From owner-freebsd-bugs@freebsd.org Thu Jul 20 15:16:11 2017 Return-Path: Delivered-To: freebsd-bugs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id E19E7C7A295 for ; Thu, 20 Jul 2017 15:16:11 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org (kenobi.freebsd.org [IPv6:2001:1900:2254:206a::16:76]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id AAF3F6CFFA for ; Thu, 20 Jul 2017 15:16:11 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from bugs.freebsd.org ([127.0.1.118]) by kenobi.freebsd.org (8.15.2/8.15.2) with ESMTP id v6KFGBNZ066761 for ; Thu, 20 Jul 2017 15:16:11 GMT (envelope-from bugzilla-noreply@freebsd.org) From: bugzilla-noreply@freebsd.org To: freebsd-bugs@FreeBSD.org Subject: [Bug 220882] m_move_pkthdr leaves m_nextpkt 'dangling' Date: Thu, 20 Jul 2017 15:16:11 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: CURRENT X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Some People X-Bugzilla-Who: fodillemlinkarim@gmail.com X-Bugzilla-Status: New X-Bugzilla-Resolution: X-Bugzilla-Priority: --- X-Bugzilla-Assigned-To: freebsd-bugs@FreeBSD.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: bug_id short_desc product version rep_platform op_sys bug_status bug_severity priority component assigned_to reporter Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugs.freebsd.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: freebsd-bugs@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 20 Jul 2017 15:16:12 -0000 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D220882 Bug ID: 220882 Summary: m_move_pkthdr leaves m_nextpkt 'dangling' Product: Base System Version: CURRENT Hardware: Any OS: Any Status: New Severity: Affects Some People Priority: --- Component: kern Assignee: freebsd-bugs@FreeBSD.org Reporter: fodillemlinkarim@gmail.com Hi, As many of you know, when dealing with IP fragments the kernel will build a list of packets (fragments) chained together through the m_nextpkt pointer. This is all good until someone tries to do a M_PREPEND on one of the packet= in the chain and the M_PREPEND has to create an extra mbuf to prepend at the beginning of the chain. When doing so m_move_pkthdr is called to copy the current PKTHDR fields (ta= gs and flags) to the mbuf that was prepended. The function also does: to->m_pkthdr =3D from->m_pkthdr; This, for the case I am interested in, essentially leaves the 'from' mbuf w= ith a dangling pointer m_nextpkt pointing to the next fragment. While this is mostly harmless because only mbufs of pkthdr types are supposed to have m_nextpkt it triggers some panics when running with INVARIANTS in NetGraph = (see ng_base.c :: CHECK_DATA_MBUF(m)): ... if (n->m_nextpkt !=3D NULL) \ panic("%s: m_nextpkt", __func__); \ } ... So I would like to propose the following patch: @@ -442,10 +442,11 @@ m_move_pkthdr(struct mbuf *to, struct mbuf *from) if ((to->m_flags & M_EXT) =3D=3D 0) to->m_data =3D to->m_pktdat; to->m_pkthdr =3D from->m_pkthdr; /* especially tags */ SLIST_INIT(&from->m_pkthdr.tags); /* purge tags from src */ from->m_flags &=3D ~M_PKTHDR; + from->m_nextpkt =3D NULL; } It will reset the m_nextpkt so we don't have two mbufs pointing to the same next packet. This is fairly harmless and solves a problem for us here at XipLink. Best regards, Karim. --=20 You are receiving this mail because: You are the assignee for the bug.=