[exim-dev] [Bug 2911] New: setting dns_again_means_nonexist …

https://bugs.exim.org/show_bug.cgi?id=2911

            Bug ID: 2911
           Summary: setting dns_again_means_nonexist to a list containing
                    @mx_ lookups causes segfault
           Product: Exim
           Version: 4.96
          Hardware: x86
                OS: Linux
            Status: NEW
          Severity: bug
          Priority: medium
         Component: List matching
          Assignee: unallocated@???
          Reporter: thomasm-exim@???
                CC: exim-dev@???

Not sure whether this is a bug or a case of "never do such a stupid
configuration"... :-)

I happened to set a domain list using @mx_any and used this list in
dns_again_means_nonexist .

Test case:
domainlist local_domains = @ : @mx_any/ignore=127.0.0.1
dns_again_means_nonexist = !+local_domains

Now if a DNS lookup for a MX gives TRY_AGAIN, exim will check whether the name
MX name is in dns_again_means_nonexist . To do this, it does a MX lookup on the
name, which gives TRY_AGAIN. This leads to an endless loop (debug repeatedly
outputs "DNS lookup of exchange.zenit.de (MX) gave TRY_AGAIN"), until exim
crashes with a Segmentation fault.

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