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Message-ID: <20250304125918.2763514-1-edumazet@google.com>
Date: Tue, 4 Mar 2025 12:59:18 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: David Ahern <dsahern@...nel.org>, Simon Horman <horms@...nel.org>, netdev@...r.kernel.org,
eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>,
syzbot+3f18ef0f7df107a3f6a0@...kaller.appspotmail.com
Subject: [PATCH net-next] inet: fix lwtunnel_valid_encap_type() lock imbalance
After blamed commit rtm_to_fib_config() now calls
lwtunnel_valid_encap_type{_attr}() without RTNL held,
triggering an unlock balance in __rtnl_unlock,
as reported by syzbot [1]
IPv6 and rtm_to_nh_config() are not yet converted.
Add a temporary @rtnl_is_held parameter to lwtunnel_valid_encap_type()
and lwtunnel_valid_encap_type_attr().
While we are at it replace the two rcu_dereference()
in lwtunnel_valid_encap_type() with more appropriate
rcu_access_pointer().
[1]
syz-executor245/5836 is trying to release lock (rtnl_mutex) at:
[<ffffffff89d0e38c>] __rtnl_unlock+0x6c/0xf0 net/core/rtnetlink.c:142
but there are no more locks to release!
other info that might help us debug this:
no locks held by syz-executor245/5836.
stack backtrace:
CPU: 0 UID: 0 PID: 5836 Comm: syz-executor245 Not tainted 6.14.0-rc4-syzkaller-00873-g3424291dd242 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
print_unlock_imbalance_bug+0x25b/0x2d0 kernel/locking/lockdep.c:5289
__lock_release kernel/locking/lockdep.c:5518 [inline]
lock_release+0x47e/0xa30 kernel/locking/lockdep.c:5872
__mutex_unlock_slowpath+0xec/0x800 kernel/locking/mutex.c:891
__rtnl_unlock+0x6c/0xf0 net/core/rtnetlink.c:142
lwtunnel_valid_encap_type+0x38a/0x5f0 net/core/lwtunnel.c:169
lwtunnel_valid_encap_type_attr+0x113/0x270 net/core/lwtunnel.c:209
rtm_to_fib_config+0x949/0x14e0 net/ipv4/fib_frontend.c:808
inet_rtm_newroute+0xf6/0x2a0 net/ipv4/fib_frontend.c:917
rtnetlink_rcv_msg+0x791/0xcf0 net/core/rtnetlink.c:6919
netlink_rcv_skb+0x206/0x480 net/netlink/af_netlink.c:2534
netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
netlink_unicast+0x7f6/0x990 net/netlink/af_netlink.c:1339
netlink_sendmsg+0x8de/0xcb0 net/netlink/af_netlink.c:1883
sock_sendmsg_nosec net/socket.c:709 [inline]
Fixes: 1dd2af7963e9 ("ipv4: fib: Convert RTM_NEWROUTE and RTM_DELROUTE to per-netns RTNL.")
Reported-by: syzbot+3f18ef0f7df107a3f6a0@...kaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/67c6f87a.050a0220.38b91b.0147.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
include/net/lwtunnel.h | 12 ++++++++----
net/core/lwtunnel.c | 23 ++++++++++++-----------
net/ipv4/fib_frontend.c | 4 ++--
net/ipv4/nexthop.c | 3 ++-
net/ipv6/route.c | 6 ++++--
5 files changed, 28 insertions(+), 20 deletions(-)
diff --git a/include/net/lwtunnel.h b/include/net/lwtunnel.h
index 53bd2d02a4f0db374b3920386afd12b0d7cbe6a0..39cd50300a1897883b9e4a6cfe95da257a5d007b 100644
--- a/include/net/lwtunnel.h
+++ b/include/net/lwtunnel.h
@@ -116,9 +116,11 @@ int lwtunnel_encap_add_ops(const struct lwtunnel_encap_ops *op,
int lwtunnel_encap_del_ops(const struct lwtunnel_encap_ops *op,
unsigned int num);
int lwtunnel_valid_encap_type(u16 encap_type,
- struct netlink_ext_ack *extack);
+ struct netlink_ext_ack *extack,
+ bool rtnl_is_held);
int lwtunnel_valid_encap_type_attr(struct nlattr *attr, int len,
- struct netlink_ext_ack *extack);
+ struct netlink_ext_ack *extack,
+ bool rtnl_is_held);
int lwtunnel_build_state(struct net *net, u16 encap_type,
struct nlattr *encap,
unsigned int family, const void *cfg,
@@ -201,13 +203,15 @@ static inline int lwtunnel_encap_del_ops(const struct lwtunnel_encap_ops *op,
}
static inline int lwtunnel_valid_encap_type(u16 encap_type,
- struct netlink_ext_ack *extack)
+ struct netlink_ext_ack *extack,
+ bool rtnl_is_held)
{
NL_SET_ERR_MSG(extack, "CONFIG_LWTUNNEL is not enabled in this kernel");
return -EOPNOTSUPP;
}
static inline int lwtunnel_valid_encap_type_attr(struct nlattr *attr, int len,
- struct netlink_ext_ack *extack)
+ struct netlink_ext_ack *extack,
+ bool rtnl_is_held)
{
/* return 0 since we are not walking attr looking for
* RTA_ENCAP_TYPE attribute on nexthops.
