From 47980b6dbf83961eec1c1363ea986e9c06ff8054 Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Thu, 14 May 2026 14:21:57 +0200 Subject: netfilter: nf_conntrack_gre: fix gre keymap list corruption Quoting reporter: A race between GRE keymap insertion and destruction can corrupt the kernel list or use a freed object. `nf_ct_gre_keymap_add()` publishes a new keymap pointer before the embedded `list_head` is linked, while `nf_ct_gre_keymap_destroy()` can concurrently delete and free that same object. An unprivileged user can reach this through the PPTP conntrack helper by racing PPTP control messages or helper teardown, leading to KASAN-detectable list corruption/UAF in kernel context. ## Root Cause Analysis `exp_gre()` installs GRE expectations for a PPTP control flow and then adds two GRE keymap entries [..] The add path publishes `ct_pptp_info->keymap[dir]` before linking the embedded list node [..] Concurrent teardown deletes that partially initialized object. Make add/destroy symmetric: install both, destroy both while under lock. Furthermore, we should refuse to publish a new mapping in case ct is going away, else we may leak the allocation. The "retrans" detection is strange: existing mapping is checked for key equality with the new mapping, then for "is on the list" via list walk. But I can't see how an existing keymap entry can be NOT on list. Change this to only check if we're asked to map same tuple again -- if so, skip re-install, else signal failure. Last, add a bug trap for the keymap list; it has to be empty when namespace is going away. Reported-by: Leo Lin Signed-off-by: Florian Westphal --- include/linux/netfilter/nf_conntrack_proto_gre.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'include/linux/netfilter') diff --git a/include/linux/netfilter/nf_conntrack_proto_gre.h b/include/linux/netfilter/nf_conntrack_proto_gre.h index 9ee7014400e8..ad5563f0f864 100644 --- a/include/linux/netfilter/nf_conntrack_proto_gre.h +++ b/include/linux/netfilter/nf_conntrack_proto_gre.h @@ -18,9 +18,10 @@ struct nf_ct_gre_keymap { struct rcu_head rcu; }; -/* add new tuple->key_reply pair to keymap */ -int nf_ct_gre_keymap_add(struct nf_conn *ct, enum ip_conntrack_dir dir, - struct nf_conntrack_tuple *t); +/* add tuple->key_reply pairs to keymap */ +bool nf_ct_gre_keymap_add(struct nf_conn *ct, + const struct nf_conntrack_tuple *orig, + const struct nf_conntrack_tuple *repl); /* delete keymap entries */ void nf_ct_gre_keymap_destroy(struct nf_conn *ct); -- cgit v1.2.3 From ec1806a730a1c0b3d68a7f9afe81514fb0dd7991 Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Sat, 25 Apr 2026 15:00:50 +0200 Subject: netfilter: x_tables: disable 32bit compat interface in user namespaces This feature is required to use 32bit arp/ip/ip6/ebtables binaries on 64bit kernels. I don't think there are many users left. Support has been a compile-time option since 2021 and defaults to off since 2023. The XTABLES_COMPAT config option is already off in many distributions including Debian and Fedora. Give a few more months before complete removal but disable support in user namespaces already. Assisted-by: Claude:claude-sonnet-4-6 Signed-off-by: Florian Westphal --- include/linux/netfilter/x_tables.h | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) (limited to 'include/linux/netfilter') diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h index 5a1c5c336fa4..20d70dddbe50 100644 --- a/include/linux/netfilter/x_tables.h +++ b/include/linux/netfilter/x_tables.h @@ -534,4 +534,21 @@ int xt_compat_check_entry_offsets(const void *base, const char *elems, unsigned int next_offset); #endif /* CONFIG_NETFILTER_XTABLES_COMPAT */ + +static inline bool xt_compat_check(void) +{ +#ifdef CONFIG_NETFILTER_XTABLES_COMPAT + if (!in_compat_syscall()) + return true; + + pr_warn_once("%s %s\n", + "xtables 32bit compat interface no longer supported", + "in namespaces and will be removed soon."); + + if (!capable(CAP_NET_ADMIN)) + return false; +#endif + return true; +} + #endif /* _X_TABLES_H */ -- cgit v1.2.3 From 22f9dbed18bcc865d750ed109c6ae2dd4cf2af55 Mon Sep 17 00:00:00 2001 From: Randy Dunlap Date: Sat, 13 Jun 2026 22:25:24 -0700 Subject: netfilter: x_tables.h: fix all kernel-doc warnings - use correct names in kernel-doc comments - add missing struct members to kernel-doc comments Warning: include/linux/netfilter/x_tables.h:41 struct member 'targinfo' not described