dhcpcd-discuss

Hi Eelco

On 03/07/2014 10:48, Eelco Dolstra wrote:
> 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);
> +			}
>  		}
>  	}


The patch is almost right and the issue has already been fixed in trunk 
a few days ago.
http://roy.marples.name/projects/dhcpcd/ci/bed6e61145ea6f1ac8a7a6926271b4c02f40f0cc?sbs=0
http://roy.marples.name/projects/dhcpcd/ci/49167379dcc1fbe9d39e53fd3f37be3eff43bb5b?sbs=0

Thanks

Roy