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@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/67c6f87a.050a0220.38b91b.0147.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250304125918.2763514-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/lwtunnel.h b/include/net/lwtunnel.h
index 53bd2d02a4f0db374b3920386afd12b0d7cbe6a0..39cd50300a1897883b9e4a6cfe95da257a5d007b 100644 (file)
--- 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 (file)
--- 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 (file)
--- 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 (file)
--- 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 (file)
--- 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;
        }