[pkg-fetchmail-maint] Bug#671294: combination of --plugin and -f - fails

[Alexander Zangerl]

Package: fetchmail
Version: 6.3.18-2
Severity: normal
Tags: patch

this problem applies to both the version in squeeze and sid's 6.3.21-3.

scenario: you want to remote-control fetchmail, but you don't want to write passwords into files,
so you feed fetchmail a minimal rcfile via stdin with -f -. this by itself works fine. if you also 
want or need to use a --plugin (eg. socat for socks), then things fail badly: the plugin is run without
a stdin fd, hence can't take input from fetchmail, lots of fun ensues.
plugins without -f - work fine, it's just the combination that fails.

explanation: the root cause is rcfile_y.y, line 493, which closes whatever fd carried the rcfile. with -f -
this closes fetchmail's stdin - and so far that's unproblematic. 
however, in socket.c lines 166ff things go wrong: fetchmail sets up the plugin with a socketpair, which 
will likely include the first unused fd - and fd zero is now indeed unused. 
in line 180ff a dup2 replumbing from "that fd" (=zero) to zero is performed - and then "that fd" is closed.
and hey presto, we've got no fd zero = stdin for the plugin.

solution: the simplest solution (patch attached) is to make the fclose of the rcfile conditional,
ie. don't close if it's stdin. in the long run the dup2+close code might be made more robust by 
not doing a dup2+close if fd[0] is already 0 or 1.

regards
az
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