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

[Chuck Lever III <chuck.lever@oracle.com>]

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") ?


> Link: https://bugzilla.redhat.com/show_bug.cgi?id=2183056

This bug isn't publicly accessible, fwiw.


> 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