File 0398-libslirp-slirp-Add-sanity-check-for.patch of Package qemu.29142

From: Jose R Ziviani <jose.ziviani@suse.com>
Date: Tue, 6 Jul 2021 19:51:56 -0600
Subject: libslirp: slirp: Add sanity check for str option length

Git commit: 6fd057f7960bc7b3a69f3c53de5c9d0d5d34a79c
References: bsc#1187364, CVE-2021-3592

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>
Signed-off-by: Jose R Ziviani <jose.ziviani@suse.com>
---
 slirp/bootp.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/slirp/bootp.c b/slirp/bootp.c
index f0508d90d1dc6381b308d4c8308d..69ebe5735568c094aa3c32317d2d 100644
--- a/slirp/bootp.c
+++ b/slirp/bootp.c
@@ -159,6 +159,7 @@ static void bootp_reply(Slirp *slirp, const struct bootp_t *bp)
     struct in_addr preq_addr;
     int dhcp_msg_type, val;
     uint8_t *q;
+    uint8_t *end;
     uint8_t client_ethaddr[ETH_ALEN];
 
     /* extract exact DHCP msg type */
@@ -240,6 +241,7 @@ static void bootp_reply(Slirp *slirp, const struct bootp_t *bp)
     rbp->bp_siaddr = saddr.sin_addr; /* Server IP address */
 
     q = rbp->bp_vend;
+    end = (uint8_t *)&rbp[1];
     memcpy(q, rfc1533_cookie, 4);
     q += 4;
 
@@ -292,16 +294,20 @@ static void bootp_reply(Slirp *slirp, const struct bootp_t *bp)
 
         if (*slirp->client_hostname) {
             val = strlen(slirp->client_hostname);
-            *q++ = RFC1533_HOSTNAME;
-            *q++ = val;
-            memcpy(q, slirp->client_hostname, val);
-            q += val;
+            if (q + val + 2 >= end) {
+                g_warning("DHCP packet size exceeded, "
+                          "omitting host name option.");
+            } else {
+                *q++ = RFC1533_HOSTNAME;
+                *q++ = val;
+                memcpy(q, slirp->client_hostname, val);
+                q += val;
+            }
         }
 
         if (slirp->vdnssearch) {
-            size_t spaceleft = sizeof(rbp->bp_vend) - (q - rbp->bp_vend);
             val = slirp->vdnssearch_len;
-            if (val + 1 > spaceleft) {
+            if (q + val >= end) {
                 g_warning("DHCP packet size exceeded, "
                     "omitting domain-search option.");
             } else {
@@ -323,6 +329,7 @@ static void bootp_reply(Slirp *slirp, const struct bootp_t *bp)
         memcpy(q, nak_msg, sizeof(nak_msg) - 1);
         q += sizeof(nak_msg) - 1;
     }
+    assert(q < end);
     *q = RFC1533_END;
 
     daddr.sin_addr.s_addr = 0xffffffffu;