netfilter: nfnetlink: Fix for interrupted hook dumps

Handling of concurrent hook changes with a dump in progress was
problematic in nfnl_hook_dump and entirely broken in nfnl_hook_dump_nat.
Address all issues in a single patch to please the review LLM.

Introduce sequence numbers in struct netns_nf to replace pointer
value-based modification detection which may fail due to memory buffer
reuse. This also eliminates the need for most manual cb->seq updates and
excessive array index value checks.

Since nat hook updates are protected by a different mutex than others,
they have to bump their own sequence number. nfnl_hook_dump_nat
therefore open-codes what nl_dump_check_consistent does but bumps
cb->seq instead of setting NLM_F_DUMP_INTR flag.

Dumps of many nat hooks was entirely broken since the array index was
not (re)stored. Use cb->args[1] for that and make sure it is reset upon
completion as the same dump may loop over multiple arrays of nat hooks.

In nfnl_hook_dump, don't signal NLM_F_DUMP_INTR if
nfnl_hook_entries_head returns error: This is a permanent condition
which does not change during a dump. It is already caught by
nfnl_hook_dump_start though, so should not happen anyway.

In general, access ops array pointer values using READ_ONCE since they
are assigned to using WRITE_ONCE.

Avoid setting NLM_F_DUMP_INTR flag in garbage memory by calling
nl_dump_check_consistent only for non-empty skbs. If not a single
netlink message was created, nfnetlink code will take care of setting
the flag.

Fixes: e2cf17d3774c ("netfilter: add new hook nfnl subsystem")
Fixes: b010e2a4a9ac ("netfilter: nfnetlink_hook: Dump nat type chains")
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/net/netns/netfilter.h b/include/net/netns/netfilter.h
index a6a0bf4a247e..7fd78394d1e7 100644
--- a/include/net/netns/netfilter.h
+++ b/include/net/netns/netfilter.h
@@ -33,5 +33,7 @@ struct netns_nf {
 #if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
 	unsigned int defrag_ipv6_users;
 #endif
+	unsigned int hook_base_seq;
+	unsigned int nat_hook_base_seq;
 };
 #endif