From 58416c6786fa972314cb699a7df28d8c09268f03 Mon Sep 17 00:00:00 2001
From: Xiao Wang <jasowang@redhat.com>
Date: Mon, 30 Jul 2018 06:31:57 +0200
Subject: [PATCH 8/8] slirp: correct size computation while concatenating mbuf

RH-Author: Xiao Wang <jasowang@redhat.com>
Message-id: <1532932317-6100-3-git-send-email-jasowang@redhat.com>
Patchwork-id: 81543
O-Subject: [RHEL7.6/7.5.z qemu-kvm PATCH 2/2] slirp: correct size computation while concatenating mbuf
Bugzilla: 1586248
RH-Acked-by: wexu@redhat.com
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>

From: Prasad J Pandit <pjp@fedoraproject.org>

Upstream: 70f2e64e4dde slirp: Convert mbufs to use g_malloc() and g_free()
Notes: Conflict since we lacks 70f2e64e4dde
       ("slirp: Convert mbufs to use g_malloc() and g_free()")

While reassembling incoming fragmented datagrams, 'm_cat' routine
extends the 'mbuf' buffer, if it has insufficient room. It computes
a wrong buffer size, which leads to overwriting adjacent heap buffer
area. Correct this size computation in m_cat.

Reported-by: ZDI Disclosures <zdi-disclosures@trendmicro.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 slirp/mbuf.c | 11 +++++------
 slirp/mbuf.h |  8 +++-----
 2 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/slirp/mbuf.c b/slirp/mbuf.c
index 5565fd1..ced2033 100644
--- a/slirp/mbuf.c
+++ b/slirp/mbuf.c
@@ -139,7 +139,7 @@ m_cat(struct mbuf *m, struct mbuf *n)
 	 * If there's no room, realloc
 	 */
 	if (M_FREEROOM(m) < n->m_len)
-		m_inc(m,m->m_size+MINCSIZE);
+		m_inc(m, m->m_len + n->m_len);
 
 	memcpy(m->m_data+m->m_len, n->m_data, n->m_len);
 	m->m_len += n->m_len;
@@ -148,7 +148,7 @@ m_cat(struct mbuf *m, struct mbuf *n)
 }
 
 
-/* make m size bytes large */
+/* make m 'size' bytes large from m_data */
 void
 m_inc(struct mbuf *m, int size)
 {
@@ -159,12 +159,12 @@ m_inc(struct mbuf *m, int size)
 
         if (m->m_flags & M_EXT) {
 	  datasize = m->m_data - m->m_ext;
-	  m->m_ext = (char *)realloc(m->m_ext,size);
+	  m->m_ext = (char *)realloc(m->m_ext, size + datasize);
 	  m->m_data = m->m_ext + datasize;
         } else {
 	  char *dat;
 	  datasize = m->m_data - m->m_dat;
-	  dat = (char *)malloc(size);
+	  dat = (char *)malloc(size + datasize);
 	  memcpy(dat, m->m_dat, m->m_size);
 
 	  m->m_ext = dat;
@@ -172,8 +172,7 @@ m_inc(struct mbuf *m, int size)
 	  m->m_flags |= M_EXT;
         }
 
-        m->m_size = size;
-
+        m->m_size = size + datasize;
 }
 
 
diff --git a/slirp/mbuf.h b/slirp/mbuf.h
index b144f1c..32e5120 100644
--- a/slirp/mbuf.h
+++ b/slirp/mbuf.h
@@ -33,8 +33,6 @@
 #ifndef _MBUF_H_
 #define _MBUF_H_
 
-#define MINCSIZE 4096	/* Amount to increase mbuf if too small */
-
 /*
  * Macros for type conversion
  * mtod(m,t) -	convert mbuf pointer to data pointer of correct type
@@ -72,11 +70,11 @@ struct mbuf {
 	struct	mbuf *m_prevpkt;	/* Flags aren't used in the output queue */
 	int	m_flags;		/* Misc flags */
 
-	int	m_size;			/* Size of data */
+	int	m_size;			/* Size of mbuf, from m_dat or m_ext */
 	struct	socket *m_so;
 
-	caddr_t	m_data;			/* Location of data */
-	int	m_len;			/* Amount of data in this mbuf */
+	caddr_t	m_data;			/* Current location of data */
+	int	m_len;			/* Amount of data in this mbuf, from m_data */
 
 	Slirp *slirp;
 	bool	arp_requested;
-- 
1.8.3.1