Re: [PATCH 2/2] nfsd: clean up potential nfsd_file refcount leaks in COPY codepath

[Jeff Layton <jlayton@kernel.org>]

On Sun, 2023-01-22 at 17:10 +0000, Chuck Lever III wrote:
> 
> > On Jan 22, 2023, at 11:45 AM, Chuck Lever III <chuck.lever@oracle.com> wrote:
> > 
> > 
> > 
> > > On Jan 21, 2023, at 4:28 PM, Dai Ngo <dai.ngo@oracle.com> wrote:
> > > 
> > > 
> > > On 1/21/23 12:12 PM, Chuck Lever III wrote:
> > > > 
> > > > > On Jan 21, 2023, at 3:05 PM, Jeff Layton <jlayton@kernel.org> wrote:
> > > > > 
> > > > > On Sat, 2023-01-21 at 11:50 -0800, dai.ngo@oracle.com wrote:
> > > > > > On 1/21/23 10:56 AM, dai.ngo@oracle.com wrote:
> > > > > > > On 1/20/23 3:43 AM, Jeff Layton wrote:
> > > > > > > > On Thu, 2023-01-19 at 10:38 -0800, dai.ngo@oracle.com wrote:
> > > > > > > > > On 1/19/23 2:56 AM, Jeff Layton wrote:
> > > > > > > > > > On Wed, 2023-01-18 at 21:05 -0800, dai.ngo@oracle.com wrote:
> > > > > > > > > > > On 1/17/23 11:38 AM, Jeff Layton wrote:
> > > > > > > > > > > > There are two different flavors of the nfsd4_copy struct. One is
> > > > > > > > > > > > embedded in the compound and is used directly in synchronous
> > > > > > > > > > > > copies. The
> > > > > > > > > > > > other is dynamically allocated, refcounted and tracked in the client
> > > > > > > > > > > > struture. For the embedded one, the cleanup just involves
> > > > > > > > > > > > releasing any
> > > > > > > > > > > > nfsd_files held on its behalf. For the async one, the cleanup is
> > > > > > > > > > > > a bit
> > > > > > > > > > > > more involved, and we need to dequeue it from lists, unhash it, etc.
> > > > > > > > > > > > 
> > > > > > > > > > > > There is at least one potential refcount leak in this code now.
> > > > > > > > > > > > If the
> > > > > > > > > > > > kthread_create call fails, then both the src and dst nfsd_files
> > > > > > > > > > > > in the
> > > > > > > > > > > > original nfsd4_copy object are leaked.
> > > > > > > > > > > > 
> > > > > > > > > > > > The cleanup in this codepath is also sort of weird. In the async
> > > > > > > > > > > > copy
> > > > > > > > > > > > case, we'll have up to four nfsd_file references (src and dst for
> > > > > > > > > > > > both
> > > > > > > > > > > > flavors of copy structure). They are both put at the end of
> > > > > > > > > > > > nfsd4_do_async_copy, even though the ones held on behalf of the
> > > > > > > > > > > > embedded
> > > > > > > > > > > > one outlive that structure.
> > > > > > > > > > > > 
> > > > > > > > > > > > Change it so that we always clean up the nfsd_file refs held by the
> > > > > > > > > > > > embedded copy structure before nfsd4_copy returns. Rework
> > > > > > > > > > > > cleanup_async_copy to handle both inter and intra copies. Eliminate
> > > > > > > > > > > > nfsd4_cleanup_intra_ssc since it now becomes a no-op.
> > > > > > > > > > > > 
> > > > > > > > > > > > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > > > > > > > > > > > ---
> > > > > > > > > > > >    fs/nfsd/nfs4proc.c | 23 ++++++++++-------------
> > > > > > > > > > > >    1 file changed, 10 insertions(+), 13 deletions(-)
> > > > > > > > > > > > 
> > > > > > > > > > > > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> > > > > > > > > > > > index 37a9cc8ae7ae..62b9d6c1b18b 100644
> > > > > > > > > > > > --- a/fs/nfsd/nfs4proc.c
> > > > > > > > > > > > +++ b/fs/nfsd/nfs4proc.c
> > > > > > > > > > > > @@ -1512,7 +1512,6 @@ nfsd4_cleanup_inter_ssc(struct
> > > > > > > > > > > > nfsd4_ssc_umount_item *nsui, struct file *filp,
> > > > > > > > > > > >        long timeout = msecs_to_jiffies(nfsd4_ssc_umount_timeout);
> > > > > > > > > > > >            nfs42_ssc_close(filp);
> > > > > > > > > > > > -    nfsd_file_put(dst);
> > > > > > > > > > > I think we still need this, in addition to release_copy_files called
> > > > > > > > > > > from cleanup_async_copy. For async inter-copy, there are 2 reference
> > > > > > > > > > > count added to the destination file, one from nfsd4_setup_inter_ssc
> > > > > > > > > > > and the other one from dup_copy_fields. The above nfsd_file_put is
> > > > > > > > > > > for
> > > > > > > > > > > the count added by dup_copy_fields.
