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 14:19:41 +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 07:06:40PM +0800, Xiubo Li wrote:
> 
> On 07/11/2022 18:23, Luís Henriques wrote:
> > 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?
> 
> Okay, you are right!
> 
> How about fixing it in ceph_real_mount() instead ?

Sure, I can send a patch for doing that instead.  However, my opinion is
that it makes more sense to do it, mostly because ceph_get_tree() is
already doing clean-up work on the error path (ceph_mdsc_close_sessions()
and deactivate_locked_super()).

But let me know if you really prefer doing in ceph_read_mount() and I'll
send v2.

> > 
> > 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.)
> 
> Anyway this should be fixed in kceph.

Yes, agreed.

Cheers,
--
Luís