kernel/linux.git/net/netfilter, branch master

netfilter: nfnetlink_osf: fix potential NULL dereference in ttl check

2026-04-20T21:45:44+00:00

The nf_osf_ttl() function accessed skb->dev to perform a local interface address lookup without verifying that the device pointer was valid. Additionally, the implementation utilized an in_dev_for_each_ifa_rcu loop to match the packet source address against local interface addresses. It assumed that packets from the same subnet should not see a decrement on the initial TTL. A packet might appear it is from the same subnet but it actually isn't especially in modern environments with containers and virtual switching. Remove the device dereference and interface loop. Replace the logic with a switch statement that evaluates the TTL according to the ttl_check. Fixes: 11eeef41d5f6 ("netfilter: passive OS fingerprint xtables match") Reported-by: Kito Xu (veritas501) Closes: https://lore.kernel.org/netfilter-devel/20260414074556.2512750-1-hxzene@gmail.com/ Signed-off-by: Fernando Fernandez Mancera Reviewed-by: Pablo Neira Ayuso Signed-off-by: Pablo Neira Ayuso

netfilter: nfnetlink_osf: fix out-of-bounds read on option matching

2026-04-20T21:45:43+00:00

In nf_osf_match(), the nf_osf_hdr_ctx structure is initialized once and passed by reference to nf_osf_match_one() for each fingerprint checked. During TCP option parsing, nf_osf_match_one() advances the shared ctx->optp pointer. If a fingerprint perfectly matches, the function returns early without restoring ctx->optp to its initial state. If the user has configured NF_OSF_LOGLEVEL_ALL, the loop continues to the next fingerprint. However, because ctx->optp was not restored, the next call to nf_osf_match_one() starts parsing from the end of the options buffer. This causes subsequent matches to read garbage data and fail immediately, making it impossible to log more than one match or logging incorrect matches. Instead of using a shared ctx->optp pointer, pass the context as a constant pointer and use a local pointer (optp) for TCP option traversal. This makes nf_osf_match_one() strictly stateless from the caller's perspective, ensuring every fingerprint check starts at the correct option offset. Fixes: 1a6a0951fc00 ("netfilter: nfnetlink_osf: add missing fmatch check") Suggested-by: Florian Westphal Signed-off-by: Fernando Fernandez Mancera Reviewed-by: Pablo Neira Ayuso Signed-off-by: Pablo Neira Ayuso

ipvs: fix MTU check for GSO packets in tunnel mode

2026-04-20T21:45:43+00:00

Currently, IPVS skips MTU checks for GSO packets by excluding them with the !skb_is_gso(skb) condition. This creates problems when IPVS tunnel mode encapsulates GSO packets with IPIP headers. The issue manifests in two ways: 1. MTU violation after encapsulation: When a GSO packet passes through IPVS tunnel mode, the original MTU check is bypassed. After adding the IPIP tunnel header, the packet size may exceed the outgoing interface MTU, leading to unexpected fragmentation at the IP layer. 2. Fragmentation with problematic IP IDs: When net.ipv4.vs.pmtu_disc=1 and a GSO packet with multiple segments is fragmented after encapsulation, each segment gets a sequentially incremented IP ID (0, 1, 2, ...). This happens because: a) The GSO packet bypasses MTU check and gets encapsulated b) At __ip_finish_output, the oversized GSO packet is split into separate SKBs (one per segment), with IP IDs incrementing c) Each SKB is then fragmented again based on the actual MTU This sequential IP ID allocation differs from the expected behavior and can cause issues with fragment reassembly and packet tracking. Fix this by properly validating GSO packets using skb_gso_validate_network_len(). This function correctly validates whether the GSO segments will fit within the MTU after segmentation. If validation fails, send an ICMP Fragmentation Needed message to enable proper PMTU discovery. Fixes: 4cdd34084d53 ("netfilter: nf_conntrack_ipv6: improve fragmentation handling") Signed-off-by: Yingnan Zhang <342144303@qq.com> Acked-by: Julian Anastasov Signed-off-by: Pablo Neira Ayuso

netfilter: nat: use kfree_rcu to release ops

2026-04-20T21:45:41+00:00

Florian Westphal says: "Historically this is not an issue, even for normal base hooks: the data path doesn't use the original nf_hook_ops that are used to register the callbacks. However, in v5.14 I added the ability to dump the active netfilter hooks from userspace. This code will peek back into the nf_hook_ops that are available at the tail of the pointer-array blob used by the datapath. The nat hooks are special, because they are called indirectly from the central nat dispatcher hook. They are currently invisible to the nfnl hook dump subsystem though. But once that changes the nat ops structures have to be deferred too." Update nf_nat_register_fn() to deal with partial exposition of the hooks from error path which can be also an issue for nfnetlink_hook. Fixes: e2cf17d3774c ("netfilter: add new hook nfnl subsystem") Signed-off-by: Pablo Neira Ayuso

