[PATCH net 0/3] net: fix mcast RCU splats

[PATCH net 0/3] net: fix mcast RCU splats

[Paolo Abeni]

This series addresses the RCU splat triggered by the forwarding
mroute tests.

The first patch does not address any specific issue, but makes the
following ones more clear. Patch 2 and 3 address the issue for ipv6 and
ipv4 respectively.

Paolo Abeni (3):
  ipmr: add debug check for mr table cleanup
  ip6mr: fix tables suspicious RCU usage
  ipmr: fix tables suspicious RCU usage

 net/ipv4/ipmr.c  | 51 ++++++++++++++++++++++++++++++++++++------------
 net/ipv6/ip6mr.c | 47 +++++++++++++++++++++++++++++++++-----------
 2 files changed, 74 insertions(+), 24 deletions(-)

-- 
2.45.2

[PATCH net 1/3] ipmr: add debug check for mr table cleanup

[Paolo Abeni]

The multicast route tables lifecycle, for both ipv4 and ipv6, is
protected by RCU using the RTNL lock for write access. In many
places a table pointer escapes the RCU (or RTNL) protected critical
section, but such scenarios are actually safe because tables are
deleted only at namespace cleanup time or just after allocation, in
case of default rule creation failure.

Tables freed at namespace cleanup time are assured to be alive for the
whole netns lifetime; tables freed just after creation time are never
exposed to other possible users.

Ensure that the free conditions are respected in ip{,6}mr_free_table, to
document the locking schema and to prevent future possible introduction
of 'table del' operation from breaking it.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/ipv4/ipmr.c  | 9 +++++++++
 net/ipv6/ip6mr.c | 9 +++++++++
 2 files changed, 18 insertions(+)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index c58dd78509a2..c6ad01dc8310 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -358,6 +358,11 @@ bool ipmr_rule_default(const struct fib_rule *rule)
 EXPORT_SYMBOL(ipmr_rule_default);
 #endif
 
+static bool ipmr_can_free_table(struct net *net)
+{
+	return !check_net(net) || !net->ipv4.mr_rules_ops;
+}
+
 static inline int ipmr_hash_cmp(struct rhashtable_compare_arg *arg,
 				const void *ptr)
 {
@@ -413,6 +418,10 @@ static struct mr_table *ipmr_new_table(struct net *net, u32 id)
 
 static void ipmr_free_table(struct mr_table *mrt)
 {
+	struct net *net = read_pnet(&mrt->net);
+
+	DEBUG_NET_WARN_ON_ONCE(!ipmr_can_free_table(net));
+
 	timer_shutdown_sync(&mrt->ipmr_expire_timer);
 	mroute_clean_tables(mrt, MRT_FLUSH_VIFS | MRT_FLUSH_VIFS_STATIC |
 				 MRT_FLUSH_MFC | MRT_FLUSH_MFC_STATIC);
diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index d66f58932a79..275784a8f35b 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -341,6 +341,11 @@ static unsigned int ip6mr_rules_seq_read(const struct net *net)
 }
 #endif
 
+static bool ip6mr_can_free_table(struct net *net)
+{
+	return !check_net(net) || !net->ipv6.mr6_rules_ops;
+}
+
 static int ip6mr_hash_cmp(struct rhashtable_compare_arg *arg,
 			  const void *ptr)
 {
@@ -392,6 +397,10 @@ static struct mr_table *ip6mr_new_table(struct net *net, u32 id)
 
 static void ip6mr_free_table(struct mr_table *mrt)
 {
+	struct net *net = read_pnet(&mrt->net);
+
+	DEBUG_NET_WARN_ON_ONCE(!ip6mr_can_free_table(net));
+
 	timer_shutdown_sync(&mrt->ipmr_expire_timer);
 	mroute_clean_tables(mrt, MRT6_FLUSH_MIFS | MRT6_FLUSH_MIFS_STATIC |
 				 MRT6_FLUSH_MFC | MRT6_FLUSH_MFC_STATIC);
-- 
2.45.2

Re: [PATCH net 1/3] ipmr: add debug check for mr table cleanup

[Paolo Abeni]

On 11/22/24 12:02, Paolo Abeni wrote:
> diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
> index c58dd78509a2..c6ad01dc8310 100644
> --- a/net/ipv4/ipmr.c
> +++ b/net/ipv4/ipmr.c
> @@ -358,6 +358,11 @@ bool ipmr_rule_default(const struct fib_rule *rule)
>  EXPORT_SYMBOL(ipmr_rule_default);
>  #endif
>  
> +static bool ipmr_can_free_table(struct net *net)
> +{
> +	return !check_net(net) || !net->ipv4.mr_rules_ops;

Not so good. mr_rules_ops exists only for
CONFIG_IP_MROUTE_MULTIPLE_TABLES builds.