in 'xt_action_param' Warning: include/linux/netfilter/x_tables.h:41 Excess struct member 'targetinfo' description in 'xt_action_param' Warning: include/linux/netfilter/x_tables.h:90 struct member 'family' not described in 'xt_mtchk_param' Warning: include/linux/netfilter/x_tables.h:90 struct member 'nft_compat' not described in 'xt_mtchk_param' Warning: include/linux/netfilter/x_tables.h:101 expecting prototype for struct xt_mdtor_param. Prototype was for struct xt_mtdtor_param instead Warning: include/linux/netfilter/x_tables.h:121 struct member 'net' not described in 'xt_tgchk_param' Warning: include/linux/netfilter/x_tables.h:121 struct member 'table' not described in 'xt_tgchk_param' Warning: include/linux/netfilter/x_tables.h:121 struct member 'target' not described in 'xt_tgchk_param' Warning: include/linux/netfilter/x_tables.h:121 struct member 'targinfo' not described in 'xt_tgchk_param' Warning: include/linux/netfilter/x_tables.h:121 struct member 'hook_mask' not described in 'xt_tgchk_param' Warning: include/linux/netfilter/x_tables.h:121 struct member 'family' not described in 'xt_tgchk_param' Warning: include/linux/netfilter/x_tables.h:121 struct member 'nft_compat' not described in 'xt_tgchk_param' Warning: include/linux/netfilter/x_tables.h:345 expecting prototype for xt_recseq(). Prototype was for DECLARE_PER_CPU() instead Signed-off-by: Randy Dunlap Signed-off-by: Pablo Neira Ayuso --- include/linux/netfilter/x_tables.h | 29 +++++++++++++++++++++-------- 1 file changed, 21 insertions(+), 8 deletions(-) (limited to 'include/linux/netfilter') diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h index 20d70dddbe50..25062f4a0dd5 100644 --- a/include/linux/netfilter/x_tables.h +++ b/include/linux/netfilter/x_tables.h @@ -18,7 +18,7 @@ * @match: the match extension * @target: the target extension * @matchinfo: per-match data - * @targetinfo: per-target data + * @targinfo: per-target data * @state: pointer to hook state this packet came from * @fragoff: packet is a fragment, this is the data offset * @thoff: position of transport header relative to skb->data @@ -77,7 +77,9 @@ static inline u_int8_t xt_family(const struct xt_action_param *par) * @match: struct xt_match through which this function was invoked * @matchinfo: per-match data * @hook_mask: via which hooks the new rule is reachable - * Other fields as above. + * @family: actual NFPROTO_* through which the function is invoked + * (helpful when match->family == NFPROTO_UNSPEC) + * @nft_compat: running from the nft compat layer if true */ struct xt_mtchk_param { struct net *net; @@ -91,8 +93,13 @@ struct xt_mtchk_param { }; /** - * struct xt_mdtor_param - match destructor parameters - * Fields as above. + * struct xt_mtdtor_param - match destructor parameters + * + * @net: network namespace through which the check was invoked + * @match: struct xt_match through which this function was invoked + * @matchinfo: per-match data + * @family: actual NFPROTO_* through which the function is invoked + * (helpful when match->family == NFPROTO_UNSPEC) */ struct xt_mtdtor_param { struct net *net; @@ -105,10 +112,16 @@ struct xt_mtdtor_param { * struct xt_tgchk_param - parameters for target extensions' * checkentry functions * + * @net: network namespace through which the check was invoked + * @table: table the rule is tried to be inserted into * @entryinfo: the family-specific rule data * (struct ipt_entry, ip6t_entry, arpt_entry, ebt_entry) - * - * Other fields see above. + * @target: the target extension + * @targinfo: per-target data + * @hook_mask: via which hooks the new rule is reachable + * @family: actual NFPROTO_* through which the function is invoked + * (helpful when match->family == NFPROTO_UNSPEC) + * @nft_compat: running from the nft compat layer if true */ struct xt_tgchk_param { struct net *net; @@ -336,9 +349,9 @@ struct xt_table_info *xt_alloc_table_info(unsigned int size); void xt_free_table_info(struct xt_table_info *info); /** - * xt_recseq - recursive seqcount for netfilter use + * var xt_recseq - recursive seqcount for netfilter use * - * Packet processing changes the seqcount only if no recursion happened + * Packet processing changes the seqcount only if no recursion happened. * get_counters() can use read_seqcount_begin()/read_seqcount_retry(), * because we use the normal seqcount convention : * Low order bit set to 1 if a writer is active. -- cgit v1.2.3