untrusted comment: signature from openbsd 5.6 base private key
RWR0EANmo9nqhpu5mEMdLuZ056ynwx+qvxaVbodk7LsWqC0UCch3P2Ll0uGzfyJl/FSN9KH7tQgwwjbPwyss35EQNAlUAULiYgU=

OpenBSD 5.6 errata 15, Jan 8, 2015

Fix CVE-2014-6272 in libevent 1.4 event buffer handling.  OpenBSD
base uses it for the programs: cu tmux ftp-proxy httpd ldapd relayd
tftp-proxy tftpd

A defect in the Libevent evbuffer API leaves some programs that
pass insanely large inputs to evbuffers open to a possible heap
overflow or infinite loop.

Apply patch using:

   signify -Vep /etc/signify/openbsd-56-base.pub -x 015_libevent.patch.sig \
       -m - | (cd /usr/src && patch -p0)

Then build and install libevent

   cd /usr/src/lib/libevent
   make obj
   make
   make install


Index: lib/libevent/buffer.c
===================================================================
RCS file: /mount/cvsdev/cvs/openbsd/src/lib/libevent/buffer.c,v
retrieving revision 1.19
diff -u -p -r1.19 buffer.c
--- lib/libevent/buffer.c       17 Jul 2010 17:16:47 -0000      1.19
+++ lib/libevent/buffer.c       7 Jan 2015 19:11:19 -0000
@@ -53,6 +53,7 @@

#include <assert.h>
#include <errno.h>
+#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
@@ -145,7 +146,8 @@ evbuffer_add_vprintf(struct evbuffer *bu
       va_list aq;

       /* make sure that at least some space is available */
-       evbuffer_expand(buf, 64);
+       if (evbuffer_expand(buf, 64) < 0)
+               return (-1);
       for (;;) {
               size_t used = buf->misalign + buf->off;
               buffer = (char *)buf->buffer + buf->off;
@@ -351,26 +353,38 @@ evbuffer_align(struct evbuffer *buf)
int
evbuffer_expand(struct evbuffer *buf, size_t datlen)
{
-       size_t need = buf->misalign + buf->off + datlen;
+       size_t used = buf->misalign + buf->off;
+
+       assert(buf->totallen >= used);

       /* If we can fit all the data, then we don't have to do anything */
-       if (buf->totallen >= need)
+       if (buf->totallen - used >= datlen)
               return (0);
+       /* If we would need to overflow to fit this much data, we can't
+        * do anything. */
+       if (datlen > SIZE_MAX - buf->off)
+               return (-1);

       /*
        * If the misalignment fulfills our data needs, we just force an
        * alignment to happen.  Afterwards, we have enough space.
        */
-       if (buf->misalign >= datlen) {
+       if (buf->totallen - buf->off >= datlen) {
               evbuffer_align(buf);
       } else {
               void *newbuf;
               size_t length = buf->totallen;
+               size_t need = buf->off + datlen;

               if (length < 256)
                       length = 256;
-               while (length < need)
-                       length <<= 1;
+               if (need < SIZE_MAX / 2) {
+                       while (length < need) {
+                               length <<= 1;
+                       }
+               } else {
+                       length = need;
+               }

               if (buf->orig_buffer != buf->buffer)
                       evbuffer_align(buf);
@@ -387,10 +401,10 @@ evbuffer_expand(struct evbuffer *buf, si
int
evbuffer_add(struct evbuffer *buf, const void *data, size_t datlen)
{
-       size_t need = buf->misalign + buf->off + datlen;
+       size_t used = buf->misalign + buf->off;
       size_t oldoff = buf->off;

-       if (buf->totallen < need) {
+       if (buf->totallen - used < datlen) {
               if (evbuffer_expand(buf, datlen) == -1)
                       return (-1);
       }