[PATCH net v3] rds: tcp: hold the RCU lock across ipv6_chk_addr() in rds_tcp_laddr_check()

[PATCH net v3] rds: tcp: hold the RCU lock across ipv6_chk_addr() in rds_tcp_laddr_check()

[Xiang Mei]

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)

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

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>
Reviewed-by: Allison Henderson <achender@kernel.org>
---
v2: Use rcu_read_locks and rebase on rds: Fix inet6_addr_lst NULL 
    dereference when IPv6 is disabled
v3: Add change log to commit message as Allison suggested


 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;
 }
 
-- 
2.43.0

Re: [PATCH net v3] rds: tcp: hold the RCU lock across ipv6_chk_addr() in rds_tcp_laddr_check()

[Jakub Kicinski]

On Tue, 14 Jul 2026 14:22:39 -0700 Xiang Mei wrote:
> 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

Why did you(r LLM) leave this portion of the change log in here and the
rest in the correct place below?

> 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>
> Reviewed-by: Allison Henderson <achender@kernel.org>
> ---
> v2: Use rcu_read_locks and rebase on rds: Fix inet6_addr_lst NULL 
>     dereference when IPv6 is disabled
> v3: Add change log to commit message as Allison suggested

The patch does not apply, if it's still relevant please rebase and
repost.
-- 
pw-bot: cr

Re: [PATCH net v3] rds: tcp: hold the RCU lock across ipv6_chk_addr() in rds_tcp_laddr_check()

[Xiang Mei]

On Wed, Jul 22, 2026 at 11:27 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Tue, 14 Jul 2026 14:22:39 -0700 Xiang Mei wrote:
> > 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
>
> Why did you(r LLM) leave this portion of the change log in here and the
> rest in the correct place below?
>
I added that based on Allison Henderson's suggestion of v2. I don't
know how the change log works, so I may misunderstand Allison's
suggestion.
I'll do some research to fix that in v4.
(https://lore.kernel.org/all/f69ec0975481ad04dc7403834bbb6b93d1092ecb.camel%40kernel.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>
> > Reviewed-by: Allison Henderson <achender@kernel.org>
> > ---
> > v2: Use rcu_read_locks and rebase on rds: Fix inet6_addr_lst NULL
> >     dereference when IPv6 is disabled
> > v3: Add change log to commit message as Allison suggested
>
> The patch does not apply, if it's still relevant please rebase and
> repost.
> --
> pw-bot: cr

I'll check the rebase issue, thanks.

Xiang

Re: [PATCH net v3] rds: tcp: hold the RCU lock across ipv6_chk_addr() in rds_tcp_laddr_check()

[Xiang Mei]

On Wed, Jul 22, 2026 at 11:27 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Tue, 14 Jul 2026 14:22:39 -0700 Xiang Mei wrote:
> > 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
>
> Why did you(r LLM) leave this portion of the change log in here and the
> rest in the correct place below?

Sorry for the weird message. It was my misunderstanding; I
misunderstood Allison's message. I thought it was additional changelog
in the commit message. But it was that I forgot to have a changelog in
my v2. (I get used to v1:... and v2: ... so I thought Changes since v1
is like something I should put in the commit message.)

>
> > 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>
> > Reviewed-by: Allison Henderson <achender@kernel.org>
> > ---
> > v2: Use rcu_read_locks and rebase on rds: Fix inet6_addr_lst NULL
> >     dereference when IPv6 is disabled
> > v3: Add change log to commit message as Allison suggested
>
> The patch does not apply, if it's still relevant please rebase and
> repost.

The v3 applies to the latest net.git (8e04823c120b). So no content is
changed in v4:
https://lore.kernel.org/netdev/20260722210203.565803-1-xmei5@asu.edu/T/#u

Thanks for your time.

Xiang
> --
> pw-bot: cr