[PATCH net v3 1/1] ipmr: account multicast table and route memory

A netadmin in a user+net namespace can create many IPv6 multicast
routing tables with MRT6_TABLE. Each unseen id allocates an mr_table,
links it into mr6_tables, and leaves it until netns teardown. Those
objects were not charged to memcg, so the host unreclaimable slab
grows with the table count.

Account mr_table allocations with GFP_KERNEL_ACCOUNT and mark the
IPv4/IPv6 MFC caches SLAB_ACCOUNT. This matches the established
handling of IP addresses, routes and alternate interface names.

The first unaccounted IPv6 heap table appeared in commit 4e16880cb422
("netns: ip6mr: dynamically allocates vif6_table"), which replaced a
static vif6_table[] with kcalloc(..., GFP_KERNEL). Commit
6bd521433942 ("ipv6: ip6mr: move mroute data into seperate structure")
only wrapped that already-heap state into mr6_table. Commit
d1db275dd3f6 ("ipv6: ip6mr: support multiple tables") only expanded
the table count from 1 to N. IPv6 MFC entries were already unaccounted
from commit 7bc570c8b4f7 ("[IPV6] MROUTE: Support multicast
forwarding."); IPv4 ip_mrt_cache is older still.

Fixes: 4e16880cb422 ("netns: ip6mr: dynamically allocates vif6_table")
Cc: stable@vger.kernel.org
Reported-by: Vega <redacted>
Assisted-by: LLM
Signed-off-by: Zihan Xi <redacted>
---
changes in v3:
  - Drop the table lifetime / unpublished-alloc / empty-reclaim
    approach from v2.
  - Charge mr_table allocations with GFP_KERNEL_ACCOUNT and mark the
    IPv4/IPv6 MFC caches SLAB_ACCOUNT, as suggested by Ido Schimmel.
  - Point Fixes: at 4e16880cb422, the first GFP_KERNEL IPv6 heap
    vif6_table. 6bd521433942 only wrapped that already-heap state;
    d1db275dd3f6 only expanded the table count from 1 to N.
  - Cover: unfixed evidence is Slab/SUnreclaim growth with RET:0, not
    a host OOM. The memcg OOM log is from the patched kernel under
    64M memory.max using poc.static.
  - v2 Link:
    https://lore.kernel.org/all/cover.1788622674.git.zihanx@nebusec.ai/ (local)
changes in v2:
  - Drop the shared mr_table refcount / list_del_rcu path that broke
    the ipmr forwarding selftest.
  - Limit the v2 approach to net/ipv6/ip6mr.c.
  - v1 Link:
    https://lore.kernel.org/all/cover.1784795838.git.zihanx@nebusec.ai/ (local)

 net/ipv4/ipmr.c      | 3 ++-
 net/ipv4/ipmr_base.c | 2 +-
 net/ipv6/ip6mr.c     | 2 +-
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index e5f2b1c6150d2..b9c544d48c452 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c

@@ -3376,7 +3376,8 @@ int __init ip_mr_init(void)
 {
 	int err;
 
-	mrt_cachep = KMEM_CACHE(mfc_cache, SLAB_HWCACHE_ALIGN | SLAB_PANIC);
+	mrt_cachep = KMEM_CACHE(mfc_cache,
+				SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
 
 	err = register_pernet_subsys(&ipmr_net_ops);
 	if (err)

diff --git a/net/ipv4/ipmr_base.c b/net/ipv4/ipmr_base.c
index 867b24beded11..a0ec6d19a237f 100644
--- a/net/ipv4/ipmr_base.c
+++ b/net/ipv4/ipmr_base.c

@@ -52,7 +52,7 @@ mr_table_alloc(struct net *net, u32 id,
 	struct mr_table *mrt;
 	int err;
 
-	mrt = kzalloc_obj(*mrt);
+	mrt = kzalloc_obj(*mrt, GFP_KERNEL_ACCOUNT);
 	if (!mrt)
 		return ERR_PTR(-ENOMEM);
 	mrt->id = id;

diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 3f2ed9b77deb5..9d8116b5edb17 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c

@@ -1427,7 +1427,7 @@ int __init ip6_mr_init(void)
 {
 	int err;
 
-	mrt_cachep = KMEM_CACHE(mfc6_cache, SLAB_HWCACHE_ALIGN);
+	mrt_cachep = KMEM_CACHE(mfc6_cache, SLAB_HWCACHE_ALIGN | SLAB_ACCOUNT);
 	if (!mrt_cachep)
 		return -ENOMEM;
 

base-commit: 641d03105cc0d2437e32fdeec164f91a4ccef6c4
-- 
2.43.0