> > > > > > > > > > > 
> > > > > > > > > > With this patch, the references held by the original copy structure
> > > > > > > > > > are
> > > > > > > > > > put by the call to release_copy_files at the end of nfsd4_copy. That
> > > > > > > > > > means that the kthread task is only responsible for putting the
> > > > > > > > > > references held by the (kmalloc'ed) async_copy structure. So, I think
> > > > > > > > > > this gets the nfsd_file refcounting right.
> > > > > > > > > Yes, I see. One refcount is decremented by release_copy_files at end
> > > > > > > > > of nfsd4_copy and another is decremented by release_copy_files in
> > > > > > > > > cleanup_async_copy.
> > > > > > > > > 
> > > > > > > > > > > >        fput(filp);
> > > > > > > > > > > >            spin_lock(&nn->nfsd_ssc_lock);
> > > > > > > > > > > > @@ -1562,13 +1561,6 @@ nfsd4_setup_intra_ssc(struct svc_rqst *rqstp,
> > > > > > > > > > > >                     &copy->nf_dst);
> > > > > > > > > > > >    }
> > > > > > > > > > > >    -static void
> > > > > > > > > > > > -nfsd4_cleanup_intra_ssc(struct nfsd_file *src, struct nfsd_file
> > > > > > > > > > > > *dst)
> > > > > > > > > > > > -{
> > > > > > > > > > > > -    nfsd_file_put(src);
> > > > > > > > > > > > -    nfsd_file_put(dst);
> > > > > > > > > > > > -}
> > > > > > > > > > > > -
> > > > > > > > > > > >    static void nfsd4_cb_offload_release(struct nfsd4_callback *cb)
> > > > > > > > > > > >    {
> > > > > > > > > > > >        struct nfsd4_cb_offload *cbo =
> > > > > > > > > > > > @@ -1683,12 +1675,18 @@ static void dup_copy_fields(struct
> > > > > > > > > > > > nfsd4_copy *src, struct nfsd4_copy *dst)
> > > > > > > > > > > >        dst->ss_nsui = src->ss_nsui;
> > > > > > > > > > > >    }
> > > > > > > > > > > >    +static void release_copy_files(struct nfsd4_copy *copy)
> > > > > > > > > > > > +{
> > > > > > > > > > > > +    if (copy->nf_src)
> > > > > > > > > > > > +        nfsd_file_put(copy->nf_src);
> > > > > > > > > > > > +    if (copy->nf_dst)
> > > > > > > > > > > > +        nfsd_file_put(copy->nf_dst);
> > > > > > > > > > > > +}
> > > > > > > > > > > > +
> > > > > > > > > > > >    static void cleanup_async_copy(struct nfsd4_copy *copy)
> > > > > > > > > > > >    {
> > > > > > > > > > > >        nfs4_free_copy_state(copy);
> > > > > > > > > > > > -    nfsd_file_put(copy->nf_dst);
> > > > > > > > > > > > -    if (!nfsd4_ssc_is_inter(copy))
> > > > > > > > > > > > -        nfsd_file_put(copy->nf_src);
> > > > > > > > > > > > +    release_copy_files(copy);
> > > > > > > > > > > >        spin_lock(&copy->cp_clp->async_lock);
> > > > > > > > > > > >        list_del(&copy->copies);
> > > > > > > > > > > > spin_unlock(&copy->cp_clp->async_lock);
> > > > > > > > > > > > @@ -1748,7 +1746,6 @@ static int nfsd4_do_async_copy(void *data)
> > > > > > > > > > > >        } else {
> > > > > > > > > > > >            nfserr = nfsd4_do_copy(copy, copy->nf_src->nf_file,
> > > > > > > > > > > >                           copy->nf_dst->nf_file, false);
> > > > > > > > > > > > -        nfsd4_cleanup_intra_ssc(copy->nf_src, copy->nf_dst);
> > > > > > > > > > > >        }
> > > > > > > > > > > >        do_callback:
> > > > > > > > > > > > @@ -1811,9 +1808,9 @@ nfsd4_copy(struct svc_rqst *rqstp, struct
> > > > > > > > > > > > nfsd4_compound_state *cstate,
> > > > > > > > > > > >        } else {
> > > > > > > > > > > >            status = nfsd4_do_copy(copy, copy->nf_src->nf_file,
> > > > > > > > > > > >                           copy->nf_dst->nf_file, true);
> > > > > > > > > > > > -        nfsd4_cleanup_intra_ssc(copy->nf_src, copy->nf_dst);
> > > > > > > > > > > >        }
> > > > > > > > > > > >    out:
> > > > > > > > > > > > +    release_copy_files(copy);
> > > > > > > > > > > >        return status;
> > > > > > > > > > > >    out_err:
> > > > > > > > > > > This is unrelated to the reference count issue.
