From: claudio <claudio@openbsd.org>
Date: Wed, 21 Feb 2024 09:28:29 +0000 (+0000)
Subject: Keep mbuf data alignment intact in m_defrag()
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=e78015d9dc23483d48e25ae60e7d5425eb967bf2;p=openbsd

Keep mbuf data alignment intact in m_defrag()

The recent TSO support in em(4) triggered an alignment error on the TCP
header. In em(4) m_defrag() is called before setting up the TSO dma bits
and with that the TCP header was suddenly no longer aligned. Like other
mbuf functions preserve the data alignment in m_defrag() to prevent such
unaligned packets.

With help and OK bluhm@ mglocker@
---

diff --git a/sys/kern/uipc_mbuf.c b/sys/kern/uipc_mbuf.c
index 5d1f9a7b802..ec675a2333f 100644
--- a/sys/kern/uipc_mbuf.c
+++ b/sys/kern/uipc_mbuf.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uipc_mbuf.c,v 1.288 2023/10/20 16:25:15 bluhm Exp $	*/
+/*	$OpenBSD: uipc_mbuf.c,v 1.289 2024/02/21 09:28:29 claudio Exp $	*/
 /*	$NetBSD: uipc_mbuf.c,v 1.15.4.1 1996/06/13 17:11:44 cgd Exp $	*/
 
 /*
@@ -550,21 +550,24 @@ int
 m_defrag(struct mbuf *m, int how)
 {
 	struct mbuf *m0;
+	unsigned int adj;
 
 	if (m->m_next == NULL)
 		return (0);
 
 	KASSERT(m->m_flags & M_PKTHDR);
 
+	adj = mtod(m, unsigned long) & (sizeof(long) - 1);
 	if ((m0 = m_gethdr(how, m->m_type)) == NULL)
 		return (ENOBUFS);
-	if (m->m_pkthdr.len > MHLEN) {
-		MCLGETL(m0, how, m->m_pkthdr.len);
+	if (m->m_pkthdr.len + adj > MHLEN) {
+		MCLGETL(m0, how, m->m_pkthdr.len + adj);
 		if (!(m0->m_flags & M_EXT)) {
 			m_free(m0);
 			return (ENOBUFS);
 		}
 	}
+	m0->m_data += adj;
 	m_copydata(m, 0, m->m_pkthdr.len, mtod(m0, caddr_t));
 	m0->m_pkthdr.len = m0->m_len = m->m_pkthdr.len;
 
@@ -583,9 +586,9 @@ m_defrag(struct mbuf *m, int how)
 		memcpy(&m->m_ext, &m0->m_ext, sizeof(struct mbuf_ext));
 		MCLINITREFERENCE(m);
 		m->m_flags |= m0->m_flags & (M_EXT|M_EXTWR);
-		m->m_data = m->m_ext.ext_buf;
+		m->m_data = m->m_ext.ext_buf + adj;
 	} else {
-		m->m_data = m->m_pktdat;
+		m->m_data = m->m_pktdat + adj;
 		memcpy(m->m_data, m0->m_data, m0->m_len);
 	}
 	m->m_pkthdr.len = m->m_len = m0->m_len;