contrib/init: fix unused variables in openrc script #35978

• Makes it so that ${BITCOIND_BIN} is actually used as command=, rather than the hardcoded /usr/bin/bitcoind.
• Passes BITCOIND_GROUP to start-stop-daemon, so that the daemon process itself runs under it.

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For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35978.

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The variable reuse seems fine, but would you say that passing the group in is a bug fix?

The variable reuse seems fine, but would you say that passing the group in is a bug fix?

Yes, I think it is.

utACK d837bb38a44de445d2c459a477302d78871ae1a6

reply-to: #35978 (comment)

but would you say that passing the group in is a bug fix?

it is a genuine bug fix, just one that rarely triggers because BITCOIND_GROUP defaults to bitcoin, which is also typically the bitcoin user's primary group, so the two coincide by default. it only shows up when BITCOIND_GROUP is overridden to something else

start_pre() already sets the datadir, PID directory, and config file ownership to ${BITCOIND_USER}:${BITCOIND_GROUP}. without -g, the daemon instead runs under the user's primary group, so the two can diverge when BITCOIND_GROUP is intentionally overridden, potentially affecting access to files the daemon creates or accesses at runtime. adding -g ${BITCOIND_GROUP} fixes that by making the daemon use the same group configured by start_pre()

utACK d837bb38a44de445d2c459a477302d78871ae1a6

I also agree this is a bug. Another concrete example I found is -rpccookieperms=group. That makes the .cookie group-readable, but by the user's primary group and not by the BITCOIND_GROUP that start_pre() put on the datadir.