[FFmpeg-devel] [PATCH] Avoid sending packets to network when multicast ttl is 0 in udp

[Michael Niedermayer]

On Wed, Jul 13, 2016 at 03:09:28PM +0430, Omid Ghaffarinia wrote:
> I attached the patch.
> 
> The actual bug is, when creating a local multicast stream (i.e. giving
> "rtp://224.1.1.1:10000?ttl=0" to avio_open), then you can see the
> packets on the network and not just on local machine (despite setting
> multicast ttl to 0) which was a security bug in my purpose of usage
> (it also made a lot of unused traffic on network)
> 
> The user does not choose to enable/disable the kernel hack, that is
> how it is designed.
> 
> This behavior does NOT happen in Windows machines, but the patch given
> does no harm at all (it does nothing in Windows)
> 
> On Wed, Jul 13, 2016 at 3:12 AM, Moritz Barsnick <barsnick at gmx.net> wrote:
> > On Tue, Jul 12, 2016 at 18:31:36 +0430, Omid Ghaffarinia wrote:
> >
> > Your mailer has broken the patch by inserting line breaks. You should
> > try attaching the patch as a file, or directly using "git send-email".
> >
> >> Bug is due to kernel handling multicast ttl 0 differently (as noted in
> >> kernel code net/ipv4/route.c:2191 see:
> >
> > ffmpeg is not a Linux-only tool/library, so comments should point out
> > which "kernel" more precisely (and possibly which versions this applies
> > to). Admitted, the link to github contains the string "linux". ;-)
> >
> > Furthermore: Please explain what the actual bug (i.e. misbehavior) is,
> > and what this fix changes (or how it fixes it).
> >
> > Are you allowing ffmpeg to work when the user is making use of the
> > kernel hack?
> >
> > What does this patch achieve on non-Linux operating systems?
> >
> > (Sorry for the stupid questions, all this isn't obvious to me, and I do
> > have at least some understanding of network stuff.)
> >
> > Moritz
> > _______________________________________________
> > ffmpeg-devel mailing list
> > ffmpeg-devel at ffmpeg.org
> > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel

>  sdp.c |    2 +-
>  udp.c |   28 ++++++++++++++++++++++++++++
>  2 files changed, 29 insertions(+), 1 deletion(-)
> 697cb044e811d35b10a74ad9ca9181b372affc40  0001-Avoid-sending-packets-to-network-when-multicast-ttl-.patch
> From aab1658d011f5b3eabd22ddc30f40107c6311c92 Mon Sep 17 00:00:00 2001
> From: Omid Ghaffarinia <omid.ghaffarinia at gmail.com>
> Date: Tue, 12 Jul 2016 18:23:57 +0430
> Subject: [PATCH] Avoid sending packets to network when multicast ttl is 0 in
>  udp
> 
> Signed-off-by: Omid Ghaffarinia <omid.ghaffarinia at gmail.com>
> ---
>  libavformat/sdp.c |    2 +-
>  libavformat/udp.c |   28 ++++++++++++++++++++++++++++
>  2 files changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/libavformat/sdp.c b/libavformat/sdp.c
> index 01b564b..0401f7a 100644
> --- a/libavformat/sdp.c
> +++ b/libavformat/sdp.c
> @@ -61,7 +61,7 @@ static void sdp_write_address(char *buff, int size, const char *dest_addr,
>      if (dest_addr) {
>          if (!dest_type)
>              dest_type = "IP4";
> -        if (ttl > 0 && !strcmp(dest_type, "IP4")) {
> +        if (ttl >= 0 && !strcmp(dest_type, "IP4")) {
>              /* The TTL should only be specified for IPv4 multicast addresses,
>               * not for IPv6. */
>              av_strlcatf(buff, size, "c=IN %s %s/%d\r\n", dest_type, dest_addr, ttl);
> diff --git a/libavformat/udp.c b/libavformat/udp.c
> index 8699c1c..fe46ba5 100644
> --- a/libavformat/udp.c
> +++ b/libavformat/udp.c
> @@ -176,6 +176,28 @@ static int udp_set_multicast_ttl(int sockfd, int mcastTTL,
>          }
>      }
>  #endif
> +    if (mcastTTL == 0) {
> +#ifdef IP_MULTICAST_IF
> +        if (addr->sa_family == AF_INET) {
> +            struct in_addr localhost_addr;
> +            inet_pton(AF_INET, "127.0.0.1", &localhost_addr);
> +            if (setsockopt(sockfd, IPPROTO_IP, IP_MULTICAST_IF, &localhost_addr, sizeof(localhost_addr)) < 0) {
> +                log_net_error(NULL, AV_LOG_ERROR, "setsockopt(IP_MULTICAST_IF)");
> +                return -1;
> +            }
> +        }
> +#endif
> +#if defined(IPPROTO_IPV6) && defined(IPV6_MULTICAST_IF)
> +        if (addr->sa_family == AF_INET6) {
> +            struct in6_addr localhost_addr;
> +            inet_pton(AF_INET6, "::1", &localhost_addr);
> +            if (setsockopt(sockfd, IPPROTO_IPV6, IPV6_MULTICAST_IF, &localhost_addr, sizeof(localhost_addr)) < 0) {
> +                log_net_error(NULL, AV_LOG_ERROR, "setsockopt(IPV6_MULTICAST_IF)");
> +                return -1;
> +            }
> +        }
> +#endif

breaks build with mingw64
libavformat/udp.c:183:13: error: implicit declaration of function ‘inet_pton’ [-Werror=implicit-function-declaration]


> +    }
>      return 0;
>  }
>  
> @@ -882,6 +904,12 @@ static int udp_open(URLContext *h, const char *uri, int flags)
>          }
>          if (h->flags & AVIO_FLAG_READ) {
>              /* input */
> +        	if (s->ttl == 0) {
> +            	if (s->dest_addr.ss_family == AF_INET)
> +            		inet_pton(AF_INET, "127.0.0.1", &((struct sockaddr_in *)&s->local_addr_storage)->sin_addr);
> +            	else
> +            		inet_pton(AF_INET6, "::1", &((struct sockaddr_in6 *)&s->local_addr_storage)->sin6_addr);
> +        	}

tabs are not allowed in ffmpeg git

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 181 bytes
Desc: Digital signature
URL: <http://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20160720/4c3294c3/attachment.sig>