fast-import: add 'strip-if-invalid' mode to '--signed-tags=<mode>'

With c20f112e51 (fast-import: add 'strip-if-invalid' mode to
--signed-commits=<mode>, 2025-11-17), git-fast-import(1) learned to
verify commit signatures during import and strip signatures that fail
verification. Extend the same behavior to signed tag objects by
introducing a 'strip-if-invalid' mode for the '--signed-tags' option.

Signed-off-by: Justin Tobler <jltobler@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/git-fast-import.adoc b/Documentation/git-fast-import.adoc
index 288f2b2a7ead7b56bd4ec5d1613edfad02496e49..d68bc52b7e9cd714b5167573d1881f444020eba4 100644 (file)
--- a/Documentation/git-fast-import.adoc
+++ b/Documentation/git-fast-import.adoc
@@ -66,11 +66,10 @@ fast-import stream! This option is enabled automatically for
 remote-helpers that use the `import` capability, as they are
 already trusted to run their own code.
 
-`--signed-tags=(verbatim|warn-verbatim|warn-strip|strip|abort)`::
+`--signed-tags=<mode>`::
        Specify how to handle signed tags. Behaves in the same way as
-       the `--signed-commits=<mode>` below, except that the
-       `strip-if-invalid` mode is not yet supported. Like for signed
-       commits, the default mode is `verbatim`.
+       the `--signed-commits=<mode>` below. Like for signed commits,
+       the default mode is `verbatim`.
 
 `--signed-commits=<mode>`::
        Specify how to handle signed commits. The following <mode>s

diff --git a/builtin/fast-import.c b/builtin/fast-import.c
index 08ea27242d035c6d737529f6002e32c0b4b58f69..5e89829aea0fe9ca26b856f50b434191cd9123d7 100644 (file)
--- a/builtin/fast-import.c
+++ b/builtin/fast-import.c
@@ -3089,7 +3089,34 @@ static void parse_new_commit(const char *arg)
        b->last_commit = object_count_by_type[OBJ_COMMIT];
 }
 
-static void handle_tag_signature(struct strbuf *msg, const char *name)
+static void handle_tag_signature_if_invalid(struct strbuf *buf,
+                                           struct strbuf *msg,
+                                           size_t sig_offset)
+{
+       struct strbuf signature = STRBUF_INIT;
+       struct strbuf payload = STRBUF_INIT;
+       struct signature_check sigc = { 0 };
+
+       strbuf_addbuf(&payload, buf);
+       strbuf_addch(&payload, '\n');
+       strbuf_add(&payload, msg->buf, sig_offset);
+       strbuf_add(&signature, msg->buf + sig_offset, msg->len - sig_offset);
+
+       sigc.payload_type = SIGNATURE_PAYLOAD_TAG;
+       sigc.payload = strbuf_detach(&payload, &sigc.payload_len);
+
+       if (!check_signature(&sigc, signature.buf, signature.len))
+               goto out;
+
+       strbuf_setlen(msg, sig_offset);
+
+out:
+       signature_check_clear(&sigc);
+       strbuf_release(&signature);
+       strbuf_release(&payload);
+}
+
+static void handle_tag_signature(struct strbuf *buf, struct strbuf *msg, const char *name)
 {
        size_t sig_offset = parse_signed_buffer(msg->buf, msg->len);
 
@@ -3115,6 +3142,9 @@ static void handle_tag_signature(struct strbuf *msg, const char *name)
                /* Truncate the buffer to remove the signature */
                strbuf_setlen(msg, sig_offset);
                break;
+       case SIGN_STRIP_IF_INVALID:
+               handle_tag_signature_if_invalid(buf, msg, sig_offset);
+               break;
 
        /* Third, aborting modes */
        case SIGN_ABORT:
@@ -3123,9 +3153,6 @@ static void handle_tag_signature(struct strbuf *msg, const char *name)
        case SIGN_ABORT_IF_INVALID:
                die(_("'abort-if-invalid' is not a valid mode for "
                      "git fast-import with --signed-tags=<mode>"));
-       case SIGN_STRIP_IF_INVALID:
-               die(_("'strip-if-invalid' is not a valid mode for "
-                     "git fast-import with --signed-tags=<mode>"));
        case SIGN_SIGN_IF_INVALID:
                die(_("'sign-if-invalid' is not a valid mode for "
                      "git fast-import with --signed-tags=<mode>"));
@@ -3198,8 +3225,6 @@ static void parse_new_tag(const char *arg)
        /* tag payload/message */
        parse_data(&msg, 0, NULL);
 