netfilter: xtables: restrict several matches to inet family

2026-04-20T21:27:52+00:00

This is a partial revert of: commit ab4f21e6fb1c ("netfilter: xtables: use NFPROTO_UNSPEC in more extensions") to allow ipv4 and ipv6 only. - xt_mac - xt_owner - xt_physdev These extensions are not used by ebtables in userspace. Moreover, xt_realm is only for ipv4, since dst->tclassid is ipv4 specific. Fixes: ab4f21e6fb1c ("netfilter: xtables: use NFPROTO_UNSPEC in more extensions") Reported-by: "Kito Xu (veritas501)" Signed-off-by: Pablo Neira Ayuso

netfilter: conntrack: remove sprintf usage

2026-04-20T21:27:46+00:00

Replace it with scnprintf, the buffer sizes are expected to be large enough to hold the result, no need for snprintf+overflow check. Increase buffer size in mangle_content_len() while at it. BUG: KASAN: stack-out-of-bounds in vsnprintf+0xea5/0x1270 Write of size 1 at addr [..] vsnprintf+0xea5/0x1270 sprintf+0xb1/0xe0 mangle_content_len+0x1ac/0x280 nf_nat_sdp_session+0x1cc/0x240 process_sdp+0x8f8/0xb80 process_invite_request+0x108/0x2b0 process_sip_msg+0x5da/0xf50 sip_help_tcp+0x45e/0x780 nf_confirm+0x34d/0x990 [..] Fixes: 9fafcd7b2032 ("[NETFILTER]: nf_conntrack/nf_nat: add SIP helper port") Reported-by: Yiming Qian Signed-off-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso

netfilter: nfnetlink_osf: fix divide-by-zero in OSF_WSS_MODULO

2026-04-20T21:27:41+00:00

nf_osf_match_one() computes ctx->window % f->wss.val in the OSF_WSS_MODULO branch with no guard for f->wss.val == 0. A CAP_NET_ADMIN user can add such a fingerprint via nfnetlink; a subsequent matching TCP SYN divides by zero and panics the kernel. Reject the bogus fingerprint in nfnl_osf_add_callback() above the per-option for-loop. f->wss is per-fingerprint, not per-option, so the check must run regardless of f->opt_num (including 0). Also reject wss.wc >= OSF_WSS_MAX; nf_osf_match_one() already treats that as "should not happen". Crash: Oops: divide error: 0000 [#1] SMP KASAN NOPTI RIP: 0010:nf_osf_match_one (net/netfilter/nfnetlink_osf.c:98) Call Trace: nf_osf_match (net/netfilter/nfnetlink_osf.c:220) xt_osf_match_packet (net/netfilter/xt_osf.c:32) ipt_do_table (net/ipv4/netfilter/ip_tables.c:348) nf_hook_slow (net/netfilter/core.c:622) ip_local_deliver (net/ipv4/ip_input.c:265) ip_rcv (include/linux/skbuff.h:1162) __netif_receive_skb_one_core (net/core/dev.c:6181) process_backlog (net/core/dev.c:6642) __napi_poll (net/core/dev.c:7710) net_rx_action (net/core/dev.c:7945) handle_softirqs (kernel/softirq.c:622) Fixes: 11eeef41d5f6 ("netfilter: passive OS fingerprint xtables match") Reported-by: Weiming Shi Suggested-by: Florian Westphal Suggested-by: Pablo Neira Ayuso Signed-off-by: Xiang Mei Reviewed-by: Fernando Fernandez Mancera Signed-off-by: Pablo Neira Ayuso

netfilter: nft_osf: restrict it to ipv4

2026-04-20T21:27:36+00:00

This expression only supports for ipv4, restrict it. Fixes: b96af92d6eaf ("netfilter: nf_tables: implement Passive OS fingerprint module in nft_osf") Acked-by: Florian Westphal Reviewed-by: Fernando Fernandez Mancera Signed-off-by: Pablo Neira Ayuso

netfilter: require Ethernet MAC header before using eth_hdr()

2026-04-10T10:16:27+00:00

`ip6t_eui64`, `xt_mac`, the `bitmap:ip,mac`, `hash:ip,mac`, and `hash:mac` ipset types, and `nf_log_syslog` access `eth_hdr(skb)` after either assuming that the skb is associated with an Ethernet device or checking only that the `ETH_HLEN` bytes at `skb_mac_header(skb)` lie between `skb->head` and `skb->data`. Make these paths first verify that the skb is associated with an Ethernet device, that the MAC header was set, and that it spans at least a full Ethernet header before accessing `eth_hdr(skb)`. Suggested-by: Florian Westphal Tested-by: Ren Wei Signed-off-by: Zhengchuan Liang Signed-off-by: Ren Wei Signed-off-by: Florian Westphal

netfilter: nft_fwd_netdev: check ttl/hl before forwarding

2026-04-10T10:16:27+00:00

Drop packets if their ttl/hl is too small for forwarding. Fixes: d32de98ea70f ("netfilter: nft_fwd_netdev: allow to forward packets via neighbour layer") Signed-off-by: Florian Westphal