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

On Thu, Jul 9, 2026 at 9:42 PM Allison Henderson [off-list ref] wrote:

On Thu, 2026-07-09 at 00:44 -0700, Xiang Mei wrote:

quoted

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 <redacted>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Xiang Mei <redacted>
---
 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 (local)

Xiang


Xiang

quoted

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