/P

Re: [PATCH net 1/3] ipmr: add debug check for mr table cleanup

[kernel test robot]

Hi Paolo,

kernel test robot noticed the following build errors:

[auto build test ERROR on net/main]

url:    https://github.com/intel-lab-lkp/linux/commits/Paolo-Abeni/ipmr-add-debug-check-for-mr-table-cleanup/20241125-104108
base:   net/main
patch link:    https://lore.kernel.org/r/23bd87600f046ce1f1c93513b6ac8f8152b22bf4.1732270911.git.pabeni%40redhat.com
patch subject: [PATCH net 1/3] ipmr: add debug check for mr table cleanup
config: sh-se7712_defconfig (https://download.01.org/0day-ci/archive/20241125/202411251504.ZKzltGDp-lkp@intel.com/config)
compiler: sh4-linux-gcc (GCC) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241125/202411251504.ZKzltGDp-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202411251504.ZKzltGDp-lkp@intel.com/

All errors (new ones prefixed by >>):

   net/ipv4/ipmr.c: In function 'ipmr_can_free_table':
>> net/ipv4/ipmr.c:363:46: error: 'struct netns_ipv4' has no member named 'mr_rules_ops'; did you mean 'rules_ops'?
     363 |         return !check_net(net) || !net->ipv4.mr_rules_ops;
         |                                              ^~~~~~~~~~~~
         |                                              rules_ops


vim +363 net/ipv4/ipmr.c

   360	
   361	static bool ipmr_can_free_table(struct net *net)
   362	{
 > 363		return !check_net(net) || !net->ipv4.mr_rules_ops;
   364	}
   365	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH net 1/3] ipmr: add debug check for mr table cleanup

[kernel test robot]

Hi Paolo,

kernel test robot noticed the following build errors:

[auto build test ERROR on net/main]

url:    https://github.com/intel-lab-lkp/linux/commits/Paolo-Abeni/ipmr-add-debug-check-for-mr-table-cleanup/20241125-104108
base:   net/main
patch link:    https://lore.kernel.org/r/23bd87600f046ce1f1c93513b6ac8f8152b22bf4.1732270911.git.pabeni%40redhat.com
patch subject: [PATCH net 1/3] ipmr: add debug check for mr table cleanup
config: mips-ip22_defconfig (https://download.01.org/0day-ci/archive/20241125/202411251722.Mg6UtrLH-lkp@intel.com/config)
compiler: mips-linux-gcc (GCC) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241125/202411251722.Mg6UtrLH-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202411251722.Mg6UtrLH-lkp@intel.com/

All errors (new ones prefixed by >>):

   net/ipv6/ip6mr.c: In function 'ip6mr_can_free_table':
>> net/ipv6/ip6mr.c:346:46: error: 'struct netns_ipv6' has no member named 'mr6_rules_ops'; did you mean 'fib6_rules_ops'?
     346 |         return !check_net(net) || !net->ipv6.mr6_rules_ops;
         |                                              ^~~~~~~~~~~~~
         |                                              fib6_rules_ops


vim +346 net/ipv6/ip6mr.c

   343	
   344	static bool ip6mr_can_free_table(struct net *net)
   345	{
 > 346		return !check_net(net) || !net->ipv6.mr6_rules_ops;
   347	}
   348	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH net 1/3] ipmr: add debug check for mr table cleanup

[kernel test robot]

Hi Paolo,

kernel test robot noticed the following build warnings:

