kernel/net/netfilter, branch master

nfnetlink_osf: validate individual option lengths in fingerprints

2026-03-19T09:27:07Z

nfnl_osf_add_callback() validates opt_num bounds and string NUL-termination but does not check individual option length fields. A zero-length option causes nf_osf_match_one() to enter the option matching loop even when foptsize sums to zero, which matches packets with no TCP options where ctx->optp is NULL: Oops: general protection fault KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] RIP: 0010:nf_osf_match_one (net/netfilter/nfnetlink_osf.c:98) Call Trace: nf_osf_match (net/netfilter/nfnetlink_osf.c:227) xt_osf_match_packet (net/netfilter/xt_osf.c:32) ipt_do_table (net/ipv4/netfilter/ip_tables.c:293) nf_hook_slow (net/netfilter/core.c:623) ip_local_deliver (net/ipv4/ip_input.c:262) ip_rcv (net/ipv4/ip_input.c:573) Additionally, an MSS option (kind=2) with length < 4 causes out-of-bounds reads when nf_osf_match_one() unconditionally accesses optp[2] and optp[3] for MSS value extraction. While RFC 9293 section 3.2 specifies that the MSS option is always exactly 4 bytes (Kind=2, Length=4), the check uses "< 4" rather than "!= 4" because lengths greater than 4 do not cause memory safety issues -- the buffer is guaranteed to be at least foptsize bytes by the ctx->optsize == foptsize check. Reject fingerprints where any option has zero length, or where an MSS option has length less than 4, at add time rather than trusting these values in the packet matching hot path. Fixes: 11eeef41d5f6 ("netfilter: passive OS fingerprint xtables match") Reported-by: Xiang Mei Signed-off-by: Weiming Shi Signed-off-by: Florian Westphal

netfilter: nf_tables: release flowtable after rcu grace period on error

2026-03-19T09:26:31Z

Call synchronize_rcu() after unregistering the hooks from error path, since a hook that already refers to this flowtable can be already registered, exposing this flowtable to packet path and nfnetlink_hook control plane. This error path is rare, it should only happen by reaching the maximum number hooks or by failing to set up to hardware offload, just call synchronize_rcu(). There is a check for already used device hooks by different flowtable that could result in EEXIST at this late stage. The hook parser can be updated to perform this check earlier to this error path really becomes rarely exercised. Uncovered by KASAN reported as use-after-free from nfnetlink_hook path when dumping hooks. Fixes: 3b49e2e94e6e ("netfilter: nf_tables: add flow table netlink frontend") Reported-by: Yiming Qian Signed-off-by: Pablo Neira Ayuso Signed-off-by: Florian Westphal

netfilter: bpf: defer hook memory release until rcu readers are done

2026-03-19T09:26:31Z

Yiming Qian reports UaF when concurrent process is dumping hooks via nfnetlink_hooks: BUG: KASAN: slab-use-after-free in nfnl_hook_dump_one.isra.0+0xe71/0x10f0 Read of size 8 at addr ffff888003edbf88 by task poc/79 Call Trace: nfnl_hook_dump_one.isra.0+0xe71/0x10f0 netlink_dump+0x554/0x12b0 nfnl_hook_get+0x176/0x230 [..] Defer release until after concurrent readers have completed. Reported-by: Yiming Qian Fixes: 84601d6ee68a ("bpf: add bpf_link support for BPF_NETFILTER programs") Signed-off-by: Florian Westphal

netfilter: nf_conntrack_h323: check for zero length in DecodeQ931()

2026-03-13T14:31:15Z

In DecodeQ931(), the UserUserIE code path reads a 16-bit length from the packet, then decrements it by 1 to skip the protocol discriminator byte before passing it to DecodeH323_UserInformation(). If the encoded length is 0, the decrement wraps to -1, which is then passed as a large value to the decoder, leading to an out-of-bounds read. Add a check to ensure len is positive after the decrement. Fixes: 5e35941d9901 ("[NETFILTER]: Add H.323 conntrack/NAT helper") Reported-by: Klaudia Kloc Reported-by: Dawid Moczadło Tested-by: Jenny Guanni Qu Signed-off-by: Jenny Guanni Qu Signed-off-by: Florian Westphal

