ip6_mc_msfget() should be called under RTNL because it accesses RTNL
protected data. but the caller doesn't acquire rtnl_lock().
So, data couldn't be protected.
Therefore, it adds rtnl_lock() in do_ipv6_getsockopt(),
which is the caller of ip6_mc_msfget().
Splat looks like:
=============================
WARNING: suspicious RCU usage
5.12.0-rc4+ #480 Tainted: G W
-----------------------------
include/net/addrconf.h:314 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
1 lock held by sockopt_msfilte/4955:
#0: ffff88800aa21370 (sk_lock-AF_INET6){+.+.}-{0:0}, at: \
ipv6_get_msfilter+0xaf/0x190
stack backtrace:
Call Trace:
dump_stack+0xa4/0xe5
ip6_mc_find_dev_rtnl+0x117/0x150
ip6_mc_msfget+0x17d/0x700
? lock_acquire+0x191/0x720
? ipv6_sock_mc_join_ssm+0x10/0x10
? lockdep_hardirqs_on_prepare+0x3e0/0x3e0
? mark_held_locks+0xb7/0x120
? lockdep_hardirqs_on_prepare+0x27c/0x3e0
? __local_bh_enable_ip+0xa5/0xf0
? lock_sock_nested+0x82/0xf0
ipv6_get_msfilter+0xc3/0x190
? compat_ipv6_get_msfilter+0x300/0x300
? lock_downgrade+0x690/0x690
do_ipv6_getsockopt.isra.6.constprop.13+0x1706/0x29f0
? do_ipv6_mcast_group_source+0x150/0x150
? __wake_up_common+0x620/0x620
? mutex_trylock+0x23f/0x2a0
[ ... ]
Fixes: 88e2ca308094 ("mld: convert ifmcaddr6 to RCU")
Reported-by: Eric Dumazet <eduma...@google.com>
Signed-off-by: Taehee Yoo <ap420...@gmail.com>
---
commit 88e2ca308094 ("mld: convert ifmcaddr6 to RCU") is not yet merged
to "net" branch. So, target branch is "net-next"
net/ipv6/ipv6_sockglue.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index a6804a7e34c1..55dc35e09c68 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -1137,9 +1137,12 @@ static int do_ipv6_getsockopt(struct sock *sk, int
level, int optname,
val = sk->sk_family;
break;
case MCAST_MSFILTER:
+ rtnl_lock();
if (in_compat_syscall())
- return compat_ipv6_get_msfilter(sk, optval, optlen);
- return ipv6_get_msfilter(sk, optval, optlen, len);
+ val = compat_ipv6_get_msfilter(sk, optval, optlen);
+ val = ipv6_get_msfilter(sk, optval, optlen, len);
+ rtnl_unlock();
+ return val;
case IPV6_2292PKTOPTIONS:
{
struct msghdr msg;
--
2.17.1
