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authorHans Jerry Illikainen <hji@dyntopia.com>2019-12-27 13:55:57 (GMT)
committerJunio C Hamano <gitster@pobox.com>2020-01-15 22:06:06 (GMT)
commit54887b46890582e60fcb8ee1f287f62870c2ac0f (patch)
tree50902c6b57716469768851ed1017c4aedbdc8365 /gpg-interface.h
parentc58ae96fc4bb11916b62a96940bb70bb85ea5992 (diff)
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gpg-interface: add minTrustLevel as a configuration option
Previously, signature verification for merge and pull operations checked if the key had a trust-level of either TRUST_NEVER or TRUST_UNDEFINED in verify_merge_signature(). If that was the case, the process die()d. The other code paths that did signature verification relied entirely on the return code from check_commit_signature(). And signatures made with a good key, irregardless of its trust level, was considered valid by check_commit_signature(). This difference in behavior might induce users to erroneously assume that the trust level of a key in their keyring is always considered by Git, even for operations where it is not (e.g. during a verify-commit or verify-tag). The way it worked was by gpg-interface.c storing the result from the key/signature status *and* the lowest-two trust levels in the `result` member of the signature_check structure (the last of these status lines that were encountered got written to `result`). These are documented in GPG under the subsection `General status codes` and `Key related`, respectively [1]. The GPG documentation says the following on the TRUST_ status codes [1]: """ These are several similar status codes: - TRUST_UNDEFINED <error_token> - TRUST_NEVER <error_token> - TRUST_MARGINAL [0 [<validation_model>]] - TRUST_FULLY [0 [<validation_model>]] - TRUST_ULTIMATE [0 [<validation_model>]] For good signatures one of these status lines are emitted to indicate the validity of the key used to create the signature. The error token values are currently only emitted by gpgsm. """ My interpretation is that the trust level is conceptionally different from the validity of the key and/or signature. That seems to also have been the assumption of the old code in check_signature() where a result of 'G' (as in GOODSIG) and 'U' (as in TRUST_NEVER or TRUST_UNDEFINED) were both considered a success. The two cases where a result of 'U' had special meaning were in verify_merge_signature() (where this caused git to die()) and in format_commit_one() (where it affected the output of the %G? format specifier). I think it makes sense to refactor the processing of TRUST_ status lines such that users can configure a minimum trust level that is enforced globally, rather than have individual parts of git (e.g. merge) do it themselves (except for a grace period with backward compatibility). I also think it makes sense to not store the trust level in the same struct member as the key/signature status. While the presence of a TRUST_ status code does imply that the signature is good (see the first paragraph in the included snippet above), as far as I can tell, the order of the status lines from GPG isn't well-defined; thus it would seem plausible that the trust level could be overwritten with the key/signature status if they were stored in the same member of the signature_check structure. This patch introduces a new configuration option: gpg.minTrustLevel. It consolidates trust-level verification to gpg-interface.c and adds a new `trust_level` member to the signature_check structure. Backward-compatibility is maintained by introducing a special case in verify_merge_signature() such that if no user-configurable gpg.minTrustLevel is set, then the old behavior of rejecting TRUST_UNDEFINED and TRUST_NEVER is enforced. If, on the other hand, gpg.minTrustLevel is set, then that value overrides the old behavior. Similarly, the %G? format specifier will continue show 'U' for signatures made with a key that has a trust level of TRUST_UNDEFINED or TRUST_NEVER, even though the 'U' character no longer exist in the `result` member of the signature_check structure. A new format specifier, %GT, is also introduced for users that want to show all possible trust levels for a signature. Another approach would have been to simply drop the trust-level requirement in verify_merge_signature(). This would also have made the behavior consistent with other parts of git that perform signature verification. However, requiring a minimum trust level for signing keys does seem to have a real-world use-case. For example, the build system used by the Qubes OS project currently parses the raw output from verify-tag in order to assert a minimum trust level for keys used to sign git tags [2]. [1] https://git.gnupg.org/cgi-bin/gitweb.cgi?p=gnupg.git;a=blob;f=doc/doc/DETAILS;h=bd00006e933ac56719b1edd2478ecd79273eae72;hb=refs/heads/master [2] https://github.com/QubesOS/qubes-builder/blob/9674c1991deef45b1a1b1c71fddfab14ba50dccf/scripts/verify-git-tag#L43 Signed-off-by: Hans Jerry Illikainen <hji@dyntopia.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'gpg-interface.h')
-rw-r--r--gpg-interface.h10
1 files changed, 9 insertions, 1 deletions
diff --git a/gpg-interface.h b/gpg-interface.h
index 3e624ec..796571e 100644
--- a/gpg-interface.h
+++ b/gpg-interface.h
@@ -7,6 +7,14 @@ struct strbuf;
#define GPG_VERIFY_RAW 2
#define GPG_VERIFY_OMIT_STATUS 4
+enum signature_trust_level {
+ TRUST_UNDEFINED,
+ TRUST_NEVER,
+ TRUST_MARGINAL,
+ TRUST_FULLY,
+ TRUST_ULTIMATE,
+};
+
struct signature_check {
char *payload;
char *gpg_output;
@@ -16,7 +24,6 @@ struct signature_check {
* possible "result":
* 0 (not checked)
* N (checked but no further result)
- * U (untrusted good)
* G (good)
* B (bad)
*/
@@ -25,6 +32,7 @@ struct signature_check {
char *key;
char *fingerprint;
char *primary_key_fingerprint;
+ enum signature_trust_level trust_level;
};
void signature_check_clear(struct signature_check *sigc);