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Fri, 10 Apr 2026 03:16:53 -0700 (PDT) Received: from localhost ([196.207.164.177]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43d63deb904sm6848506f8f.9.2026.04.10.03.16.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Apr 2026 03:16:52 -0700 (PDT) Date: Fri, 10 Apr 2026 13:16:49 +0300 From: Dan Carpenter To: Jiayuan Chen Cc: Simon Horman , netdev@vger.kernel.org Subject: [bug report] xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path Message-ID: Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Hello Jiayuan Chen, Commit 81b84de32bb2 ("xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path") from Feb 6, 2026 (linux-next), leads to the following Smatch static checker warning: net/ipv4/icmp.c:587 icmp_route_lookup() error: we previously assumed 'rt2' could be null (see line 576) net/ipv4/icmp.c 491 static struct rtable *icmp_route_lookup(struct net *net, struct flowi4 *fl4, 492 struct sk_buff *skb_in, 493 const struct iphdr *iph, __be32 saddr, 494 dscp_t dscp, u32 mark, int type, 495 int code, struct icmp_bxm *param) 496 { 497 struct net_device *route_lookup_dev; 498 struct dst_entry *dst, *dst2; 499 struct rtable *rt, *rt2; 500 struct flowi4 fl4_dec; 501 int err; 502 503 memset(fl4, 0, sizeof(*fl4)); 504 fl4->daddr = (param->replyopts.opt.srr ? 505 param->replyopts.opt.faddr : iph->saddr); 506 fl4->saddr = saddr; 507 fl4->flowi4_mark = mark; 508 fl4->flowi4_uid = sock_net_uid(net, NULL); 509 fl4->flowi4_dscp = dscp; 510 fl4->flowi4_proto = IPPROTO_ICMP; 511 fl4->fl4_icmp_type = type; 512 fl4->fl4_icmp_code = code; 513 route_lookup_dev = icmp_get_route_lookup_dev(skb_in); 514 fl4->flowi4_oif = l3mdev_master_ifindex(route_lookup_dev); 515 516 security_skb_classify_flow(skb_in, flowi4_to_flowi_common(fl4)); 517 rt = ip_route_output_key_hash(net, fl4, skb_in); 518 if (IS_ERR(rt)) 519 return rt; 520 521 /* No need to clone since we're just using its address. */ 522 rt2 = rt; 523 524 dst = xfrm_lookup(net, &rt->dst, 525 flowi4_to_flowi(fl4), NULL, 0); 526 rt = dst_rtable(dst); 527 if (!IS_ERR(dst)) { 528 if (rt != rt2) 529 return rt; 530 if (inet_addr_type_dev_table(net, route_lookup_dev, 531 fl4->daddr) == RTN_LOCAL) 532 return rt; 533 } else if (PTR_ERR(dst) == -EPERM) { 534 rt = NULL; 535 } else { 536 return rt; 537 } 538 err = xfrm_decode_session_reverse(net, skb_in, flowi4_to_flowi(&fl4_dec), AF_INET); 539 if (err) 540 goto relookup_failed; 541 542 if (inet_addr_type_dev_table(net, route_lookup_dev, 543 fl4_dec.saddr) == RTN_LOCAL) { 544 rt2 = __ip_route_output_key(net, &fl4_dec); 545 if (IS_ERR(rt2)) 546 err = PTR_ERR(rt2); 547 } else { 548 struct flowi4 fl4_2 = {}; 549 unsigned long orefdst; 550 551 fl4_2.daddr = fl4_dec.saddr; 552 rt2 = ip_route_output_key(net, &fl4_2); 553 if (IS_ERR(rt2)) { 554 err = PTR_ERR(rt2); 555 goto relookup_failed; 556 } 557 /* Ugh! */ 558 orefdst = skb_dstref_steal(skb_in); 559 err = ip_route_input(skb_in, fl4_dec.daddr, fl4_dec.saddr, 560 dscp, rt2->dst.dev) ? -EINVAL : 0; 561 562 dst_release(&rt2->dst); 563 rt2 = skb_rtable(skb_in); 564 /* steal dst entry from skb_in, don't drop refcnt */ 565 skb_dstref_steal(skb_in); 566 skb_dstref_restore(skb_in, orefdst); 567 568 /* 569 * At this point, fl4_dec.daddr should NOT be local (we 570 * checked fl4_dec.saddr above). However, a race condition 571 * may occur if the address is added to the interface 572 * concurrently. In that case, ip_route_input() returns a 573 * LOCAL route with dst.output=ip_rt_bug, which must not 574 * be used for output. 575 */ 576 if (!err && rt2 && rt2->rt_type == RTN_LOCAL) { ^^^ Can rt2 really be NULL here? 577 net_warn_ratelimited("detected local route for %pI4 during ICMP sending, src %pI4\n", 578 &fl4_dec.daddr, &fl4_dec.saddr); 579 dst_release(&rt2->dst); 580 err = -EINVAL; 581 } 582 } 583 584 if (err) 585 goto relookup_failed; 586 --> 587 dst2 = xfrm_lookup(net, &rt2->dst, flowi4_to_flowi(&fl4_dec), NULL, ^^^^^^^^^ Because, if so, then we are screwed here. 588 XFRM_LOOKUP_ICMP); 589 rt2 = dst_rtable(dst2); 590 if (!IS_ERR(dst2)) { 591 dst_release(&rt->dst); 592 rt = rt2; 593 } else if (PTR_ERR(dst2) == -EPERM) { 594 if (rt) 595 dst_release(&rt->dst); 596 return rt2; 597 } else { 598 err = PTR_ERR(dst2); 599 goto relookup_failed; 600 } 601 return rt; 602 603 relookup_failed: 604 if (rt) 605 return rt; 606 return ERR_PTR(err); 607 } This email is a free service from the Smatch-CI project [smatch.sf.net]. regards, dan carpenter