[PATCH] ipv6: fix lockdep splat in in6_dump_addrs()

[PATCH] ipv6: fix lockdep splat in in6_dump_addrs()

[Eric Dumazet]

As reported by syzbot, we should not use rcu_dereference()
when rcu_read_lock() is not held.

WARNING: suspicious RCU usage
5.19.0-rc2-syzkaller #0 Not tainted

net/ipv6/addrconf.c:5175 suspicious rcu_dereference_check() usage!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syz-executor326/3617:
 #0: ffffffff8d5848e8 (rtnl_mutex){+.+.}-{3:3}, at: netlink_dump+0xae/0xc20 net/netlink/af_netlink.c:2223

stack backtrace:
CPU: 0 PID: 3617 Comm: syz-executor326 Not tainted 5.19.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 in6_dump_addrs+0x12d1/0x1790 net/ipv6/addrconf.c:5175
 inet6_dump_addr+0x9c1/0xb50 net/ipv6/addrconf.c:5300
 netlink_dump+0x541/0xc20 net/netlink/af_netlink.c:2275
 __netlink_dump_start+0x647/0x900 net/netlink/af_netlink.c:2380
 netlink_dump_start include/linux/netlink.h:245 [inline]
 rtnetlink_rcv_msg+0x73e/0xc90 net/core/rtnetlink.c:6046
 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2501
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x543/0x7f0 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x917/0xe10 net/netlink/af_netlink.c:1921
 sock_sendmsg_nosec net/socket.c:714 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:734
 ____sys_sendmsg+0x6eb/0x810 net/socket.c:2492
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2546
 __sys_sendmsg net/socket.c:2575 [inline]
 __do_sys_sendmsg net/socket.c:2584 [inline]
 __se_sys_sendmsg net/socket.c:2582 [inline]
 __x64_sys_sendmsg+0x132/0x220 net/socket.c:2582
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x46/0xb0

Fixes: 88e2ca308094 ("mld: convert ifmcaddr6 to RCU")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Taehee Yoo <ap420073@gmail.com>
---
 net/ipv6/addrconf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 5864cbc30db69bc61483b2557fdc201e1a20f0a0..49cc6587dd771ac0bb17fbc31402785bcdd8ff18 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5168,9 +5168,9 @@ static int in6_dump_addrs(struct inet6_dev *idev, struct sk_buff *skb,
 		fillargs->event = RTM_GETMULTICAST;
 
 		/* multicast address */
-		for (ifmca = rcu_dereference(idev->mc_list);
+		for (ifmca = rtnl_dereference(idev->mc_list);
 		     ifmca;
-		     ifmca = rcu_dereference(ifmca->next), ip_idx++) {
+		     ifmca = rtnl_dereference(ifmca->next), ip_idx++) {
 			if (ip_idx < s_ip_idx)
 				continue;
 			err = inet6_fill_ifmcaddr(skb, ifmca, fillargs);
-- 
2.37.0.rc0.161.g10f37bed90-goog

Re: [PATCH] ipv6: fix lockdep splat in in6_dump_addrs()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Tue, 28 Jun 2022 12:12:48 +0000 you wrote:
> As reported by syzbot, we should not use rcu_dereference()
> when rcu_read_lock() is not held.
> 
> WARNING: suspicious RCU usage
> 5.19.0-rc2-syzkaller #0 Not tainted
> 
> net/ipv6/addrconf.c:5175 suspicious rcu_dereference_check() usage!
> 
> [...]

Here is the summary with links:
  - ipv6: fix lockdep splat in in6_dump_addrs()
    https://git.kernel.org/netdev/net/c/4e43e64d0f13

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

Re: [PATCH] ipv6: fix lockdep splat in in6_dump_addrs()

[Dan Carpenter]

On Tue, Jun 28, 2022 at 12:12:48PM +0000, Eric Dumazet wrote:
> As reported by syzbot, we should not use rcu_dereference()
> when rcu_read_lock() is not held.
> 

Is the comment at the top of the function out of date?

  5141  /* called with rcu_read_lock() */
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^

  5142  static int in6_dump_addrs(struct inet6_dev *idev, struct sk_buff *skb,
  5143                            struct netlink_callback *cb, int s_ip_idx,
  5144                            struct inet6_fill_args *fillargs)
  5145  {

regards,
dan carpenter