This commit refactors the use of verify_signed_buffer() outside of gpg-interface.c to use check_signature() instead. It also turns verify_signed_buffer() into a file-local function since it's now only invoked internally by check_signature(). There were previously two globally scoped functions used in different parts of Git to perform GPG signature verification: verify_signed_buffer() and check_signature(). Now only check_signature() is used. The verify_signed_buffer() function doesn't guard against duplicate signatures as described by Michał Górny [1]. Instead it only ensures a non-erroneous exit code from GPG and the presence of at least one GOODSIG status field. This stands in contrast with check_signature() that returns an error if more than one signature is encountered. The lower degree of verification makes the use of verify_signed_buffer() problematic if callers don't parse and validate the various parts of the GPG status message themselves. And processing these messages seems like a task that should be reserved to gpg-interface.c with the function check_signature(). Furthermore, the use of verify_signed_buffer() makes it difficult to introduce new functionality that relies on the content of the GPG status lines. Now all operations that does signature verification share a single entry point to gpg-interface.c. This makes it easier to propagate changed or additional functionality in GPG signature verification to all parts of Git, without having odd edge-cases that don't perform the same degree of verification. [1] https://dev.gentoo.org/~mgorny/articles/attack-on-git-signature-verification.html Signed-off-by: Hans Jerry Illikainen <hji@xxxxxxxxxxxx> --- builtin/fmt-merge-msg.c | 11 +++-- gpg-interface.c | 97 +++++++++++++++++++++-------------------- gpg-interface.h | 9 ---- log-tree.c | 34 +++++++-------- 4 files changed, 73 insertions(+), 78 deletions(-) diff --git a/builtin/fmt-merge-msg.c b/builtin/fmt-merge-msg.c index 736f666f64..172dfbd852 100644 --- a/builtin/fmt-merge-msg.c +++ b/builtin/fmt-merge-msg.c @@ -494,6 +494,7 @@ static void fmt_merge_msg_sigs(struct strbuf *out) enum object_type type; unsigned long size, len; char *buf = read_object_file(oid, &type, &size); + struct signature_check sigc = { 0 }; struct strbuf sig = STRBUF_INIT; if (!buf || type != OBJ_TAG) @@ -502,10 +503,12 @@ static void fmt_merge_msg_sigs(struct strbuf *out) if (size == len) ; /* merely annotated */ - else if (verify_signed_buffer(buf, len, buf + len, size - len, &sig, NULL)) { - if (!sig.len) - strbuf_addstr(&sig, "gpg verification failed.\n"); - } + else if (check_signature(buf, len, buf + len, size - len, &sigc) && + !sigc.gpg_output) + strbuf_addstr(&sig, "gpg verification failed.\n"); + else + strbuf_addstr(&sig, sigc.gpg_output); + signature_check_clear(&sigc); if (!tag_number++) { fmt_tag_signature(&tagbuf, &sig, buf, len); diff --git a/gpg-interface.c b/gpg-interface.c index 165274d74a..2d538bcd6e 100644 --- a/gpg-interface.c +++ b/gpg-interface.c @@ -256,6 +256,55 @@ static void parse_gpg_output(struct signature_check *sigc) FREE_AND_NULL(sigc->key); } +static int verify_signed_buffer(const char *payload, size_t payload_size, + const char *signature, size_t signature_size, + struct strbuf *gpg_output, + struct strbuf *gpg_status) +{ + struct child_process gpg = CHILD_PROCESS_INIT; + struct gpg_format *fmt; + struct tempfile *temp; + int ret; + struct strbuf buf = STRBUF_INIT; + + temp = mks_tempfile_t(".git_vtag_tmpXXXXXX"); + if (!temp) + return error_errno(_("could not create temporary file")); + if (write_in_full(temp->fd, signature, signature_size) < 0 || + close_tempfile_gently(temp) < 0) { + error_errno(_("failed writing detached signature to '%s'"), + temp->filename.buf); + delete_tempfile(&temp); + return -1; + } + + fmt = get_format_by_sig(signature); + if (!fmt) + BUG("bad signature '%s'", signature); + + argv_array_push(&gpg.args, fmt->program); + argv_array_pushv(&gpg.args, fmt->verify_args); + argv_array_pushl(&gpg.args, + "--status-fd=1", + "--verify", temp->filename.buf, "-", + NULL); + + if (!gpg_status) + gpg_status = &buf; + + sigchain_push(SIGPIPE, SIG_IGN); + ret = pipe_command(&gpg, payload, payload_size, + gpg_status, 0, gpg_output, 0); + sigchain_pop(SIGPIPE); + + delete_tempfile(&temp); + + ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG "); + strbuf_release(&buf); /* no matter it was used or not */ + + return ret; +} + int check_signature(const char *payload, size_t plen, const char *signature, size_t