linux-kernel - Re: [PATCH] ceph: fix memory leak in mount error path when using test_dummy

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Date:   Mon, 7 Nov 2022 10:23:41 +0000
From:   Luís Henriques <lhenriques@...e.de>
To:     Xiubo Li <xiubli@...hat.com>
Cc:     Ilya Dryomov <idryomov@...il.com>,
        Jeff Layton <jlayton@...nel.org>, ceph-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ceph: fix memory leak in mount error path when using
 test_dummy_encryption

On Mon, Nov 07, 2022 at 03:47:23PM +0800, Xiubo Li wrote:
> 
> On 03/11/2022 23:36, Luís Henriques wrote:
> > Because ceph_init_fs_context() will never be invoced in case we get a
> > mount error, destroy_mount_options() won't be releasing fscrypt resources
> > with fscrypt_free_dummy_policy().  This will result in a memory leak.  Add
> > an invocation to this function in the mount error path.
> > 
> > Signed-off-by: Luís Henriques <lhenriques@...e.de>
> > ---
> >   fs/ceph/super.c | 1 +
> >   1 file changed, 1 insertion(+)
> > 
> > diff --git a/fs/ceph/super.c b/fs/ceph/super.c
> > index 2224d44d21c0..6b9fd04b25cd 100644
> > --- a/fs/ceph/super.c
> > +++ b/fs/ceph/super.c
> > @@ -1362,6 +1362,7 @@ static int ceph_get_tree(struct fs_context *fc)
> >   	ceph_mdsc_close_sessions(fsc->mdsc);
> >   	deactivate_locked_super(sb);
> > +	fscrypt_free_dummy_policy(&fsc->fsc_dummy_enc_policy);
> 
> Hi Luis,
> 
> BTW, any reason the following code won't be triggered ?
> 
> deactivate_locked_super(sb);
> 
>   --> fs->kill_sb(s);
> 
>         --> ceph_kill_sb()
> 
>               --> kill_anon_super()
> 
>                     --> generic_shutdown_super()
> 
>                           --> sop->put_super()
> 
>                                 --> ceph_put_super()
> 
>                                       --> ceph_fscrypt_free_dummy_policy()
> 
>                                            --> fscrypt_free_dummy_policy(
> 

Here's what I'm seeing here:

  sys_mount->path_mount->do_new_mount->vfs_get_tree->ceph_get_tree

ceph_get_tree() fails due to ceph_real_mount() returning an error.  My
understanding is that that, since fc->root is never set, that code path
will never be triggered.  Does that make sense?

An easy way to reproduce is by running fstest ceph/005 with the
'test_dummy_encryption' option.  (I'll probably need to send a patch to
disable this test when this option is present.)

Cheers,
--
Luís