Re: [FFmpeg-devel] [PATCH 1/2] lavf/udp: set ttl upper bound to 255

["\"zhilizhao(赵志立)\"" <quinkblack@foxmail.com>]

> On Jan 27, 2022, at 12:22 AM, Zhao Zhili <quinkblack@foxmail.com> wrote:
> 
> ---
> libavformat/udp.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavformat/udp.c b/libavformat/udp.c
> index 83c042d079..b441d2ea0d 100644
> --- a/libavformat/udp.c
> +++ b/libavformat/udp.c
> @@ -134,7 +134,7 @@ static const AVOption options[] = {
>     { "reuse",          "explicitly allow reusing UDP sockets",            OFFSET(reuse_socket),   AV_OPT_TYPE_BOOL,   { .i64 = -1 },    -1, 1,       D|E },
>     { "reuse_socket",   "explicitly allow reusing UDP sockets",            OFFSET(reuse_socket),   AV_OPT_TYPE_BOOL,   { .i64 = -1 },    -1, 1,       .flags = D|E },
>     { "broadcast", "explicitly allow or disallow broadcast destination",   OFFSET(is_broadcast),   AV_OPT_TYPE_BOOL,   { .i64 = 0  },     0, 1,       E },
> -    { "ttl",            "Time to live (multicast only)",                   OFFSET(ttl),            AV_OPT_TYPE_INT,    { .i64 = 16 },     0, INT_MAX, E },
> +    { "ttl",            "Time to live (multicast only)",                   OFFSET(ttl),            AV_OPT_TYPE_INT,    { .i64 = 16 },     0, 255,     E },
>     { "connect",        "set if connect() should be called on socket",     OFFSET(is_connected),   AV_OPT_TYPE_BOOL,   { .i64 =  0 },     0, 1,       .flags = D|E },
>     { "fifo_size",      "set the UDP receiving circular buffer size, expressed as a number of packets with size of 188 bytes", OFFSET(circular_buffer_size), AV_OPT_TYPE_INT, {.i64 = 7*4096}, 0, INT_MAX, D },
>     { "overrun_nonfatal", "survive in case of UDP receiving circular buffer overrun", OFFSET(overrun_nonfatal), AV_OPT_TYPE_BOOL, {.i64 = 0}, 0, 1,    D },
> -- 
> 2.29.2
> 

This patchset is related to 'Fix setsockopt IP_MULTICAST_TTL on OpenBSD’.

https://patchwork.ffmpeg.org/project/ffmpeg/patch/Yd5jaXBCd6GP7kBh@humpty.home.comstyle.com/

Looks like it’s impossible to avoid casting int to unsigned char, so integer
overflow/truncation must be handled. Since the maximum value of TTL is 255
limited by IPv4/IPv6, set the upper bound of AVOption to fail early for
invalid value.
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