RFR: JDK-8257235: [PATCH] InetAddress.isReachable: Try to use an IPPROTO_ICMP socket type before attempting RAW_SOCK [v2]

[Chris Hegarty]

On Wed, 23 Dec 2020 14:06:12 GMT, Jamie Le Tual <github.com+55101029+jamieletual at openjdk.org> wrote:

>> Users have been able to send ICMP packets without the need for root privileges or the CAP_NET_RAW capability since at least kernel 3.11.
>> 
>> For some time now, if the kernel parameter net.ipv4.ping_group_range included the gid of a user sending an icmp packet with the IPPROTO_ICMP protocol, then the packet would>
>> It's important to note that the both the checksum and ident field are overwritten by the kernel when this is done.
>> 
>> Newer distributions are now setting the default value of net.ipv4.ping_group_range to be open to all possible group ids (Fedora 31 and Ubuntu 20.04 for example) so it can b>
>> 
>> Also of note is the that this is also implemented in MacOS.
>> 
>> This patch proposes attempting to use IPPROTO_ICMP first, and then fall back to attempting a raw socket and ultimately failing over to tcp echo.
>> This patch also alters the logic for identifying icmp reply packets, since the kernel overwrites id ident field when using the IPPROTO_ICMP protocol.
>> The method is similar to that used by the ping(8) utility in the iputils package, where we compare data in the icmp_data member of the icmp struct
>> to identify the packet as our response. The ping utility compares the timeval, whereas this patch proposes to compare both the timeval and the user's pid.
>
> Jamie Le Tual has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fixed formatting

I think that the changes are mostly good. I would like to try them out on my local system and our internal buildAndTest system.

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PR: https://git.openjdk.java.net/jdk/pull/1502