Re: [PATCH net v2] rds: tcp: hold the RCU lock across ipv6_chk_addr() in rds_tcp_laddr_check()

[Allison Henderson <achender@kernel.org>]

On Fri, 2026-07-10 at 15:30 -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.
> 
> Keep the RCU read-side lock held across the ipv6_chk_addr() call instead
> of dropping it right after the lookup, so the device cannot be freed
> while it is in use.
> 
>   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)
> 



Thanks Xiang!  Just more thing to make sure your patches gets through. Add a change log here like this:

Changes since v1:
  Use rcu_read_locks instead of dev_hold/put
  Rebased on [PATCH net v2] rds: Fix inet6_addr_lst NULL dereference when IPv6 is disabled

Changes since v2:
  Add change log


Otherwise, it might get bounced if they happen to try your patch first.
With that fixed:  
Reviewed-by: Allison Henderson <achender@kernel.org>

Thanks!
Allison

> Thanks Xiang!  Just more thing to make sure your patches gets through. Add a change log here like this:
> 
> Changes since v1:
>   Use rcu_read_locks instead of dev_hold/put
>   Rebased on [PATCH net v2] rds: Fix inet6_addr_lst NULL dereference when IPv6 is disabled
> 
> Changes since v2:
>   Add change log
> 
> Reviewed-by: Allison Henderson <achender@kernel.org>
> Fixes: eee2fa6ab322 ("rds: Changing IP address internal representation to struct in6_addr")
> Reported-by: Weiming Shi <bestswngs@gmail.com>
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Xiang Mei <xmei5@asu.edu>
> ---
>  net/rds/tcp.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/net/rds/tcp.c b/net/rds/tcp.c
> index 955d92277d5a..30cfb0087f2c 100644
> --- a/net/rds/tcp.c
> +++ b/net/rds/tcp.c
> @@ -355,23 +355,25 @@ int rds_tcp_laddr_check(struct net *net, const struct in6_addr *addr,
>  	/* If the scope_id is specified, check only those addresses
>  	 * hosted on the specified interface.
>  	 */
> +	rcu_read_lock();
>  	if (scope_id != 0) {
> -		rcu_read_lock();
>  		dev = dev_get_by_index_rcu(net, scope_id);
>  		/* scope_id is not valid... */
>  		if (!dev) {
>  			rcu_read_unlock();
>  			return -EADDRNOTAVAIL;
>  		}
> -		rcu_read_unlock();
>  	}
>  #if IS_ENABLED(CONFIG_IPV6)
>  	if (ipv6_mod_enabled()) {
>  		ret = ipv6_chk_addr(net, addr, dev, 0);
> -		if (ret)
> +		if (ret) {
> +			rcu_read_unlock();
>  			return 0;
> +		}
>  	}
>  #endif
> +	rcu_read_unlock();
>  	return -EADDRNOTAVAIL;
>  }
>