Re: [PATCH 2/3] ceph: fix use-after-free in ceph_readdir

[Xiubo Li]

On 3/5/22 2:20 AM, Jeff Layton wrote:
> On Fri, 2022-03-04 at 16:14 +0000, Luís Henriques wrote:
> > After calling ceph_mdsc_put_request() on dfi->last_readdir, this field
> > should be set to NULL, otherwise we may end-up freeing it twince and get
> > the following splat:
> >
> >    refcount_t: underflow; use-after-free.
> >    WARNING: CPU: 0 PID: 229 at lib/refcount.c:28 refcount_warn_saturate+0xa6/0xf0
> >    ...
> >    Call Trace:
> >      <TASK>
> >      ceph_readdir+0xd35/0x1460 [ceph]
> >      ? _raw_spin_unlock+0x12/0x30
> >      ? preempt_count_add+0x73/0xa0
> >      ? _raw_spin_unlock+0x12/0x30
> >      ? __mark_inode_dirty+0x27c/0x3a0
> >      iterate_dir+0x7d/0x190
> >      __x64_sys_getdents64+0x80/0x120
> >      ? compat_fillonedir+0x160/0x160
> >      do_syscall_64+0x43/0x90
> >      entry_SYSCALL_64_after_hwframe+0x44/0xae
> >
> > Signed-off-by: Luís Henriques <lhenriques@xxxxxxx>
> > ---
> >   fs/ceph/dir.c | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
> > index 0bcb677d2199..934402f5e9e6 100644
> > --- a/fs/ceph/dir.c
> > +++ b/fs/ceph/dir.c
> > @@ -555,6 +555,7 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
> >   			      le32_to_cpu(rde->inode.in->mode) >> 12)) {
> >   			dout("filldir stopping us...\n");
> >   			ceph_mdsc_put_request(dfi->last_readdir);
> > +			dfi->last_readdir = NULL;
> >   			err = 0;
> >   			goto out;
> >   		}
> I think Xiubo fixed this in the testing branch late yesterday. It should
> no longer be needed.

Right and I have sent a new version of my previous patch to remove the 
buggy code.

- Xiubo

> Thanks,