According to gpg2's doc/DETAILS:

    For each signature only one of the codes GOODSIG, BADSIG,
    EXPSIG, EXPKEYSIG, REVKEYSIG or ERRSIG will be emitted.

gpg1 ("classic") behaves the same (although doc/DETAILS differs).

Currently, we parse gpg's status output for GOODSIG, BADSIG and
trust information and translate that into status codes G, B, U, N
for the %G?  format specifier.

git-verify-* returns success in the GOODSIG case only. This is
somewhat in disagreement with gpg, which considers the first 5 of
the 6 above as VALIDSIG, but we err on the very safe side.

Introduce additional status codes E, X, Y, R for ERRSIG, EXPSIG,
EXPKEYSIG, and REVKEYSIG so that a user of %G? gets more information
about the absence of a 'G' on first glance.

Requested-by: Alex <agrambot@gmail.com>
Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Linus's original was rebased to apply to the maintenance track just
in case binary distributors that are stuck in the past want to take
it to their older codebase.  Let's merge it up to more modern
codebase that has Peff's gpg-interface clean-up topic that appeared
after Git 2.9 was tagged.

* lt/gpg-show-long-key-in-signature-verification-maint:
  gpg-interface: prefer "long" key format output when verifying pgp signatures

Yes, gpg2 already uses the long format by default, but most
distributions seem to still have "gpg" be the older 1.x version due to
compatibility reasons.  And older versions of gpg only show the 32-bit
short ID, which is quite insecure.

This doesn't actually matter for the _verification_ itself: if the
verification passes, the pgp signature is good.  But if you don't
actually have the key yet, and want to fetch it, or you want to check
exactly which key was used for verification and want to check it, we
should specify the key with more precision.

In fact, we should preferentially specify the whole key fingerprint, but
gpg doesn't actually support that.  Which is really quite sad.

Showing the "long" format improves things to at least show 64 bits of
the fingerprint.  That's a lot better, even if it's not perfect.

This change the log format for "git log --show-signature" from

    commit 2376d31787760af598db23bb3982a57419854e5c
    merged tag 'v2.9.3'
    gpg: Signature made Fri 12 Aug 2016 09:17:59 AM PDT using RSA key ID 96AFE6CB
    gpg: Good signature from "Junio C Hamano <gitster@pobox.com>"
    gpg:                 aka "Junio C Hamano <jch@google.com>"
    gpg:                 aka "Junio C Hamano <junio@pobox.com>"
    Merge: 2807cd7b25af e0c1ceafc5be
    Author: Junio C Hamano <gitster@pobox.com>
    Date:   Fri Aug 12 10:02:18 2016 -0700

to

    commit 2376d31787760af598db23bb3982a57419854e5c
    merged tag 'v2.9.3'
    gpg: Signature made Fri 12 Aug 2016 09:17:59 AM PDT
    gpg:                using RSA key B0B5E88696AFE6CB
    gpg: Good signature from "Junio C Hamano <gitster@pobox.com>"
    gpg:                 aka "Junio C Hamano <jch@google.com>"
    gpg:                 aka "Junio C Hamano <junio@pobox.com>"
    Merge: 2807cd7b25af e0c1ceafc5be
    Author: Junio C Hamano <gitster@pobox.com>
    Date:   Fri Aug 12 10:02:18 2016 -0700

(note the longer key ID, but also the reflowing of the text) and also
changes the format in the merge messages when merging a signed
tag.

If you already use gpg2 (either because it's installed by default, or
because you have set your gpg_program configuration to point to gpg2),
that already used the long format, you'll also see a change: it will now
have the same formatting as gpg 1.x, and the verification string looks
something like

    gpg: Signature made Sun 24 Jul 2016 12:24:02 PM PDT
    gpg:                using RSA key 79BE3E4300411886
    gpg: Good signature from "Linus Torvalds <torvalds@linux-foundation.org>" [ultimate]

where it used to be on one line:

    gpg: Signature made Sun 24 Jul 2016 12:24:02 PM PDT using RSA key ID 79BE3E4300411886
    gpg: Good signature from "Linus Torvalds <torvalds@linux-foundation.org>" [ultimate]

so there is certainly a chance this could break some automated scripting.
But the 32-bit key ID's really are broken. Also note that because of the
differences between gpg-1.x and gpg-2.x, hopefully any scripted key ID
parsing code (if such code exists) is already flexible enough to not care.

This was triggered by the fact that the "evil32" project keys ended up
leaking to the public key servers, so now there are 32-bit aliases for
just about every open source developer that you can easily get by
mistake if you use the 32-bit short ID format.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

When we create a signature, it may happen that gpg returns with
"success" but not with an actual detached signature on stdout.

