Re: [PATCH] netlink: fix potential race issue in netlink_native_seq_show()

[nai lin <ayano2023th@gmail.com>]

On Wed, Jan 17, 2024 at 11:28:24AM +0100, Eric Dumazet wrote:
> On Wed, Jan 17, 2024 at 9:38 AM nai lin <ayano2023th@gmail.com> wrote:
> >
> > Access to the nlk group should be protected by netlink_lock_table() like
> > commit <f773608026ee> ("netlink: access nlk groups safely in netlink bind
> > and getname"), otherwise there will be potential race conditions.
> >
> > Signed-off-by: nai lin <ayano2023th@gmail.com>
> 
> OK, I think you forgot to include this tag I suggested earlier to you.
> 
> Fixes: e341694e3eb5 ("netlink: Convert netlink_lookup() to use RCU
> protected hash table")
> 
Sorry I forgot to include fix tag, thank you for pointing out my problem
and thank you very much for your work.
> > ---
> >  net/netlink/af_netlink.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> > index 4ed8ffd58ff3..61ad81fb80f5 100644
> > --- a/net/netlink/af_netlink.c
> > +++ b/net/netlink/af_netlink.c
> > @@ -2693,6 +2693,7 @@ static int netlink_native_seq_show(struct seq_file *seq, void *v)
> >                 struct sock *s = v;
> >                 struct netlink_sock *nlk = nlk_sk(s);
> >
> > +               netlink_lock_table();
> 
> netlink_lock_table() is heavy weight, appropriate for contexts where
> we might sleep.
> 
> We could instead use a helper to acquire the lock for a very small period.
> 
> diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> index 4ed8ffd58ff375f3fa9f262e6f3b4d1a1aaf2731..c50ca0f5adfb9691e6df37b4ac518b95c2d7908f
> 100644
> --- a/net/netlink/af_netlink.c
> +++ b/net/netlink/af_netlink.c
> @@ -1136,6 +1136,18 @@ static int netlink_connect(struct socket *sock,
> struct sockaddr *addr,
>         return err;
>  }
> 
> +static u32 netlink_get_groups_mask(const struct netlink_sock *nlk)
> +{
> +       unsigned long flags;
> +       u32 res;
> +
> +       read_lock_irqsave(&nl_table_lock, flags);
> +       res = nlk->groups ? nlk->groups[0] : 0;
> +       read_unlock_irqrestore(&nl_table_lock, flags);
> +
> +       return res;
> +}
> +
>  static int netlink_getname(struct socket *sock, struct sockaddr *addr,
>                            int peer)
>  {
> @@ -1153,9 +1165,7 @@ static int netlink_getname(struct socket *sock,
> struct sockaddr *addr,
>         } else {
>                 /* Paired with WRITE_ONCE() in netlink_insert() */
>                 nladdr->nl_pid = READ_ONCE(nlk->portid);
> -               netlink_lock_table();
> -               nladdr->nl_groups = nlk->groups ? nlk->groups[0] : 0;
> -               netlink_unlock_table();
> +               nladdr->nl_groups = netlink_get_groups_mask(nlk);
>         }
>         return sizeof(*nladdr);
>  }
> @@ -2697,7 +2707,7 @@ static int netlink_native_seq_show(struct
> seq_file *seq, void *v)
>                            s,
>                            s->sk_protocol,
>                            nlk->portid,
> -                          nlk->groups ? (u32)nlk->groups[0] : 0,
> +                          netlink_get_groups_mask(nlk),
>                            sk_rmem_alloc_get(s),
>                            sk_wmem_alloc_get(s),
>                            READ_ONCE(nlk->cb_running),