[pkg-fetchmail-maint] Bug#383870: fetchmail: Fetchmail duplicates my SPAM every 10 minutes - ARGH!

[Matthias Andree]

(demoting to serious, tagging upstream, retitling)

Additional info:

fetchmail 6.3.4 and older do NOT log out of the upstream server after
SIGPIPE (I don't know the rationale behind this - it's not in the
comments), which prevents the deletions from happening properly.
Retitling the bug accordingly.

Workarounds:

- have your upstream reject spam with improperly formatted envelopes,
  these should be rejected in the first SMTP dialogue

- do not use multidrop with wildcard ("*"), but list allowed local
  accounts explicitly (since the bogus address will not match, the
  message will be forwarded to the postmaster address, which is under
  your control, and can also be empty to discard the message - this will
  prevent Exim from hanging up).

- set expunge 10  (fetchmail will send QUIT after 10 messages and
                   reconnect, to make deletions effective and limit
                   the amount of refetching).

Fix: block SIGPIPE; the SIGPIPE handler was wrong from the moment it was
coded as it uses longjmp() which isn't safe in signal handlers.
Functions that write to broken pipes will still report errors, but
fetchmail won't corrupt internal state or defeat the logout.

Patch attached. BEWARE: it is NOT run-time tested,
I'm not fetching from multidrop accounts.

Nico/Héctor, can we provide an inofficial package to Helge with the
patch below to ask feedback if the fix is complete? It shouldn't matter
if it's i386 rather than x86_64.

Rationale for severity demotion: Since the breakage is partially induced
by configuration and for instance works properly for singledrop, I don't
think "grave" is justified. Perhaps further demotion to "important" is
in order, but I'm not the Debian maintainer to remove the "unsuitable
for release" tag that is attached to critical/grave/serious severities.

-- 
Matthias Andree
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