diff --git a/net/core/lwtunnel.c b/net/core/lwtunnel.c
index 711cd3b4347a7948ae3958257de1518685c7fbff..6d3833269c2b47584b8f0daab2e45b2b4953f3ca 100644
--- a/net/core/lwtunnel.c
+++ b/net/core/lwtunnel.c
@@ -147,7 +147,8 @@ int lwtunnel_build_state(struct net *net, u16 encap_type,
}
EXPORT_SYMBOL_GPL(lwtunnel_build_state);
-int lwtunnel_valid_encap_type(u16 encap_type, struct netlink_ext_ack *extack)
+int lwtunnel_valid_encap_type(u16 encap_type, struct netlink_ext_ack *extack,
+ bool rtnl_is_held)
{
const struct lwtunnel_encap_ops *ops;
int ret = -EINVAL;
@@ -158,21 +159,19 @@ int lwtunnel_valid_encap_type(u16 encap_type, struct netlink_ext_ack *extack)
return ret;
}
- rcu_read_lock();
- ops = rcu_dereference(lwtun_encaps[encap_type]);
- rcu_read_unlock();
+ ops = rcu_access_pointer(lwtun_encaps[encap_type]);
#ifdef CONFIG_MODULES
if (!ops) {
const char *encap_type_str = lwtunnel_encap_str(encap_type);
if (encap_type_str) {
- __rtnl_unlock();
+ if (rtnl_is_held)
+ __rtnl_unlock();
request_module("rtnl-lwt-%s", encap_type_str);
- rtnl_lock();
+ if (rtnl_is_held)
+ rtnl_lock();
- rcu_read_lock();
- ops = rcu_dereference(lwtun_encaps[encap_type]);
- rcu_read_unlock();
+ ops = rcu_access_pointer(lwtun_encaps[encap_type]);
}
}
#endif
@@ -185,7 +184,8 @@ int lwtunnel_valid_encap_type(u16 encap_type, struct netlink_ext_ack *extack)
EXPORT_SYMBOL_GPL(lwtunnel_valid_encap_type);
int lwtunnel_valid_encap_type_attr(struct nlattr *attr, int remaining,
- struct netlink_ext_ack *extack)
+ struct netlink_ext_ack *extack,
+ bool rtnl_is_held)
{
struct rtnexthop *rtnh = (struct rtnexthop *)attr;
struct nlattr *nla_entype;
@@ -207,7 +207,8 @@ int lwtunnel_valid_encap_type_attr(struct nlattr *attr, int remaining,
encap_type = nla_get_u16(nla_entype);
if (lwtunnel_valid_encap_type(encap_type,
- extack) != 0)
+ extack,
+ rtnl_is_held) != 0)
return -EOPNOTSUPP;
}
}
diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 6de77415b5b3003895bdee9e7fc36d3553c7c01a..3f4e629998fab4e2ae241c7efe40d9d162f8f517 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -807,7 +807,7 @@ static int rtm_to_fib_config(struct net *net, struct sk_buff *skb,
case RTA_MULTIPATH:
err = lwtunnel_valid_encap_type_attr(nla_data(attr),
nla_len(attr),
- extack);
+ extack, false);
if (err < 0)
goto errout;
cfg->fc_mp = nla_data(attr);
@@ -825,7 +825,7 @@ static int rtm_to_fib_config(struct net *net, struct sk_buff *skb,
case RTA_ENCAP_TYPE:
cfg->fc_encap_type = nla_get_u16(attr);
err = lwtunnel_valid_encap_type(cfg->fc_encap_type,
- extack);
+ extack, false);
if (err < 0)
goto errout;
break;
diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
index 09a3d73b45baa1e18f656bb4354bf2c9f707fe13..01df7dd795f01fe560c9f7d3bda2d9517b8368c9 100644
--- a/net/ipv4/nexthop.c
+++ b/net/ipv4/nexthop.c
@@ -3187,7 +3187,8 @@ static int rtm_to_nh_config(struct net *net, struct sk_buff *skb,
}
cfg->nh_encap_type = nla_get_u16(tb[NHA_ENCAP_TYPE]);
- err = lwtunnel_valid_encap_type(cfg->nh_encap_type, extack);
+ err = lwtunnel_valid_encap_type(cfg->nh_encap_type,
+ extack, true);
if (err < 0)
goto out;
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index ef2d23a1e3d532f5db37ca94ca482c5522dddffc..fb2e99a5652911a26bdb4b2bd0b867a688afdc82 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -5128,7 +5128,8 @@ static int rtm_to_fib6_config(struct sk_buff *skb, struct nlmsghdr *nlh,
cfg->fc_mp_len = nla_len(tb[RTA_MULTIPATH]);
err = lwtunnel_valid_encap_type_attr(cfg->fc_mp,
- cfg->fc_mp_len, extack);
+ cfg->fc_mp_len,
+ extack, true);
if (err < 0)
goto errout;
}
@@ -5147,7 +5148,8 @@ static int rtm_to_fib6_config(struct sk_buff *skb, struct nlmsghdr *nlh,
if (tb[RTA_ENCAP_TYPE]) {
cfg->fc_encap_type = nla_get_u16(tb[RTA_ENCAP_TYPE]);
- err = lwtunnel_valid_encap_type(cfg->fc_encap_type, extack);
+ err = lwtunnel_valid_encap_type(cfg->fc_encap_type,
+ extack, true);
if (err < 0)
goto errout;
}
--
2.48.1.711.g2feabab25a-goog
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