Date: Wed, 30 Jul 2025 19:17:22 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 288558] icmp does not reset the fragment offset field when it is going to reply an ICMP packet Message-ID: <bug-288558-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=288558 Bug ID: 288558 Summary: icmp does not reset the fragment offset field when it is going to reply an ICMP packet Product: Base System Version: 13.5-RELEASE Hardware: Any OS: Any Status: New Severity: Affects Only Me Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: jiahali@blackberry.com Created attachment 262567 --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=262567&action=edit Proposed change to fix the issue When ICMP module is going to reply an ICMP packet, icmp_reflect(), it would inherit the ipv4 header of the RX ICMP packet firstly then change the related field at the ipv4 header accordingly. But the IPv4 flags field used to store fragmentation info is not changed. If a DF, don't fragmentation, is set at a RX ICMP packet, the ICMP Reply packet would keep the DF bit set. The ICMP reply packet would be dropped at sys/netinet/ip_output.c::ip_output() if the ICMP reply packet is larger than the network interface's MTU. /* Balk when DF bit is set or the interface didn't support TSO. */ if ((ip_off & IP_DF) || (m->m_pkthdr.csum_flags & (CSUM_TSO | CSUM_INNER_TSO))) { error = EMSGSIZE; IPSTAT_INC(ips_cantfrag); goto bad; } /* * Too large for interface; fragment if possible. If successful, * on return, m will point to a list of packets to be sent. */ error = ip_fragment(ip, &m, mtu, ifp->if_hwassist); Setting Test interface's MTU as 1460 and host interface's MTU as 1500 My Host is Linux, and I can see PINGs fail when using $ ping -I enp0s31f6 192.168.1.129 -s 1472 -c 3 PING 192.168.1.129 (192.168.1.129) from 192.168.1.2 enp0s31f6: 1472(1500) bytes of data. ^C --- 192.168.1.129 ping statistics --- 3 packets transmitted, 0 received, 100% packet loss, time 2046ms -- You are receiving this mail because: You are the assignee for the bug.home | help
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