netkit-telnetd: Fix buffer overflow in netoprintf

netoprintf() was not handling a case where
return value of vsnprintf is greater than
"size"(2nd argument), results in buffer overflow
while adjusting "nfrontp" pointer to point
beyond "netobuf" buffer.

Here is one such case where "nfrontp"
crossed boundaries of "netobuf", and
pointing to another global variable.

(gdb) p &netobuf[8255]
$5 = 0x55c93afe8b1f <netobuf+8255> ""
(gdb) p nfrontp
$6 = 0x55c93afe8c20 <terminaltype> "\377"
(gdb) p &terminaltype
$7 = (char **) 0x55c93afe8c20 <terminaltype>
(gdb)

This resulted in crash of telnetd service
with segmentation fault.

Signed-off-by: Julius Hemanth Pitti <jpitti@cisco.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>
(cherry picked from commit 232b82afd405c526f822294509e1d32388544ed4)
[appears to be CVE-2020-10188]
Signed-off-by: Armin Kuster <akuster808@gmail.com>

2 files changed, 57 insertions, 0 deletions

diff --git a/meta-networking/recipes-netkit/netkit-telnet/files/0001-telnetd-utility.c-Fix-buffer-overflow-in-netoprintf.patch b/meta-networking/recipes-netkit/netkit-telnet/files/0001-telnetd-utility.c-Fix-buffer-overflow-in-netoprintf.patch
new file mode 100644
index 0000000000..8f983e40ab
--- /dev/null
+++ b/meta-networking/recipes-netkit/netkit-telnet/files/0001-telnetd-utility.c-Fix-buffer-overflow-in-netoprintf.patch
@@ -0,0 +1,56 @@
+From 9c81c8e5bc7782e8ae12c078615abc3c896059f2 Mon Sep 17 00:00:00 2001
+From: Julius Hemanth Pitti <jpitti@cisco.com>
+Date: Tue, 14 Jul 2020 22:34:19 -0700
+Subject: [PATCH] telnetd/utility.c: Fix buffer overflow in netoprintf
+
+As per man page of vsnprintf, when formated
+string size is greater than "size"(2nd argument),
+then vsnprintf returns size of formated string,
+not "size"(2nd argument).
+
+netoprintf() was not handling a case where
+return value of vsnprintf is greater than
+"size"(2nd argument), results in buffer overflow
+while adjusting "nfrontp" pointer to point
+beyond "netobuf" buffer.
+
+Here is one such case where "nfrontp"
+crossed boundaries of "netobuf", and
+pointing to another global variable.
+
+(gdb) p &netobuf[8255]
+$5 = 0x55c93afe8b1f <netobuf+8255> ""
+(gdb) p nfrontp
+$6 = 0x55c93afe8c20 <terminaltype> "\377"
+(gdb) p &terminaltype
+$7 = (char **) 0x55c93afe8c20 <terminaltype>
+(gdb)
+
+This resulted in crash of telnetd service
+with segmentation fault.
+
+Though this is DoS security bug, I couldn't
+find any CVE ID for this.
+
+Upstream-Status: Pending
+
+Signed-off-by: Julius Hemanth Pitti <jpitti@cisco.com>
+---
+ telnetd/utility.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/telnetd/utility.c b/telnetd/utility.c
+index b9a46a6..4811f14 100644
+--- a/telnetd/utility.c
++++ b/telnetd/utility.c
+@@ -66,7 +66,7 @@ netoprintf(const char *fmt, ...)
+       len = vsnprintf(nfrontp, maxsize, fmt, ap);
+       va_end(ap);
+ 
+-      if (len<0 || len==maxsize) {
++      if (len<0 || len>=maxsize) {
+         /* didn't fit */
+         netflush();
+       }
+--
+2.19.1
diff --git a/meta-networking/recipes-netkit/netkit-telnet/netkit-telnet_0.17.bb b/meta-networking/recipes-netkit/netkit-telnet/netkit-telnet_0.17.bb
index 0e92add633..08dd532b62 100644
--- a/meta-networking/recipes-netkit/netkit-telnet/netkit-telnet_0.17.bb
+++ b/meta-networking/recipes-netkit/netkit-telnet/netkit-telnet_0.17.bb
@@ -13,6 +13,7 @@ SRC_URI = "http://ftp.linux.org.uk/pub/linux/Networking/netkit/${BP}.tar.gz \
            file://0001-telnet-telnetd-Fix-print-format-strings.patch \
            file://0001-telnet-telnetd-Fix-deadlock-on-cleanup.patch \
            file://CVE-2020-10188.patch \
+           file://0001-telnetd-utility.c-Fix-buffer-overflow-in-netoprintf.patch \
            "
 
 UPSTREAM_CHECK_URI = "${DEBIAN_MIRROR}/main/n/netkit-telnet/"