[rds-devel] [External] : Re: [PATCH net] rds: tcp: hold the net_device across ipv6_chk_addr() in rds_tcp_laddr_check()

[Xiang Mei]

On Thu, Jul 9, 2026 at 9:42 PM Allison Henderson <achender at kernel.org> wrote:
>
> On Thu, 2026-07-09 at 00:44 -0700, Xiang Mei wrote:
> > rds_tcp_laddr_check() looks up a scoped IPv6 interface with
> > dev_get_by_index_rcu(), drops the RCU read-side lock, and only then
> > passes the bare struct net_device * into ipv6_chk_addr().
> >
> > dev_get_by_index_rcu() only keeps the device alive within the same RCU
> > read-side section. After rcu_read_unlock(), a concurrent RTM_DELLINK can
> > free the net_device; ipv6_chk_addr() then dereferences the stale pointer
> > in __ipv6_chk_addr_and_flags() (e.g. l3mdev_master_dev_rcu(dev)), reading
> > freed memory.
> >
> > Take a reference with dev_hold() before dropping the RCU lock and release
> > it with dev_put() after ipv6_chk_addr(), so the device cannot be freed
> > while in use. dev_put(NULL) is a no-op, so the scope_id == 0 path is
> > unaffected.
> >
> >   BUG: KASAN: slab-use-after-free in __ipv6_chk_addr_and_flags (... net/ipv6/addrconf.c:1998)
> >   Read of size 8 at addr ffff8880106ec000 by task exploit/153
> >   Call Trace:
> >    ...
> >    kasan_report (mm/kasan/report.c:595)
> >    __ipv6_chk_addr_and_flags (... net/ipv6/addrconf.c:1998)
> >    ipv6_chk_addr (net/ipv6/addrconf.c:2031 net/ipv6/addrconf.c:1972)
> >    rds_tcp_laddr_check (net/rds/tcp.c:370)
> >    rds_bind (net/rds/bind.c:248)
> >    __sys_bind (net/socket.c:1920)
> >    __x64_sys_bind (net/socket.c:1956)
> >    do_syscall_64 (arch/x86/entry/syscall_64.c:63)
> >    entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
> >
> > Fixes: eee2fa6ab322 ("rds: Changing IP address internal representation to struct in6_addr")
> > Reported-by: Weiming Shi <bestswngs at gmail.com>
> > Assisted-by: Claude:claude-opus-4-8
> > Signed-off-by: Xiang Mei <xmei5 at asu.edu>
> > ---
> >  net/rds/tcp.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/net/rds/tcp.c b/net/rds/tcp.c
> > index a1de114d5e2e..204dcdc33c27 100644
> > --- a/net/rds/tcp.c
> > +++ b/net/rds/tcp.c
> > @@ -363,12 +363,16 @@ int rds_tcp_laddr_check(struct net *net, const struct in6_addr *addr,
> >                       rcu_read_unlock();
> >                       return -EADDRNOTAVAIL;
> >               }
> > +             dev_hold(dev);
> >               rcu_read_unlock();
> >       }
> >  #if IS_ENABLED(CONFIG_IPV6)
> >       ret = ipv6_chk_addr(net, addr, dev, 0);
> > +     dev_put(dev);
> Hi Xiang,
>
> Thanks for working on this.  It looks like this patch generated
> some CI warnings for dev_hold/put that should be addressed:
> https://patchwork.kernel.org/project/netdevbpf/patch/20260709074459.326345-1-xmei5@asu.edu/
>
> Per the comments from include/linux/netdevice.h:4546, netdev_hold/put
> replaced dev_hold/put, which takes a netdevice_tracker pointer.  But I
> think the easier way to do this may be just to widen the rcu locks already
> in this function.  Just move rcu_read_lock(); above the scope_id check,
> and make sure it's released before any returns.  That should get away from
> having to use the hold/puts all together.
>
>         rcu_read_lock();
>         if (scope_id != 0) {
>                 dev = dev_get_by_index_rcu(net, scope_id);
>                 if (!dev) {
>                         rcu_read_unlock();
>                         return -EADDRNOTAVAIL;
>                 }
>         }
> #if IS_ENABLED(CONFIG_IPV6)
>         ret = ipv6_chk_addr(net, addr, dev, 0);
>         if (ret) {
>                 rcu_read_unlock();
>                 return 0;
>         }
> #endif
>         rcu_read_unlock();
>         return -EADDRNOTAVAIL;
>
> Also, this patch conflicts with another submitted patch:
> [net,v2] rds: Fix inet6_addr_lst NULL dereference when IPv6 is disabled:
> https://patchwork.kernel.org/project/netdevbpf/patch/20260709162723.367523-1-Ilia.Gavrilov@infotecs.ru/
>
> So, please rebase on Ilia's v2, and mention the dependency in your change
> log so the stable folks pick them up in the right order.  Both fixes carry
> the same Fixes: tag so they should travel together.
>
> Thank you!
> Allison

Thanks so much! Your version is better!
I have sent v2, which rebase on Ilia's v2:
https://lore.kernel.org/netdev/20260710223029.1307043-1-xmei5@asu.edu/T/#u

Xiang


Xiang
>
> >       if (ret)
> >               return 0;
> > +#else
> > +     dev_put(dev);
> >  #endif
> >       return -EADDRNOTAVAIL;
> >  }
>