[auto build test WARNING on net/main]

url:    https://github.com/intel-lab-lkp/linux/commits/Paolo-Abeni/ipmr-add-debug-check-for-mr-table-cleanup/20241125-104108
base:   net/main
patch link:    https://lore.kernel.org/r/23bd87600f046ce1f1c93513b6ac8f8152b22bf4.1732270911.git.pabeni%40redhat.com
patch subject: [PATCH net 1/3] ipmr: add debug check for mr table cleanup
config: arc-randconfig-001-20241126 (https://download.01.org/0day-ci/archive/20241126/202411260343.02pIupsk-lkp@intel.com/config)
compiler: arceb-elf-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241126/202411260343.02pIupsk-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202411260343.02pIupsk-lkp@intel.com/

All warnings (new ones prefixed by >>):

   net/ipv4/ipmr.c: In function 'ipmr_can_free_table':
   net/ipv4/ipmr.c:363:46: error: 'struct netns_ipv4' has no member named 'mr_rules_ops'; did you mean 'rules_ops'?
     363 |         return !check_net(net) || !net->ipv4.mr_rules_ops;
         |                                              ^~~~~~~~~~~~
         |                                              rules_ops
>> net/ipv4/ipmr.c:364:1: warning: control reaches end of non-void function [-Wreturn-type]
     364 | }
         | ^


vim +364 net/ipv4/ipmr.c

   360	
   361	static bool ipmr_can_free_table(struct net *net)
   362	{
 > 363		return !check_net(net) || !net->ipv4.mr_rules_ops;
 > 364	}
   365	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

[PATCH net 2/3] ip6mr: fix tables suspicious RCU usage

[Paolo Abeni]

Several places call ip6mr_get_table() with no RCU nor RTNL lock.
Add RCU protection inside such helper and provide a lockless variant
for the few callers that already acquired the relevant lock.

Note that some users additionally reference the table outside the RCU
lock. That is actually safe as the table deletion can happen only
after all table accesses are completed.

Fixes: e2d57766e674 ("net: Provide compat support for SIOCGETMIFCNT_IN6 and SIOCGETSGCNT_IN6.")
Fixes: d7c31cbde4bc ("net: ip6mr: add RTM_GETROUTE netlink op")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/ipv6/ip6mr.c | 38 +++++++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 11 deletions(-)

diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 275784a8f35b..c7eeb0694621 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -125,7 +125,7 @@ static struct mr_table *ip6mr_mr_table_iter(struct net *net,
 	return ret;
 }
 
-static struct mr_table *ip6mr_get_table(struct net *net, u32 id)
+static struct mr_table *__ip6mr_get_table(struct net *net, u32 id)
 {
 	struct mr_table *mrt;
 
@@ -136,6 +136,16 @@ static struct mr_table *ip6mr_get_table(struct net *net, u32 id)
 	return NULL;
 }
 
+static struct mr_table *ip6mr_get_table(struct net *net, u32 id)
+{
+	struct mr_table *mrt;
+
+	rcu_read_lock();
+	mrt = __ip6mr_get_table(net, id);
+	rcu_read_unlock();
+	return mrt;
+}
+
 static int ip6mr_fib_lookup(struct net *net, struct flowi6 *flp6,
 			    struct mr_table **mrt)
 {
@@ -177,7 +187,7 @@ static int ip6mr_rule_action(struct fib_rule *rule, struct flowi *flp,
 
 	arg->table = fib_rule_get_table(rule, arg);
 
-	mrt = ip6mr_get_table(rule->fr_net, arg->table);
+	mrt = __ip6mr_get_table(rule->fr_net, arg->table);
 	if (!mrt)
 		return -EAGAIN;
 	res->mrt = mrt;
@@ -304,6 +314,8 @@ static struct mr_table *ip6mr_get_table(struct net *net, u32 id)
 	return net->ipv6.mrt6;
 }
 
+#define __ip6mr_get_table ip6mr_get_table
+
 static int ip6mr_fib_lookup(struct net *net, struct flowi6 *flp6,
 			    struct mr_table **mrt)
 {
@@ -387,7 +399,7 @@ static struct mr_table *ip6mr_new_table(struct net *net, u32 id)
 {
 	struct mr_table *mrt;
 
-	mrt = ip6mr_get_table(net, id);
+	mrt = __ip6mr_get_table(net, id);
 	if (mrt)
 		return mrt;
 
@@ -420,13 +432,15 @@ static void *ip6mr_vif_seq_start(struct seq_file *seq, loff_t *pos)
 	struct net *net = seq_file_net(seq);
 	struct mr_table *mrt;
 
