Re: [Qemu-devel] [PATCH] slirp: tftp, copy sockaddr_size

[Philippe Mathieu-Daudé]

On 03/23/2017 08:31 AM, Marc-André Lureau wrote:
> ASAN detects an "unknown-crash" when running pxe-test:
>
> /ppc64/pxe/spapr-vlan: 
> =================================================================
> ==7143==ERROR: AddressSanitizer: unknown-crash on address 0x7f6dcd298d30 at pc 
> 0x55e22218830d bp 0x7f6dcd2989e0 sp 0x7f6dcd2989d0
> READ of size 128 at 0x7f6dcd298d30 thread T2
>     #0 0x55e22218830c in tftp_session_allocate 
> /home/elmarco/src/qq/slirp/tftp.c:73
>     #1 0x55e22218a1f8 in tftp_handle_rrq /home/elmarco/src/qq/slirp/tftp.c:289
>     #2 0x55e22218b54c in tftp_input /home/elmarco/src/qq/slirp/tftp.c:446
>     #3 0x55e2221833fe in udp6_input /home/elmarco/src/qq/slirp/udp6.c:82

Interesting bug, udp6.c seems to have been started as a copy of udp.c, 
which uses:

        struct sockaddr_storage lhost;
        struct sockaddr_in *lhost4;

but in udp6.c this was changed to:

    struct sockaddr_in6 lhost;

tftp_session_allocate() behavior was fine with IPv4 but dual-stack broke it.

Your fix uses sockaddr_size() which is the cleaner/safer way to do it 
but I'm wondering how to avoid such dual-stack sockaddr issues before 
runtime ASAN spotting.

One way can be to use 'union slirp_sockaddr' recently extracted by Dave 
Gilbert (see http://patchwork.ozlabs.org/patch/746605), it uses more 
stack but this avoid partial underflows.

>     #4 0x55e222137b17 in ip6_input /home/elmarco/src/qq/slirp/ip6_input.c:67
>
> Address 0x7f6dcd298d30 is located in stack of thread T2 at offset 96 in frame
>     #0 0x55e222182420 in udp6_input /home/elmarco/src/qq/slirp/udp6.c:13
>
>   This frame has 3 object(s):
>     [32, 48) '<unknown>'
>     [96, 124) 'lhost' <== Memory access at offset 96 partially overflows this 
> variable
>     [160, 200) 'save_ip' <== Memory access at offset 96 partially underflows 
> this variable
>
> The sockaddr_storage pointer is the sockaddr_in6 lhost on the
> stack. Copy only the source addr size.
>
> Signed-off-by: Marc-André Lureau <address@hidden>

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

> ---
>  slirp/tftp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/slirp/tftp.c b/slirp/tftp.c
> index 50e714807d..a9bc4bb1b6 100644
> --- a/slirp/tftp.c
> +++ b/slirp/tftp.c
> @@ -70,7 +70,7 @@ static int tftp_session_allocate(Slirp *slirp, struct 
> sockaddr_storage *srcsas,
>
>   found:
>    memset(spt, 0, sizeof(*spt));
> -  spt->client_addr = *srcsas;
> +  memcpy(&spt->client_addr, srcsas, sockaddr_size(srcsas));
>    spt->fd = -1;
>    spt->block_size = 512;
>    spt->client_port = tp->udp.uh_sport;