untrusted comment: signature from openbsd 5.6 base private key
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OpenBSD 5.6 errata 28, Jul 26, 2015:

A kernel memory leak could be triggered by an unprivileged user in
a failure case when using execve under systrace.

Apply by doing:
   signify -Vep /etc/signify/openbsd-56-base.pub -x 028_execve.patch.sig \
       -m - | (cd /usr/src && patch -p0)

And then rebuild and install a new kernel:
   cd /usr/src/sys/arch/`machine`/conf
   KK=`sysctl -n kern.osversion | cut -d# -f1`
   config $KK
   cd ../compile/$KK
   make
   make install

Index: sys/kern/kern_exec.c
===================================================================
RCS file: /data/src/openbsd/src/sys/kern/kern_exec.c,v
retrieving revision 1.144.4.1
diff -u -p -r1.144.4.1 kern_exec.c
--- sys/kern/kern_exec.c        19 Oct 2014 22:18:02 -0000      1.144.4.1
+++ sys/kern/kern_exec.c        26 Jul 2015 23:15:42 -0000
@@ -763,12 +763,12 @@ exec_abort:

free_pack_abort:
       free(pack.ep_hdr, M_EXEC, 0);
+       if (pathbuf != NULL)
+               pool_put(&namei_pool, pathbuf);
       exit1(p, W_EXITCODE(0, SIGABRT), EXIT_NORMAL);

       /* NOTREACHED */
       atomic_clearbits_int(&pr->ps_flags, PS_INEXEC);
-       if (pathbuf != NULL)
-               pool_put(&namei_pool, pathbuf);

       return (0);
}