-	mrt = ip6mr_get_table(net, RT6_TABLE_DFLT);
-	if (!mrt)
+	rcu_read_lock();
+	mrt = __ip6mr_get_table(net, RT6_TABLE_DFLT);
+	if (!mrt) {
+		rcu_read_unlock();
 		return ERR_PTR(-ENOENT);
+	}
 
 	iter->mrt = mrt;
 
-	rcu_read_lock();
 	return mr_vif_seq_start(seq, pos);
 }
 
@@ -2287,11 +2301,13 @@ int ip6mr_get_route(struct net *net, struct sk_buff *skb, struct rtmsg *rtm,
 	struct mfc6_cache *cache;
 	struct rt6_info *rt = dst_rt6_info(skb_dst(skb));
 
-	mrt = ip6mr_get_table(net, RT6_TABLE_DFLT);
-	if (!mrt)
+	rcu_read_lock();
+	mrt = __ip6mr_get_table(net, RT6_TABLE_DFLT);
+	if (!mrt) {
+		rcu_read_unlock();
 		return -ENOENT;
+	}
 
-	rcu_read_lock();
 	cache = ip6mr_cache_find(mrt, &rt->rt6i_src.addr, &rt->rt6i_dst.addr);
 	if (!cache && skb->dev) {
 		int vif = ip6mr_find_vif(mrt, skb->dev);
@@ -2571,7 +2587,7 @@ static int ip6mr_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 		grp = nla_get_in6_addr(tb[RTA_DST]);
 	tableid = nla_get_u32_default(tb[RTA_TABLE], 0);
 
-	mrt = ip6mr_get_table(net, tableid ?: RT_TABLE_DEFAULT);
+	mrt = __ip6mr_get_table(net, tableid ?: RT_TABLE_DEFAULT);
 	if (!mrt) {
 		NL_SET_ERR_MSG_MOD(extack, "MR table does not exist");
 		return -ENOENT;
@@ -2618,7 +2634,7 @@ static int ip6mr_rtm_dumproute(struct sk_buff *skb, struct netlink_callback *cb)
 	if (filter.table_id) {
 		struct mr_table *mrt;
 
-		mrt = ip6mr_get_table(sock_net(skb->sk), filter.table_id);
+		mrt = __ip6mr_get_table(sock_net(skb->sk), filter.table_id);
 		if (!mrt) {
 			if (rtnl_msg_family(cb->nlh) != RTNL_FAMILY_IP6MR)
 				return skb->len;
-- 
2.45.2

[PATCH net 3/3] ipmr: fix tables suspicious RCU usage

[Paolo Abeni]

Similar to the previous patch, plumb the RCU lock inside
the ipmr_get_table(), provided a lockless variant and apply
the latter in the few spots were the lock is already held.

Fixes: 709b46e8d90b ("net: Add compat ioctl support for the ipv4 multicast ioctl SIOCGETSGCNT")
Fixes: f0ad0860d01e ("ipv4: ipmr: support multiple tables")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/ipv4/ipmr.c | 42 +++++++++++++++++++++++++++++-------------
 1 file changed, 29 insertions(+), 13 deletions(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index c6ad01dc8310..7fa31a604723 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -137,7 +137,7 @@ static struct mr_table *ipmr_mr_table_iter(struct net *net,
 	return ret;
 }
 
-static struct mr_table *ipmr_get_table(struct net *net, u32 id)
+static struct mr_table *__ipmr_get_table(struct net *net, u32 id)
 {
 	struct mr_table *mrt;
 
@@ -148,6 +148,16 @@ static struct mr_table *ipmr_get_table(struct net *net, u32 id)
 	return NULL;
 }
 
+static struct mr_table *ipmr_get_table(struct net *net, u32 id)
+{
+	struct mr_table *mrt;
+
+	rcu_read_lock();
+	mrt = __ipmr_get_table(net, id);
+	rcu_read_unlock();
+	return mrt;
+}
+
 static int ipmr_fib_lookup(struct net *net, struct flowi4 *flp4,
 			   struct mr_table **mrt)
 {
@@ -189,7 +199,7 @@ static int ipmr_rule_action(struct fib_rule *rule, struct flowi *flp,
 
 	arg->table = fib_rule_get_table(rule, arg);
 
