Re: [PATCH] sunrpc: only free unix grouplist after RCU settles

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2023-03-30 at 18:31 +0000, Chuck Lever III wrote:
> Hi Jeff-
> 
> > On Mar 30, 2023, at 2:24 PM, Jeff Layton <jlayton@kernel.org> wrote:
> > 
> > While the unix_gid object is rcu-freed, the group_info list that it
> > contains is not. Ensure that we only put the group list reference once
> > we are really freeing the unix_gid object.
> > 
> > Reported-by: Zhi Li <yieli@redhat.com>
> 
> Should we also add
> 
> Fixes: fd5d2f78261b ("SUNRPC: Make server side AUTH_UNIX use lockless lookups") ?
> 
> 

Sure. That does look like when that particular bug crept in.
 
> > Link: https://bugzilla.redhat.com/show_bug.cgi?id=2183056
> 
> This bug isn't publicly accessible, fwiw.
> 

Thanks. It should be now.

> 
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> > net/sunrpc/svcauth_unix.c | 17 +++++++++++++----
> > 1 file changed, 13 insertions(+), 4 deletions(-)
> > 
> > diff --git a/net/sunrpc/svcauth_unix.c b/net/sunrpc/svcauth_unix.c
> > index 50e2eb579194..4485088ce27b 100644
> > --- a/net/sunrpc/svcauth_unix.c
> > +++ b/net/sunrpc/svcauth_unix.c
> > @@ -416,14 +416,23 @@ static int unix_gid_hash(kuid_t uid)
> > 	return hash_long(from_kuid(&init_user_ns, uid), GID_HASHBITS);
> > }
> > 
> > -static void unix_gid_put(struct kref *kref)
> > +static void unix_gid_free(struct rcu_head *rcu)
> > {
> > -	struct cache_head *item = container_of(kref, struct cache_head, ref);
> > -	struct unix_gid *ug = container_of(item, struct unix_gid, h);
> > +	struct unix_gid *ug = container_of(rcu, struct unix_gid, rcu);
> > +	struct cache_head *item = &ug->h;
> > +
> > 	if (test_bit(CACHE_VALID, &item->flags) &&
> > 	    !test_bit(CACHE_NEGATIVE, &item->flags))
> > 		put_group_info(ug->gi);
> > -	kfree_rcu(ug, rcu);
> > +	kfree(ug);
> > +}
> > +
> > +static void unix_gid_put(struct kref *kref)
> > +{
> > +	struct cache_head *item = container_of(kref, struct cache_head, ref);
> > +	struct unix_gid *ug = container_of(item, struct unix_gid, h);
> > +
> > +	call_rcu(&ug->rcu, unix_gid_free);
> > }
> > 
> > static int unix_gid_match(struct cache_head *corig, struct cache_head *cnew)
> > -- 
> > 2.39.2
> > 
> 
> --
> Chuck Lever
> 
> 

-- 
Jeff Layton <jlayton@kernel.org>