ASAN and dhcpcd with privilege separation

[Roy Marples <roy%marples.name@localhost>]

Hi List

I'm strugging to get dhcpcd to debug a deliberate leak with either gcc or clang 
ASAN.

Disable ASLR:
sysctl -w security.pax.aslr.enabled=0

Compiling src/external/bsd/dhcpcd/sbin/dhcpcd like so:
CFLAGS=-fsanitize=address LDFLAGS=-fsanitize=address make

Apply this patch:
diff -r 7ea0253a7567 external/bsd/dhcpcd/dist/src/dhcpcd.c
--- a/external/bsd/dhcpcd/dist/src/dhcpcd.c     Fri Jan 29 07:58:57 2021 +0000
+++ b/external/bsd/dhcpcd/dist/src/dhcpcd.c     Sun Jan 31 02:50:23 2021 +0000
@@ -2614,7 +2614,7 @@
 #ifdef PRIVSEP
        eloop_free(ctx.ps_eloop);
 #endif
-       eloop_free(ctx.eloop);
+       //eloop_free(ctx.eloop);
        if (ctx.script != dhcpcd_default_script)
                free(ctx.script);
        if (ctx.options & DHCPCD_STARTED && !(ctx.options & DHCPCD_FORKED))


Test dhcpcd:
obj.amd64/dhcpcd -x
obj.amd64/dhcpcd -dB
wait a few moments
CTRL-C
No error reported

Disable SUID, chroot and resource limits. IE, just the privilege separation code 
active but everything runs root:
diff -r 7ea0253a7567 external/bsd/dhcpcd/dist/src/privsep.c
--- a/external/bsd/dhcpcd/dist/src/privsep.c    Fri Jan 29 07:58:57 2021 +0000
+++ b/external/bsd/dhcpcd/dist/src/privsep.c    Sun Jan 31 02:50:23 2021 +0000
@@ -114,6 +114,8 @@
 static int
 ps_dropprivs(struct dhcpcd_ctx *ctx)
 {
+return 0;
+
        struct passwd *pw = ctx->ps_user;

        if (ctx->options & DHCPCD_LAUNCHER)

Test again, still no error.
Disable the privsep code entirely, dhcpcd will run as a single process:
diff -r 7ea0253a7567 external/bsd/dhcpcd/dist/src/dhcpcd.c
--- a/external/bsd/dhcpcd/dist/src/dhcpcd.c     Fri Jan 29 07:58:57 2021 +0000
+++ b/external/bsd/dhcpcd/dist/src/dhcpcd.c     Sun Jan 31 02:50:23 2021 +0000
@@ -2160,7 +2160,7 @@
 #endif

 #ifdef PRIVSEP
-       ps_init(&ctx);
+       //ps_init(&ctx);
 #endif

 #ifndef SMALL

Now we get errors!
dhcpcd does not use threading at all, it's all many single processes.
Why does this not work for dhcpcd privilege separation? Anyone have an idea on 
how to resolve this?

Please reply direct to me as well as I'm not subbed to this list.

Thanks

Roy