[PATCH 5.15 56/98] ipv6: fix lockdep splat in in6_dump_addrs()

Greg Kroah-Hartman
2022-07-05T12:31:10Z

From: Eric Dumazet <edumazet@google.com>

commit 4e43e64d0f1332fcc503babad4dc31aead7131ca upstream.

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>
Link: https://lore.kernel.org/r/20220628121248.858695-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv6/addrconf.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5166,9 +5166,9 @@ next:
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);