File CVE-2021-3592-3594-3595-qemut-prereq1.patch of Package xen.26348

Subject: slirp: Add sanity check for str option length
From: Fam Zheng famz@redhat.com Fri Sep 14 15:26:15 2018 +0800
Date: Thu Mar 21 15:47:26 2019 -0500:
Git: 70b8acfa0d496ccc796ab183581c98fd8574163e

When user provides a long domainname or hostname that doesn't fit in the
DHCP packet, we mustn't overflow the response packet buffer. Instead,
report errors, following the g_warning() in the slirp->vdnssearch
branch.

Also check the strlen against 256 when initializing slirp, which limit
is also from the protocol where one byte represents the string length.
This gives an early error before the warning which is harder to notice
or diagnose.

Reported-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Fam Zheng <famz@redhat.com>
Tested-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
(cherry picked from commit 6e157a0339793bb081705f52318fc77afd10addf)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

Index: xen-4.7.6-testing/tools/qemu-xen-traditional-dir-remote/net.c
===================================================================
--- xen-4.7.6-testing.orig/tools/qemu-xen-traditional-dir-remote/net.c
+++ xen-4.7.6-testing/tools/qemu-xen-traditional-dir-remote/net.c
@@ -1709,7 +1709,11 @@ int net_client_init(const char *device,
     if (!strcmp(device, "user")) {
         if (get_param_value(buf, sizeof(buf), "hostname", p)) {
             pstrcpy(slirp_hostname, sizeof(slirp_hostname), buf);
-        }
+            if (slirp_hostname && strlen(slirp_hostname) > 255) {
+                fprintf(stderr, "'vhostname' parameter cannot exceed 255 bytes\n"); 
+                return -1;
+            }
+       }
         if (get_param_value(buf, sizeof(buf), "restrict", p)) {
             slirp_restrict = (buf[0] == 'y') ? 1 : 0;
         }
Index: xen-4.7.6-testing/tools/qemu-xen-traditional-dir-remote/slirp/bootp.c
===================================================================
--- xen-4.7.6-testing.orig/tools/qemu-xen-traditional-dir-remote/slirp/bootp.c
+++ xen-4.7.6-testing/tools/qemu-xen-traditional-dir-remote/slirp/bootp.c
@@ -136,6 +136,7 @@ static void bootp_reply(struct bootp_t *
     struct in_addr dns_addr;
     int dhcp_msg_type, val;
     uint8_t *q;
+    uint8_t *end;
 
     /* extract exact DHCP msg type */
     dhcp_decode(bp->bp_vend, DHCP_OPT_LEN, &dhcp_msg_type);
@@ -197,6 +198,7 @@ static void bootp_reply(struct bootp_t *
     daddr.sin_addr.s_addr = 0xffffffffu;
 
     q = rbp->bp_vend;
+    end = (uint8_t *)&rbp[1];
     memcpy(q, rfc1533_cookie, 4);
     q += 4;
 
@@ -245,12 +247,17 @@ static void bootp_reply(struct bootp_t *
 
         if (*slirp_hostname) {
             val = strlen(slirp_hostname);
-            *q++ = RFC1533_HOSTNAME;
-            *q++ = val;
-            memcpy(q, slirp_hostname, val);
-            q += val;
+            if (q + val + 2 >= end) {
+                dprintf("DHCP packet size exceeded, omitting host name option.");
+            } else {
+                *q++ = RFC1533_HOSTNAME;
+                *q++ = val;
+                memcpy(q, slirp_hostname, val);
+                q += val;
+            }
         }
     }
+    assert(q < end);
     *q++ = RFC1533_END;
 
     m->m_len = sizeof(struct bootp_t) -