Re: [PATCH] nfsd: don't ignore the return code of svc_proc_register()

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2025-02-06 at 13:17 -0500, Chuck Lever wrote:
> On 2/6/25 1:12 PM, Jeff Layton wrote:
> > Currently, nfsd_proc_stat_init() ignores the return value of
> > svc_proc_register(). If the procfile creation fails, then the kernel
> > will WARN when it tries to remove the entry later.
> > 
> > Fix nfsd_proc_stat_init() to return the same type of pointer as
> > svc_proc_register(), and fix up nfsd_net_init() to check that and fail
> > the nfsd_net construction if it occurs.
> > 
> > svc_proc_register() can fail if the dentry can't be allocated, or if an
> > identical dentry already exists. The second case is pretty unlikely in
> > the nfsd_net construction codepath, so if this happens, return -ENOMEM.
> > 
> > Fixes: 93483ac5fec6 ("nfsd: expose /proc/net/sunrpc/nfsd in net namespaces")
> > Reported-by: syzbot+e34ad04f27991521104c@syzkaller.appspotmail.com
> > Closes: https://lore.kernel.org/linux-nfs/67a47501.050a0220.19061f.05f9.GAE@google.com/
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> > I looked at the console log from the report, and syzkaller is doing
> > fault injection on allocations. You can see the stack where the "nfsd"
> > directory under /proc failed to be created due to one. This is a pretty
> > unlikely bug under normal circumstances, but it's simple to fix. The
> > problem predates the patch in Fixes:, but it's not worth the effort to
> > backport this to anything earlier.
> 
> I'd prefer to document this by labeling the actual commit that
> introduced the problem in the Fixes: tag, then using
> 
> "Cc: stable # vN.M"
> 
> to block automatic backporting to LTS kernels where this patch won't
> apply cleanly. I can derive the values of N and M from the commit you
> mention above, but do you happen to know the actual culprit commit?
> 
> 

Unfortunately this bug goes back to the initial 2.6.12 import into git.
I didn't look earlier. Note that nfsd is not alone here. Ignoring the
result of proc_create_data() is very common.

If you want to drop the Fixes: tag, and add the Cc: stable instead,
then that's fine with me. Whatever works best.


> > ---
> >  fs/nfsd/nfsctl.c | 9 ++++++++-
> >  fs/nfsd/stats.c  | 4 ++--
> >  fs/nfsd/stats.h  | 2 +-
> >  3 files changed, 11 insertions(+), 4 deletions(-)
> > 
> > diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> > index 95ea4393305bd38493b640fbaba2e8f57f5a501d..583eda0df54dca394de4bbe8d148be2892df39cb 100644
> > --- a/fs/nfsd/nfsctl.c
> > +++ b/fs/nfsd/nfsctl.c
> > @@ -2204,8 +2204,14 @@ static __net_init int nfsd_net_init(struct net *net)
> >  					  NFSD_STATS_COUNTERS_NUM);
> >  	if (retval)
> >  		goto out_repcache_error;
> > +
> >  	memset(&nn->nfsd_svcstats, 0, sizeof(nn->nfsd_svcstats));
> >  	nn->nfsd_svcstats.program = &nfsd_programs[0];
> > +	if (!nfsd_proc_stat_init(net)) {
> > +		retval = -ENOMEM;
> > +		goto out_proc_error;
> > +	}
> > +
> >  	for (i = 0; i < sizeof(nn->nfsd_versions); i++)
> >  		nn->nfsd_versions[i] = nfsd_support_version(i);
> >  	for (i = 0; i < sizeof(nn->nfsd4_minorversions); i++)
> > @@ -2215,12 +2221,13 @@ static __net_init int nfsd_net_init(struct net *net)
> >  	nfsd4_init_leases_net(nn);
> >  	get_random_bytes(&nn->siphash_key, sizeof(nn->siphash_key));
> >  	seqlock_init(&nn->writeverf_lock);
> > -	nfsd_proc_stat_init(net);
> >  #if IS_ENABLED(CONFIG_NFS_LOCALIO)
> >  	INIT_LIST_HEAD(&nn->local_clients);
> >  #endif
> >  	return 0;
> >  
> > +out_proc_error:
> > +	percpu_counter_destroy_many(nn->counter, NFSD_STATS_COUNTERS_NUM);
> >  out_repcache_error:
> >  	nfsd_idmap_shutdown(net);
> >  out_idmap_error:
> > diff --git a/fs/nfsd/stats.c b/fs/nfsd/stats.c
> > index bb22893f1157e4c159e123b6d8e25b8eab52e187..f7eaf95e20fc8758566f469c6c2de79119fea070 100644
> > --- a/fs/nfsd/stats.c
> > +++ b/fs/nfsd/stats.c
> > @@ -73,11 +73,11 @@ static int nfsd_show(struct seq_file *seq, void *v)
> >  
> >  DEFINE_PROC_SHOW_ATTRIBUTE(nfsd);
> >  
> > -void nfsd_proc_stat_init(struct net *net)
> > +struct proc_dir_entry *nfsd_proc_stat_init(struct net *net)
> >  {
> >  	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
> >  
> > -	svc_proc_register(net, &nn->nfsd_svcstats, &nfsd_proc_ops);
> > +	return svc_proc_register(net, &nn->nfsd_svcstats, &nfsd_proc_ops);
> >  }
> >  
> >  void nfsd_proc_stat_shutdown(struct net *net)
> > diff --git a/fs/nfsd/stats.h b/fs/nfsd/stats.h
> > index 04aacb6c36e2576ba231ee481e3a3e9e9f255a61..e4efb0e4e56d467c13eaa5a1dd312c85dadeb4b8 100644
> > --- a/fs/nfsd/stats.h
> > +++ b/fs/nfsd/stats.h
> > @@ -10,7 +10,7 @@
> >  #include <uapi/linux/nfsd/stats.h>
> >  #include <linux/percpu_counter.h>
> >  
> > -void nfsd_proc_stat_init(struct net *net);
> > +struct proc_dir_entry *nfsd_proc_stat_init(struct net *net);
> >  void nfsd_proc_stat_shutdown(struct net *net);
> >  
> >  static inline void nfsd_stats_rc_hits_inc(struct nfsd_net *nn)
> > 
> > ---
> > base-commit: ebbdc9429c39336a406b191cfe84bca2c12c2f73
> > change-id: 20250206-nfsd-fixes-8e61bdf66347
> > 
> > Best regards,
> 
> 

-- 
Jeff Layton <jlayton@kernel.org>