@matheusbsbs / matheus-bagliano / commits / 867386d0c8

tag: sign both hashes

When we write a tag the object oid is specific to the hash algorithm. This matters when a tag is signed. The hash transition plan calls for signatures on both the sha1 form and the sha256 form of the object, and for both of those signatures to live in the tag object. To generate tag object with multiple signatures, first compute the unsigned form of the tag, and then if the tag is being signed compute the unsigned form of the tag with the compatibilityr hash. Then compute compute the signatures of both buffers. Once the signatures are computed add them to both buffers. This allows computing the compatibility hash in do_sign, saving write_object_file the expense of recomputing the compatibility tag just to compute it's hash. Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Eric W. Biederman committed Oct 1, 2023 at 21:40 UTC 867386d0c8aa0ea9edb683585b69b20f96c4f776
1 file changed +41 -4
builtin/tag.c
+41 -4
@@ -28,6 +28,7 @@
28 #include "ref-filter.h"
29 #include "date.h"
30 #include "write-or-die.h"
31 +#include "object-file-convert.h"
32
33 static const char * const git_tag_usage[] = {
34 N_("git tag [-a | -s | -u <key-id>] [-f] [-m <msg> | -F <file>] [-e]\n"
@@ -174,9 +175,43 @@ static int verify_tag(const char *name, const char *ref UNUSED,
175 return 0;
176 }
177
177 -static int do_sign(struct strbuf *buffer)
178 +static int do_sign(struct strbuf *buffer, struct object_id **compat_oid,
179 + struct object_id *compat_oid_buf)
180 {
179 - return sign_buffer(buffer, buffer, get_signing_key());
181 + const struct git_hash_algo *compat = the_repository->compat_hash_algo;
182 + struct strbuf sig = STRBUF_INIT, compat_sig = STRBUF_INIT;
183 + struct strbuf compat_buf = STRBUF_INIT;
184 + const char *keyid = get_signing_key();
185 + int ret = -1;
186 +
187 + if (sign_buffer(buffer, &sig, keyid))
188 + return -1;
189 +
190 + if (compat) {
191 + const struct git_hash_algo *algo = the_repository->hash_algo;
192 +
193 + if (convert_object_file(&compat_buf, algo, compat,
194 + buffer->buf, buffer->len, OBJ_TAG, 1))
195 + goto out;
196 + if (sign_buffer(&compat_buf, &compat_sig, keyid))
197 + goto out;
198 + add_header_signature(&compat_buf, &sig, algo);
199 + strbuf_addbuf(&compat_buf, &compat_sig);
200 + hash_object_file(compat, compat_buf.buf, compat_buf.len,
201 + OBJ_TAG, compat_oid_buf);
202 + *compat_oid = compat_oid_buf;
203 + }
204 +
205 + if (compat_sig.len)
206 + add_header_signature(buffer, &compat_sig, compat);
207 +
208 + strbuf_addbuf(buffer, &sig);
209 + ret = 0;
210 +out:
211 + strbuf_release(&sig);
212 + strbuf_release(&compat_sig);
213 + strbuf_release(&compat_buf);
214 + return ret;
215 }
216
217 static const char tag_template[] =
@@ -249,9 +284,11 @@ static void write_tag_body(int fd, const struct object_id *oid)
284
285 static int build_tag_object(struct strbuf *buf, int sign, struct object_id *result)
286 {
252 - if (sign && do_sign(buf) < 0)
287 + struct object_id *compat_oid = NULL, compat_oid_buf;
288 + if (sign && do_sign(buf, &compat_oid, &compat_oid_buf) < 0)
289 return error(_("unable to sign the tag"));
254 - if (write_object_file(buf->buf, buf->len, OBJ_TAG, result) < 0)
290 + if (write_object_file_flags(buf->buf, buf->len, OBJ_TAG, result,
291 + compat_oid, 0) < 0)
292 return error(_("unable to write tag file"));
293 return 0;
294 }