The OSF_WSS_MODULO branch in nf_osf_match_one() performs: ctx->window % f->wss.val without guarding against f->wss.val == 0. A user with CAP_NET_ADMIN can add an OSF fingerprint with wss.wc = OSF_WSS_MODULO and wss.val = 0 via nfnetlink. When a matching TCP SYN packet arrives, the kernel executes a division by zero and panics. The OSF_WSS_PLAIN case already treats val == 0 as a wildcard (match everything). Apply the same semantics to OSF_WSS_MODULO: if val is 0, any window value matches rather than dividing by zero. 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 (discriminator 6)) 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 (discriminator 1)) 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 (.include/linux/skbuff.h:2502 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: 31a9c29210e2 ("netfilter: nf_osf: add struct nf_osf_hdr_ctx") Reported-by: Weiming Shi Signed-off-by: Xiang Mei --- net/netfilter/nfnetlink_osf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/netfilter/nfnetlink_osf.c b/net/netfilter/nfnetlink_osf.c index 45d9ad231..193436aa9 100644 --- a/net/netfilter/nfnetlink_osf.c +++ b/net/netfilter/nfnetlink_osf.c @@ -150,7 +150,7 @@ static bool nf_osf_match_one(const struct sk_buff *skb, fmatch = FMATCH_OK; break; case OSF_WSS_MODULO: - if ((ctx->window % f->wss.val) == 0) + if (f->wss.val == 0 || (ctx->window % f->wss.val) == 0) fmatch = FMATCH_OK; break; } -- 2.43.0