-	mrt = ipmr_get_table(rule->fr_net, arg->table);
+	mrt = __ipmr_get_table(rule->fr_net, arg->table);
 	if (!mrt)
 		return -EAGAIN;
 	res->mrt = mrt;
@@ -315,6 +325,8 @@ static struct mr_table *ipmr_get_table(struct net *net, u32 id)
 	return net->ipv4.mrt;
 }
 
+#define __ipmr_get_table ipmr_get_table
+
 static int ipmr_fib_lookup(struct net *net, struct flowi4 *flp4,
 			   struct mr_table **mrt)
 {
@@ -408,7 +420,7 @@ static struct mr_table *ipmr_new_table(struct net *net, u32 id)
 	if (id != RT_TABLE_DEFAULT && id >= 1000000000)
 		return ERR_PTR(-EINVAL);
 
-	mrt = ipmr_get_table(net, id);
+	mrt = __ipmr_get_table(net, id);
 	if (mrt)
 		return mrt;
 
@@ -1383,7 +1395,7 @@ int ip_mroute_setsockopt(struct sock *sk, int optname, sockptr_t optval,
 		goto out_unlock;
 	}
 
-	mrt = ipmr_get_table(net, raw_sk(sk)->ipmr_table ? : RT_TABLE_DEFAULT);
+	mrt = __ipmr_get_table(net, raw_sk(sk)->ipmr_table ? : RT_TABLE_DEFAULT);
 	if (!mrt) {
 		ret = -ENOENT;
 		goto out_unlock;
@@ -2271,11 +2283,13 @@ int ipmr_get_route(struct net *net, struct sk_buff *skb,
 	struct mr_table *mrt;
 	int err;
 
-	mrt = ipmr_get_table(net, RT_TABLE_DEFAULT);
-	if (!mrt)
+	rcu_read_lock();
+	mrt = __ipmr_get_table(net, RT_TABLE_DEFAULT);
+	if (!mrt) {
+		rcu_read_unlock();
 		return -ENOENT;
+	}
 
-	rcu_read_lock();
 	cache = ipmr_cache_find(mrt, saddr, daddr);
 	if (!cache && skb->dev) {
 		int vif = ipmr_find_vif(mrt, skb->dev);
@@ -2559,7 +2573,7 @@ static int ipmr_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 	grp = nla_get_in_addr_default(tb[RTA_DST], 0);
 	tableid = nla_get_u32_default(tb[RTA_TABLE], 0);
 
-	mrt = ipmr_get_table(net, tableid ? tableid : RT_TABLE_DEFAULT);
+	mrt = __ipmr_get_table(net, tableid ? tableid : RT_TABLE_DEFAULT);
 	if (!mrt) {
 		err = -ENOENT;
 		goto errout_free;
@@ -2613,7 +2627,7 @@ static int ipmr_rtm_dumproute(struct sk_buff *skb, struct netlink_callback *cb)
 	if (filter.table_id) {
 		struct mr_table *mrt;
 
-		mrt = ipmr_get_table(sock_net(skb->sk), filter.table_id);
+		mrt = __ipmr_get_table(sock_net(skb->sk), filter.table_id);
 		if (!mrt) {
 			if (rtnl_msg_family(cb->nlh) != RTNL_FAMILY_IPMR)
 				return skb->len;
@@ -2721,7 +2735,7 @@ static int rtm_to_ipmr_mfcc(struct net *net, struct nlmsghdr *nlh,
 			break;
 		}
 	}
-	mrt = ipmr_get_table(net, tblid);
+	mrt = __ipmr_get_table(net, tblid);
 	if (!mrt) {
 		ret = -ENOENT;
 		goto out;
@@ -2929,13 +2943,15 @@ static void *ipmr_vif_seq_start(struct seq_file *seq, loff_t *pos)
 	struct net *net = seq_file_net(seq);
 	struct mr_table *mrt;
 
-	mrt = ipmr_get_table(net, RT_TABLE_DEFAULT);
-	if (!mrt)
+	rcu_read_lock();
+	mrt = __ipmr_get_table(net, RT_TABLE_DEFAULT);
+	if (!mrt) {
+		rcu_read_unlock();
 		return ERR_PTR(-ENOENT);
+	}
 
 	iter->mrt = mrt;
 
-	rcu_read_lock();
 	return mr_vif_seq_start(seq, pos);
 }
 
-- 
2.45.2