Information on bug described in CVS manual (section F1)

[Hendrik Krauß]

Hello,

possibly we have some relevant information for the problem mentioned in 
the CVS manual, section F1 "Partial list of error messages" 
(https://www.cvshome.org/docs/manual/cvs-1.11.14/cvs_21.html#SEC184). 
From that section:

> cvs [server aborted]: received broken pipe signal
>
> This message seems to be caused by a hard-to-track-down bug in CVS or 
> the systems it runs on (we don't know--we haven't tracked it down 
> yet!). [...]


Our setup involves a statically linked CVS 1.11.1p1 running in a chroot 
jail. Today, I added entries to the CVSROOT/loginfo file for automatic 
post-commit processing, and persistently got the error message above. 
Even a very simple command in loginfo, like "echo hello > 
/tmp/somefile", wouldn't work and only produce that error.

The problem went away after copying a (statically linked) sh into the 
chroot jail, so that the CVS executable running in the jail would see it 
as "/bin/sh". My guess is of course that after finding a matching line 
in loginfo, CVS forks and does something like exec("/bin/sh", "-c", 
<line-from-loginfo>), which won't work due to a non-existant /bin/sh. 
Then the parent, unaware that the child died directly, starts writing 
into the child's stdin, which is a widowed pipe, which causes a SIGPIPE 
to the parent, which confuses it and makes it die with the above error.
It was particularly annoying because once I had committed the 
problematic loginfo file, commits would consistently fail with the 
"broken pipe" error message--which also prevented committing a good 
version of loginfo. I had to edit loginfo directly via SSH. By checking 
in a malicious loginfo file, you can effectively make your repository 
read-only (bug? feature?)  :-)

Let me know if this helps tracking down the bug, or part of it. I tried 
to describe everything relevant to the situation, but do contact me if 
you need more details about our setup.

Best regards,
Hendrik Krauss

--
"1 + 1 = 3, for large values of 1."