slen, struct signature_check *sigc) { @@ -418,51 +467,3 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig return 0; } - -int verify_signed_buffer(const char *payload, size_t payload_size, - const char *signature, size_t signature_size, - struct strbuf *gpg_output, struct strbuf *gpg_status) -{ - struct child_process gpg = CHILD_PROCESS_INIT; - struct gpg_format *fmt; - struct tempfile *temp; - int ret; - struct strbuf buf = STRBUF_INIT; - - temp = mks_tempfile_t(".git_vtag_tmpXXXXXX"); - if (!temp) - return error_errno(_("could not create temporary file")); - if (write_in_full(temp->fd, signature, signature_size) < 0 || - close_tempfile_gently(temp) < 0) { - error_errno(_("failed writing detached signature to '%s'"), - temp->filename.buf); - delete_tempfile(&temp); - return -1; - } - - fmt = get_format_by_sig(signature); - if (!fmt) - BUG("bad signature '%s'", signature); - - argv_array_push(&gpg.args, fmt->program); - argv_array_pushv(&gpg.args, fmt->verify_args); - argv_array_pushl(&gpg.args, - "--status-fd=1", - "--verify", temp->filename.buf, "-", - NULL); - - if (!gpg_status) - gpg_status = &buf; - - sigchain_push(SIGPIPE, SIG_IGN); - ret = pipe_command(&gpg, payload, payload_size, - gpg_status, 0, gpg_output, 0); - sigchain_pop(SIGPIPE); - - delete_tempfile(&temp); - - ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG "); - strbuf_release(&buf); /* no matter it was used or not */ - - return ret; -} diff --git a/gpg-interface.h b/gpg-interface.h index 796571e9e9..f4e9b4f371 100644 --- a/gpg-interface.h +++ b/gpg-interface.h @@ -54,15 +54,6 @@ size_t parse_signature(const char *buf, size_t size); int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key); -/* - * Run "gpg" to see if the payload matches the detached signature. - * gpg_output, when set, receives the diagnostic output from GPG. - * gpg_status, when set, receives the status output from GPG. - */ -int verify_signed_buffer(const char *payload, size_t payload_size, - const char *signature, size_t signature_size, - struct strbuf *gpg_output, struct strbuf *gpg_status); - int git_gpg_config(const char *, const char *, void *); void set_signing_key(const char *); const char *get_signing_key(void); diff --git a/log-tree.c b/log-tree.c index 52127427ff..897a90233e 100644 --- a/log-tree.c +++ b/log-tree.c @@ -449,22 +449,21 @@ static void show_signature(struct rev_info *opt, struct commit *commit) { struct strbuf payload = STRBUF_INIT; struct strbuf signature = STRBUF_INIT; - struct strbuf gpg_output = STRBUF_INIT; + struct signature_check sigc = { 0 }; int status; if (parse_signed_commit(commit, &payload, &signature) <= 0) goto out; - status = verify_signed_buffer(payload.buf, payload.len, - signature.buf, signature.len, - &gpg_output, NULL); - if (status && !gpg_output.len) - strbuf_addstr(&gpg_output, "No signature\n"); - - show_sig_lines(opt, status, gpg_output.buf); + status = check_signature(payload.buf, payload.len, signature.buf, + signature.len, &sigc); + if (status && !sigc.gpg_output) + show_sig_lines(opt, status, "No signature\n"); + else + show_sig_lines(opt, status, sigc.gpg_output); + signature_check_clear(&sigc); out: - strbuf_release(&gpg_output); strbuf_release(&payload); strbuf_release(&signature); } @@ -497,8 +496,9 @@ static int show_one_mergetag(struct commit *commit, struct object_id oid; struct tag *tag; struct strbuf verify_message; + struct signature_check sigc = { 0 }; int status, nth; - size_t payload_size, gpg_message_offset; + size_t payload_size; hash_object_file(the_hash_algo, extra->value, extra->len, type_name(OBJ_TAG), &oid); @@ -520,19 +520,19 @@ static int show_one_mergetag(struct commit *commit, else strbuf_addf(&verify_message, "parent #%d, tagged '%s'\n", nth + 1, tag->tag); - gpg_message_offset = verify_message.len; payload_size = parse_signature(extra->value, extra->len); status = -1; if (extra->len > payload_size) { /* could have a good signature */ - if (!verify_signed_buffer(extra->value, payload_size, - extra->value + payload_size, - extra->len - payload_size, - &verify_message, NULL)) - status = 0; /* good */ - else if (verify_message.len <= gpg_message_offset) + status = check_signature(extra->value, payload_size, + extra->value + payload_size, + extra->len - payload_size, &sigc); + if (sigc.gpg_output) + strbuf_addstr(&verify_message, sigc.gpg_output); + else strbuf_addstr(&verify_message, "No signature\n"); + signature_check_clear(&sigc); /* otherwise we couldn't verify, which is shown as bad */ } -- 2.25.1.709.g558d21736a