-       handle_tag_signature(&msg, t->name);
-
        /* build the tag object */
        strbuf_reset(&new_data);
 
@@ -3211,6 +3236,9 @@ static void parse_new_tag(const char *arg)
        if (tagger)
                strbuf_addf(&new_data,
                            "tagger %s\n", tagger);
+
+       handle_tag_signature(&new_data, &msg, t->name);
+
        strbuf_addch(&new_data, '\n');
        strbuf_addbuf(&new_data, &msg);
        free(tagger);

diff --git a/t/t9306-fast-import-signed-tags.sh b/t/t9306-fast-import-signed-tags.sh
index 363619e7d1abf13574d825a61462bc1017bfc8f1..fd43b0b52a29a2c6b1f04b0cf0f9ccc5ddf677e9 100755 (executable)
--- a/t/t9306-fast-import-signed-tags.sh
+++ b/t/t9306-fast-import-signed-tags.sh
@@ -77,4 +77,77 @@ test_expect_success GPGSSH 'import SSH signed tag with --signed-tags=strip' '
        test_grep ! "SSH SIGNATURE" out
 '
 
+for mode in strip-if-invalid
+do
+       test_expect_success GPG "import tag with no signature with --signed-tags=$mode" '
+               test_when_finished rm -rf import &&
+               git init import &&
+
+               git fast-export --signed-tags=verbatim >output &&
+               git -C import fast-import --quiet --signed-tags=$mode <output >log 2>&1 &&
+               test_must_be_empty log
+       '
+
+       test_expect_success GPG "keep valid OpenPGP signature with --signed-tags=$mode" '
+               test_when_finished rm -rf import &&
+               git init import &&
+
+               git fast-export --signed-tags=verbatim openpgp-signed >output &&
+               git -C import fast-import --quiet --signed-tags=$mode <output >log 2>&1 &&
+               IMPORTED=$(git -C import rev-parse --verify refs/tags/openpgp-signed) &&
+               test $OPENPGP_SIGNED = $IMPORTED &&
+               git -C import cat-file tag "$IMPORTED" >actual &&
+               test_grep -E "^-----BEGIN PGP SIGNATURE-----" actual &&
+               test_must_be_empty log
+       '
+
+       test_expect_success GPG "handle signature invalidated by message change with --signed-tags=$mode" '
+               test_when_finished rm -rf import &&
+               git init import &&
+
+               git fast-export --signed-tags=verbatim openpgp-signed >output &&
+
+               # Change the tag message, which invalidates the signature. The tag
+               # message length should not change though, otherwise the corresponding
+               # `data <length>` command would have to be changed too.
+               sed "s/OpenPGP signed tag/OpenPGP forged tag/" output >modified &&
+
+               git -C import fast-import --quiet --signed-tags=$mode <modified >log 2>&1 &&
+
+               IMPORTED=$(git -C import rev-parse --verify refs/tags/openpgp-signed) &&
+               test $OPENPGP_SIGNED != $IMPORTED &&
+               git -C import cat-file tag "$IMPORTED" >actual &&
+               test_grep ! -E "^-----BEGIN PGP SIGNATURE-----" actual &&
+               test_must_be_empty log
+       '
+
+       test_expect_success GPGSM "keep valid X.509 signature with --signed-tags=$mode" '
+               test_when_finished rm -rf import &&
+               git init import &&
+
+               git fast-export --signed-tags=verbatim x509-signed >output &&
+               git -C import fast-import --quiet --signed-tags=$mode <output >log 2>&1 &&
+               IMPORTED=$(git -C import rev-parse --verify refs/tags/x509-signed) &&
+               test $X509_SIGNED = $IMPORTED &&
+               git -C import cat-file tag x509-signed >actual &&
+               test_grep -E "^-----BEGIN SIGNED MESSAGE-----" actual &&
+               test_must_be_empty log
+       '
+
+       test_expect_success GPGSSH "keep valid SSH signature with --signed-tags=$mode" '
+               test_when_finished rm -rf import &&
+               git init import &&
+
+               test_config -C import gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+
+               git fast-export --signed-tags=verbatim ssh-signed >output &&
+               git -C import fast-import --quiet --signed-tags=$mode <output >log 2>&1 &&
+               IMPORTED=$(git -C import rev-parse --verify refs/tags/ssh-signed) &&
+               test $SSH_SIGNED = $IMPORTED &&
+               git -C import cat-file tag ssh-signed >actual &&
+               test_grep -E "^-----BEGIN SSH SIGNATURE-----" actual &&
+               test_must_be_empty log
+       '
+done
+
 test_done