[RFC] git-format-patch: default to --from to avoid spoofed mails?

[Josh Triplett <josh@joshtriplett.org>]

When git-format-patch formats a patch authored by someone other than
yourself, it defaults to filling in the "From:" field of the email from
the commit author.  If you explicitly pass the --from option,
git-format-patch will instead use your own committer identity as the
"From:", and then put a "From:" line at the top of the body if the
commit author differs.  (git-am know to use that as the commit author
when applying.)

While git-send-email knows how to change the patch mails to use your own
address as "From:" and add a "From:" line to the body for the author,
any other tool used to send emails doesn't do that.  I've seen more than
a few mails sent to various mailing lists and patch review tools with a
spoofed "From:" field pointing to the commit author, typically without
the knowledge of the author, which can lead to interesting surprises.

I'd like to propose changing the default behavior of git-format-patch to
--from (and adding a --from-author option to override, and perhaps a
config setting).  This will not change the output *except* when
formatting patches authored by someone else.  git-am and git-send-email
both handle the --from format without any issues.

Before I write such a patch: does anyone see a problem with such a
change?

- Josh Triplett