ksql_open() failure in split-process mode

[cornett]

I recently encountered a situation where ksql_open() failed in
split-process mode, but worked fine otherwise. This is not really a bug
in ksql, but I'm reporting it for the benefit of anyone else who runs
into the same issue.

The problem occurs if you run ksql in split-process mode in a chroot
environment that doesn't include a functioning /dev/null device. It is
worth noting that this is what you get by default on OpenBSD if you just
enable slowcgi and drop a statically linked cgi script into
/var/www/cgi-bin.

If you check the code of sqlite's robust_open() function (src/os_unix.c),
you will see that it wants to return a file descriptor > 2,
and may call open(2) on /dev/null to accomplish this.
If the latter fails, robust_open() returns an error. This behaviour
interacts badly with the code in the child path of ksql_alloc_child(),
which closes stdin and stdout. Without a functioning /dev/null, sqlite
can't fill in those empty descriptor slots and therefore won't open a database.

Once I debugged the problem, fixing it with mknod(8) was
straightforward, but it did require loosening the mount options on
/var, which is not great.

If you wish to work around this in ksql, not closing stdin and stdout in
the child should do it. Otherwise, perhaps a note in the documentation
would help others avoid the problem.

[kristapsdz]

This is a great find---it was also identified by schwarze@ in a code audit. Thank you to both of you! This'll be in the next release.