RE: [PATCH] nfsd: return -EINVAL when namelen is 0

[David Laight <David.Laight@ACULAB.COM>]

From: Scott Mayhew
> Sent: 09 September 2024 12:24
...
> > > > diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
> > > > index 67d8673a9391..69a3a84e159e 100644
> > > > --- a/fs/nfsd/nfs4recover.c
> > > > +++ b/fs/nfsd/nfs4recover.c
> > > > @@ -809,6 +809,10 @@ __cld_pipe_inprogress_downcall(const struct cld_msg_v2 __user *cmsg,
> > > >  			ci = &cmsg->cm_u.cm_clntinfo;
> > > >  			if (get_user(namelen, &ci->cc_name.cn_len))
> > > >  				return -EFAULT;
> > > > +			if (!namelen) {
> > > > +				dprintk("%s: namelen should not be zero", __func__);
> > > > +				return -EINVAL;
> > > > +			}
> > > >  			name.data = memdup_user(&ci->cc_name.cn_id, namelen);
> >
> > Don't you also want an upper bound sanity check?
> > (or is cn_len only 8 bit?)
> 
> Yeah, actually it should probably be checking for namelen >
> NFS4_OPAQUE_LIMIT.

I suspect memdup_user() itself should have a third 'maxlen' argument.
And probably one that is required to be a compile-time constant.

Oh, and is dprintk() rate-limited?
Not that the message looks very helpful.

	David

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