From 24f90fa3994b992d1a09003a3db2599330a5232a Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Tue, 17 Mar 2026 12:23:08 +0100 Subject: netfilter: bpf: defer hook memory release until rcu readers are done 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 --- net/netfilter/nf_bpf_link.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'net') diff --git a/net/netfilter/nf_bpf_link.c b/net/netfilter/nf_bpf_link.c index 6f3a6411f4af..c20031891b86 100644 --- a/net/netfilter/nf_bpf_link.c +++ b/net/netfilter/nf_bpf_link.c @@ -170,7 +170,7 @@ static int bpf_nf_link_update(struct bpf_link *link, struct bpf_prog *new_prog, static const struct bpf_link_ops bpf_nf_link_lops = { .release = bpf_nf_link_release, - .dealloc = bpf_nf_link_dealloc, + .dealloc_deferred = bpf_nf_link_dealloc, .detach = bpf_nf_link_detach, .show_fdinfo = bpf_nf_link_show_info, .fill_link_info = bpf_nf_link_fill_link_info, -- cgit v1.2.3 From d73f4b53aaaea4c95f245e491aa5eeb8a21874ce Mon Sep 17 00:00:00 2001 From: Pablo Neira Ayuso Date: Tue, 17 Mar 2026 20:00:26 +0100 Subject: netfilter: nf_tables: release flowtable after rcu grace period on error 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 --- net/netfilter/nf_tables_api.c | 1 + 1 file changed, 1 insertion(+) (limited to 'net') diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c index 9b1c8d0a35fb..3922cff1bb3d 100644 --- a/net/netfilter/nf_tables_api.c +++ b/net/netfilter/nf_tables_api.c @@ -9203,6 +9203,7 @@ static int nf_tables_newflowtable(struct sk_buff *skb, return 0; err_flowtable_hooks: + synchronize_rcu(); nft_trans_destroy(trans); err_flowtable_trans: nft_hooks_destroy(&flowtable->hook_list); -- cgit v1.2.3 From dbdfaae9609629a9569362e3b8f33d0a20fd783c Mon Sep 17 00:00:00 2001 From: Weiming Shi Date: Thu, 19 Mar 2026 15:32:44 +0800 Subject: nfnetlink_osf: validate individual option lengths in fingerprints 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 --- net/netfilter/nfnetlink_osf.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'net') diff --git a/net/netfilter/nfnetlink_osf.c b/net/netfilter/nfnetlink_osf.c index 94e3eac5743a..45d9ad231a92 100644 --- a/net/netfilter/nfnetlink_osf.c +++ b/net/netfilter/nfnetlink_osf.c @@ -302,7 +302,9 @@ static int nfnl_osf_add_callback(struct sk_buff *skb, { struct nf_osf_user_finger *f; struct nf_osf_finger *kf = NULL, *sf; + unsigned int tot_opt_len = 0; int err = 0; + int i; if (!capable(CAP_NET_ADMIN)) return -EPERM; @@ -318,6 +320,17 @@ static int nfnl_osf_add_callback(struct sk_buff *skb, if (f->opt_num > ARRAY_SIZE(f->opt)) return -EINVAL; + for (i = 0; i < f->opt_num; i++) { + if (!f->opt[i].length || f->opt[i].length > MAX_IPOPTLEN) + return -EINVAL; + if (f->opt[i].kind == OSFOPT_MSS && f->opt[i].length < 4) + return -EINVAL; + + tot_opt_len += f->opt[i].length; + if (tot_opt_len > MAX_IPOPTLEN) + return -EINVAL; + } + if (!memchr(f->genre, 0, MAXGENRELEN) || !memchr(f->subtype, 0, MAXGENRELEN) || !memchr(f->version, 0, MAXGENRELEN)) -- cgit v1.2.3