Commit 3bb398d925 ("netfilter: nf_ct_helper: disable automatic helper assignment") is causing behavior regressions in firewalls, as traffic handled by conntrack helpers is now by default not passed through even though it was before due to missing CT targets (which were not necessary before this commit). The default had to be switched off due to security reasons [1] [2] and therefore should stay the way it is, but let's be friendly to firewall admins and issue a warning the first time we're in situation where packet would be likely passed through with the old default but we're likely going to drop it on the floor now. Rewrite the code a little bit as suggested by Linus, so that we avoid spaghettiing the code even more -- namely the whole decision making process regarding helper selection (either automatic or not) is being separated, so that the whole logic can be simplified and code (condition) duplication reduced. [1] https://cansecwest.com/csw12/conntrack-attack.pdf [2] https://home.regit.org/netfilter-en/secure-use-of-helpers/
Unified · Split
| @@ -188,6 +188,26 @@ nf_ct_helper_ext_add(struct nf_conn *ct, · 187 unmodified lines | ||
| 188 | 188 | } |
| 189 | 189 | EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add); |
| 190 | 190 | |
| 191 | +static struct nf_conntrack_helper * | |
| 192 | +nf_ct_lookup_helper(struct nf_conn *ct, struct net *net) | |
| 193 | +{ | |
| 194 | + if (!net->ct.sysctl_auto_assign_helper) { | |
| 195 | + if (net->ct.auto_assign_helper_warned) | |
| 196 | + return NULL; | |
| 197 | + if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple)) | |
| 198 | + return NULL; | |
| 199 | + pr_info("nf_conntrack: default automatic helper assignment " | |
| 200 | + "has been turned off for security reasons and CT-based " | |
| 201 | + " firewall rule not found. Use the iptables CT target " | |
| 202 | + "to attach helpers instead.\n"); | |
| 203 | + net->ct.auto_assign_helper_warned = 1; | |
| 204 | + return NULL; | |
| 205 | + } | |
| 206 | + | |
| 207 | + return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple); | |
| 208 | +} | |
| 209 | + | |
| 210 | + | |
| 191 | 211 | int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl, |
| 192 | 212 | gfp_t flags) |
| 193 | 213 | { |
| @@ -213,21 +233,14 @@ int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl, · 19 unmodified lines | ||
| 213 | 233 | } |
| 214 | 234 | |
| 215 | 235 | help = nfct_help(ct); |
| 216 | − if (net->ct.sysctl_auto_assign_helper && helper == NULL) { | |
| 217 | − helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple); | |
| 218 | − if (unlikely(!net->ct.auto_assign_helper_warned && helper)) { | |
| 219 | − pr_info("nf_conntrack: automatic helper " | |
| 220 | − "assignment is deprecated and it will " | |
| 221 | − "be removed soon. Use the iptables CT target " | |
| 222 | − "to attach helpers instead.\n"); | |
| 223 | − net->ct.auto_assign_helper_warned = true; | |
| 224 | − } | |
| 225 | − } | |
| 226 | 236 | |
| 227 | 237 | if (helper == NULL) { |
| 228 | − if (help) | |
| 229 | − RCU_INIT_POINTER(help->helper, NULL); | |
| 230 | − return 0; | |
| 238 | + helper = nf_ct_lookup_helper(ct, net); | |
| 239 | + if (helper == NULL) { | |
| 240 | + if (help) | |
| 241 | + RCU_INIT_POINTER(help->helper, NULL); | |
| 242 | + return 0; | |
| 243 | + } | |
| 231 | 244 | } |
| 232 | 245 | |
| 233 | 246 | if (help == NULL) { |