> > > > > > > > > > > 
> > > > > > > > > > > Here if this is an inter-copy then we need to decrement the reference
> > > > > > > > > > > count of the nfsd4_ssc_umount_item so that the vfsmount can be
> > > > > > > > > > > unmounted
> > > > > > > > > > > later.
> > > > > > > > > > > 
> > > > > > > > > > Oh, I think I see what you mean. Maybe something like the (untested)
> > > > > > > > > > patch below on top of the original patch would fix that?
> > > > > > > > > > 
> > > > > > > > > > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> > > > > > > > > > index c9057462b973..7475c593553c 100644
> > > > > > > > > > --- a/fs/nfsd/nfs4proc.c
> > > > > > > > > > +++ b/fs/nfsd/nfs4proc.c
> > > > > > > > > > @@ -1511,8 +1511,10 @@ nfsd4_cleanup_inter_ssc(struct
> > > > > > > > > > nfsd4_ssc_umount_item *nsui, struct file *filp,
> > > > > > > > > >          struct nfsd_net *nn = net_generic(dst->nf_net, nfsd_net_id);
> > > > > > > > > >          long timeout = msecs_to_jiffies(nfsd4_ssc_umount_timeout);
> > > > > > > > > >   -       nfs42_ssc_close(filp);
> > > > > > > > > > -       fput(filp);
> > > > > > > > > > +       if (filp) {
> > > > > > > > > > +               nfs42_ssc_close(filp);
> > > > > > > > > > +               fput(filp);
> > > > > > > > > > +       }
> > > > > > > > > >             spin_lock(&nn->nfsd_ssc_lo
> > > > > > > > > >          list_del(&nsui->nsui_list);
> > > > > > > > > > @@ -1813,8 +1815,13 @@ nfsd4_copy(struct svc_rqst *rqstp, struct
> > > > > > > > > > nfsd4_compound_state *cstate,
> > > > > > > > > >          release_copy_files(copy);
> > > > > > > > > >          return status;
> > > > > > > > > >   out_err:
> > > > > > > > > > -       if (async_copy)
> > > > > > > > > > +       if (async_copy) {
> > > > > > > > > >                  cleanup_async_copy(async_copy);
> > > > > > > > > > +               if (nfsd4_ssc_is_inter(async_copy))
> > > > > > > > > We don't need to call nfsd4_cleanup_inter_ssc since the thread
> > > > > > > > > nfsd4_do_async_copy has not started yet so the file is not opened.
> > > > > > > > > We just need to do refcount_dec(&copy->ss_nsui->nsui_refcnt), unless
> > > > > > > > > you want to change nfsd4_cleanup_inter_ssc to detect this error
> > > > > > > > > condition and only decrement the reference count.
> > > > > > > > > 
> > > > > > > > Oh yeah, and this would break anyway since the nsui_list head is not
> > > > > > > > being initialized. Dai, would you mind spinning up a patch for this
> > > > > > > > since you're more familiar with the cleanup here?
> > > > > > > Will do. My patch will only fix the unmount issue. Your patch does
> > > > > > > the clean up potential nfsd_file refcount leaks in COPY codepath.
> > > > > > Or do you want me to merge your patch and mine into one?
> > > > > > 
> > > > > It probably is best to merge them, since backporters will probably want
> > > > > both patches anyway.
> > > > Unless these two changes are somehow interdependent, I'd like to keep
> > > > them separate. They address two separate issues, yes?
> > > 
> > > Yes.
> > > 
> > > > 
> > > > And -- narrow fixes need to go to nfsd-fixes, but clean-ups can wait
> > > > for nfsd-next. I'd rather not mix the two types of change.
> > > 
> > > Ok. Can we do this:
> > > 
> > > 1. Jeff's patch goes to nfsd-fixes since it has the fix for missing
> > > reference count.
> > 
> > To make sure I haven't lost track of anything:
> > 
> > The patch you refer to here is this one:
> > 
> > https://lore.kernel.org/linux-nfs/20230117193831.75201-3-jlayton@kernel.org/
> > 
> > Correct?
> > 
> > (I was waiting for Jeff and Olga to come to consensus, and I think
> > they have, so I can apply it to nfsd-fixes now).
> 
> Or not...
> 
> This one does not apply cleanly to nfsd-fixes, but does apply to nfsd-next.
> Also, the patch description says "clean up" and does not provide a Fixes:
> tag. So, either:
> 
>  - Jeff needs to test and redrive this patch against nfsd-fixes if we all
>    agree that it fixes a real and urgent bug, not a potential one; or
> 
>  - I will apply it as it stands to nfsd-next; or
> 
>  - You were referring to something else in 1. above.
> 
> Let me know how you'd both like to proceed.
> 

I'm fine with nfsd-next here. These are not a bugs that people are going
to hit under normal circumstances. It's something we need to fix, but
it's not urgent.
-- 
Jeff Layton <jlayton@kernel.org>