Check for the correct signature creation status to catch these cases
better. Really, --status-fd parsing is the only way to check gpg status
reliably. We do the same for verify already.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Similar to the prior commit for verify_signed_buffer, the
motivation here is both to make the code simpler, and to
avoid any possible deadlocks with gpg.

In this case we have the same "write to stdin, then read
from stdout" that the verify case had. This is unlikely to
be a problem in practice, since stdout has the detached
signature, which it cannot compute until it has read all of
stdin (if it were a non-detached signature, that would be a
problem, though).

We don't read from stderr at all currently. However, we will
want to in a future patch, so this also prepares us there
(and in that case gpg _does_ write before reading all of the
input, though again, it is unlikely that a key uid will fill
up a pipe buffer).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

This is shorter and should make the function easier to
follow. But more importantly, it removes the possibility of
any deadlocks based on reading or writing to gpg.

It's not clear if such a deadlock is possible in practice.

We do write the whole payload before reading anything, so we
could deadlock there. However, in practice gpg will need to
read our whole input to verify the signature, so it will
drain our payload first. It could write an error to stderr
before reading, but it's unlikely that such an error
wouldn't be followed by it immediately exiting, or that the
error would actually be larger than a pipe buffer.

On the writing side, we drain stderr (with the
human-readable output) in its entirety before reading stdout
(with the status-fd data). Running strace on "gpg --verify"
does show interleaved output on the two descriptors:

  write(2, "gpg: ", 5)                    = 5
  write(2, "Signature made Thu 16 Jun 2016 0"..., 73) = 73
  write(1, "[GNUPG:] SIG_ID tQw8KGcs9rBfLvAj"..., 66) = 66
  write(1, "[GNUPG:] GOODSIG 69808639F9430ED"..., 60) = 60
  write(2, "gpg: ", 5)                    = 5
  write(2, "Good signature from \"Jeff King <"..., 47) = 47
  write(2, "\n", 1)                       = 1
  write(2, "gpg: ", 5)                    = 5
  write(2, "                aka \"Jeff King <"..., 49) = 49
  write(2, "\n", 1)                       = 1
  write(1, "[GNUPG:] VALIDSIG C49CE24156AF08"..., 135) = 135
  write(1, "[GNUPG:] TRUST_ULTIMATE\n", 24) = 24

The second line written to stdout there contains the
signer's UID, which can be arbitrarily long. If it fills the
pipe buffer, then gpg would block writing to its stdout,
while we are blocked trying to read its stderr.

In practice, GPG seems to limit UIDs to 2048 bytes, so
unless your pipe buffer size is quite small, or unless gpg
does not enforce the limit under some conditions, this seems
unlikely in practice.

Still, it is not hard for us to be cautious and just use
pipe_command.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

We use git_mkstemp to create a temporary file, and try to
clean it up in all exit paths from the function. But that
misses any cases where we die by signal, or by calling die()
in a sub-function. In addition, we missed one of the exit
paths.

Let's convert to using a tempfile object, which handles the
hard cases for us, and add the missing cleanup call. Note
that we would not simply want to rely on program exit to
catch our missed cleanup, as this function may be called
many times in a single program (for the same reason, we use
a static tempfile instead of heap-allocating a new one; that
gives an upper bound on our memory usage).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

If our caller gave us a non-NULL gpg_status parameter, we
write the gpg status into their strbuf. If they didn't, then
we write it to a temporary local strbuf (since we still need
to look at it).  The variable "pbuf" adds an extra layer of
indirection so that the rest of the function can just access
whichever is appropriate.

However, the name "pbuf" isn't very descriptive, and it's
easy to get confused about what is supposed to be in it
(especially because we are reading both "status" and
"output" from gpg).

Rather than give it a more descriptive name, we can just use
gpg_status as our indirection pointer. Either it points to
the caller's input, or we can point it directly to our
temporary buffer.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Our argv allocations are relatively straightforward, but
this avoids us having to manually keep the count up to date
(or create new to-be-replaced slots in the declaration) when
we add new arguments.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

The code for warning_errno/die_errno has been refactored and a new
error_errno() reporting helper is introduced.

* nd/error-errno: (41 commits)
  wrapper.c: use warning_errno()
  vcs-svn: use error_errno()
  upload-pack.c: use error_errno()
  unpack-trees.c: use error_errno()
  transport-helper.c: use error_errno()
  sha1_file.c: use {error,die,warning}_errno()
  server-info.c: use error_errno()
  sequencer.c: use error_errno()
  run-command.c: use error_errno()
  rerere.c: use error_errno() and warning_errno()
  reachable.c: use error_errno()
  mailmap.c: use error_errno()
  ident.c: use warning_errno()
  http.c: use error_errno() and warning_errno()
  grep.c: use error_errno()
  gpg-interface.c: use error_errno()
  fast-import.c: use error_errno()
  entry.c: use error_errno()
  editor.c: use error_errno()
  diff-no-index.c: use error_errno()
  ...