> >
> > However, the function’s description says that it will return NULL on 
> > error.  But if bdrv_refresh_perms() fails, it will still return a 
> > non-NULL child.  Is that right?
>
> No, it's reset to NULL on transaction abort, so code is correct. It's 
> not obvious, and I've added a comment and assertion in my version of 
> this fix "[PATCH 1/6] block: fix leak of tran in bdrv_root_attach_child"

The fact that the transaction keeps the pointer to this local variable 
around is a bit horrifying, but well.

Max