netfilter: xt_time: use unsigned int for monthday bit shift

2026-03-13T14:31:15Z

The monthday field can be up to 31, and shifting a signed integer 1 by 31 positions (1 << 31) is undefined behavior in C, as the result overflows a 32-bit signed int. Use 1U to ensure well-defined behavior for all valid monthday values. Change the weekday shift to 1U as well for consistency. Fixes: ee4411a1b1e0 ("[NETFILTER]: x_tables: add xt_time match") Reported-by: Klaudia Kloc Reported-by: Dawid Moczadło Tested-by: Jenny Guanni Qu Signed-off-by: Jenny Guanni Qu Signed-off-by: Florian Westphal

netfilter: xt_CT: drop pending enqueued packets on template removal

2026-03-13T14:31:15Z

Templates refer to objects that can go away while packets are sitting in nfqueue refer to: - helper, this can be an issue on module removal. - timeout policy, nfnetlink_cttimeout might remove it. The use of templates with zone and event cache filter are safe, since this just copies values. Flush these enqueued packets in case the template rule gets removed. Fixes: 24de58f46516 ("netfilter: xt_CT: allow to attach timeout policy + glue code") Reported-by: Yiming Qian Signed-off-by: Pablo Neira Ayuso Signed-off-by: Florian Westphal

netfilter: nft_ct: drop pending enqueued packets on removal

2026-03-13T14:31:15Z

Packets sitting in nfqueue might hold a reference to: - templates that specify the conntrack zone, because a percpu area is used and module removal is possible. - conntrack timeout policies and helper, where object removal leave a stale reference. Since these objects can just go away, drop enqueued packets to avoid stale reference to them. If there is a need for finer grain removal, this logic can be revisited to make selective packet drop upon dependencies. Fixes: 7e0b2b57f01d ("netfilter: nft_ct: add ct timeout support") Reported-by: Yiming Qian Signed-off-by: Pablo Neira Ayuso Signed-off-by: Florian Westphal

nf_tables: nft_dynset: fix possible stateful expression memleak in error path

2026-03-13T14:31:15Z

If cloning the second stateful expression in the element via GFP_ATOMIC fails, then the first stateful expression remains in place without being released. unreferenced object (percpu) 0x607b97e9cab8 (size 16): comm "softirq", pid 0, jiffies 4294931867 hex dump (first 16 bytes on cpu 3): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 backtrace (crc 0): pcpu_alloc_noprof+0x453/0xd80 nft_counter_clone+0x9c/0x190 [nf_tables] nft_expr_clone+0x8f/0x1b0 [nf_tables] nft_dynset_new+0x2cb/0x5f0 [nf_tables] nft_rhash_update+0x236/0x11c0 [nf_tables] nft_dynset_eval+0x11f/0x670 [nf_tables] nft_do_chain+0x253/0x1700 [nf_tables] nft_do_chain_ipv4+0x18d/0x270 [nf_tables] nf_hook_slow+0xaa/0x1e0 ip_local_deliver+0x209/0x330 Fixes: 563125a73ac3 ("netfilter: nftables: generalize set extension to support for several expressions") Reported-by: Gurpreet Shergill Signed-off-by: Pablo Neira Ayuso Signed-off-by: Florian Westphal

netfilter: nf_conntrack_h323: fix OOB read in decode_int() CONS case

2026-03-13T14:31:15Z

In decode_int(), the CONS case calls get_bits(bs, 2) to read a length value, then calls get_uint(bs, len) without checking that len bytes remain in the buffer. The existing boundary check only validates the 2 bits for get_bits(), not the subsequent 1-4 bytes that get_uint() reads. This allows a malformed H.323/RAS packet to cause a 1-4 byte slab-out-of-bounds read. Add a boundary check for len bytes after get_bits() and before get_uint(). Fixes: 5e35941d9901 ("[NETFILTER]: Add H.323 conntrack/NAT helper") Reported-by: Klaudia Kloc Reported-by: Dawid Moczadło Signed-off-by: Jenny Guanni Qu Signed-off-by: Florian Westphal

netfilter: nf_flow_table_ip: reset mac header before vlan push

2026-03-13T14:31:15Z

With double vlan tagged packets in the fastpath, getting the error: skb_vlan_push got skb with skb->data not at mac header (offset 18) Call skb_reset_mac_header() before calling skb_vlan_push(). Fixes: c653d5a78f34 ("netfilter: flowtable: inline vlan encapsulation in xmit path") Signed-off-by: Eric Woudstra Acked-by: Pablo Neira Ayuso Signed-off-by: Florian Westphal