dhcpcd-discuss

Hi,

This patch fixes a segfault in handle_interface: if we're adding an interface
that we already know about (in particular due to a udev event), then calling
init_state/start_interface on ifp is bad because we later free ifp. This leads
to messages like:

  dhcpcd[1342]: eth0: IAID conflicts with one assigned to eth0

and then a crash:

  Invalid read of size 8
    at 0x41CD07: dhcp_handlepacket (dhcp.c:2555)
    by 0x408A74: eloop_start (eloop.c:399)
    by 0x4073B6: main (dhcpcd.c:1537)

  Address 0x54573d8 is 200 bytes inside a block of size 232 free'd
    at 0x4C27507: free (in
/nix/store/jafbjc2y6izmh3sk78fl65n55jll4mj8-valgrind-3.9.0/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
    by 0x40F0A8: free_interface (net.c:153)
    by 0x405443: handle_interface (dhcpcd.c:764) by 0x57E0F06: ??? (udev.c:97)
    by 0x42EB62: dev_handle_data (dev.c:153)
    by 0x408A74: eloop_start (eloop.c:399)
    by 0x4073B6: main (dhcpcd.c:1537)

So this patch makes handle_interface() interfaces that are already known. This
fixes the segfault, but I'm not sure if it's always the right thing to do (maybe
there are actions that need to be performed even for duplicate additions?).

diff -ru -x '*~' dhcpcd-6.4.0-orig/dhcpcd.c dhcpcd-6.4.0/dhcpcd.c
--- dhcpcd-6.4.0-orig/dhcpcd.c	2014-06-14 22:13:12.000000000 +0200
+++ dhcpcd-6.4.0/dhcpcd.c	2014-07-03 11:13:39.133186533 +0200
@@ -774,11 +774,11 @@
 		} else {
 			TAILQ_REMOVE(ifs, ifp, next);
 			TAILQ_INSERT_TAIL(ctx->ifaces, ifp, next);
-		}
-		if (action > 0) {
-			init_state(ifp, ctx->argc, ctx->argv);
-			run_preinit(ifp);
-			dhcpcd_startinterface(ifp);
+			if (action > 0) {
+				init_state(ifp, ctx->argc, ctx->argv);
+				run_preinit(ifp);
+				dhcpcd_startinterface(ifp);
+			}
 		}
 	}

-- 
Eelco Dolstra | LogicBlox, Inc. | http://nixos.org/~eelco/