Michał Górny wrote: > GnuPG supports creating signatures consisting of multiple signature > packets. If such a signature is verified, it outputs all the status > messages for each signature separately. However, git currently does not > account for such scenario and gets terribly confused over getting > multiple *SIG statuses. > > For example, if a malicious party alters a signed commit and appends > a new untrusted signature, git is going to ignore the original bad > signature and report untrusted commit instead. However, %GK and %GS > format strings may still expand to the data corresponding > to the original signature, potentially tricking the scripts into > trusting the malicious commit. > > Given that the use of multiple signatures is quite rare, git does not > support creating them without jumping through a few hoops, and finally > supporting them properly would require extensive API improvement, it > seems reasonable to just reject them at the moment. > ---
Thanks for the clear analysis and fix. May we have your sign-off? See https://www.kernel.org/pub/software/scm/git/docs/SubmittingPatches.html#sign-off (or the equivalent section of your local copy of Documentation/SubmittingPatches) for what this means. > gpg-interface.c | 38 ++++++++++++++++++++++++++++++-------- > 1 file changed, 30 insertions(+), 8 deletions(-) > > diff --git a/gpg-interface.c b/gpg-interface.c > index 09ddfbc26..4e03aec15 100644 > --- a/gpg-interface.c > +++ b/gpg-interface.c > @@ -24,21 +24,23 @@ void signature_check_clear(struct signature_check *sigc) > static struct { > char result; > const char *check; > + int is_status; > } sigcheck_gpg_status[] = { > - { 'G', "\n[GNUPG:] GOODSIG " }, > - { 'B', "\n[GNUPG:] BADSIG " }, > - { 'U', "\n[GNUPG:] TRUST_NEVER" }, > - { 'U', "\n[GNUPG:] TRUST_UNDEFINED" }, > - { 'E', "\n[GNUPG:] ERRSIG "}, > - { 'X', "\n[GNUPG:] EXPSIG "}, > - { 'Y', "\n[GNUPG:] EXPKEYSIG "}, > - { 'R', "\n[GNUPG:] REVKEYSIG "}, > + { 'G', "\n[GNUPG:] GOODSIG ", 1 }, > + { 'B', "\n[GNUPG:] BADSIG ", 1 }, > + { 'U', "\n[GNUPG:] TRUST_NEVER", 0 }, > + { 'U', "\n[GNUPG:] TRUST_UNDEFINED", 0 }, > + { 'E', "\n[GNUPG:] ERRSIG ", 1}, > + { 'X', "\n[GNUPG:] EXPSIG ", 1}, > + { 'Y', "\n[GNUPG:] EXPKEYSIG ", 1}, > + { 'R', "\n[GNUPG:] REVKEYSIG ", 1}, > }; nit: I wonder if making is_status into a flag field (like 'option' in git.c's cmd_struct) and having an explicit SIGNATURE_STATUS value to put there would make this easier to read. It's not clear to me that the name is_status or SIGNATURE_STATUS captures what this field represents. Aren't these all sigcheck statuses? Can you describe briefly what distinguishes the cases where this should be 0 versus 1? > > static void parse_gpg_output(struct signature_check *sigc) > { > const char *buf = sigc->gpg_status; > int i; > + int had_status = 0; > > /* Iterate over all search strings */ > for (i = 0; i < ARRAY_SIZE(sigcheck_gpg_status); i++) { > @@ -50,6 +52,10 @@ static void parse_gpg_output(struct signature_check *sigc) > continue; > found += strlen(sigcheck_gpg_status[i].check); > } > + > + if (sigcheck_gpg_status[i].is_status) > + had_status++; > + > sigc->result = sigcheck_gpg_status[i].result; > /* The trust messages are not followed by key/signer > information */ > if (sigc->result != 'U') { > @@ -62,6 +68,22 @@ static void parse_gpg_output(struct signature_check *sigc) > } > } > } > + > + /* > + * GOODSIG, BADSIG etc. can occur only once for each signature. > + * Therefore, if we had more than one then we're dealing with multiple > + * signatures. We don't support them currently, and they're rather > + * hard to create, so something is likely fishy and we should reject > + * them altogether. > + */ > + if (had_status > 1) { > + sigc->result = 'E'; > + /* Clear partial data to avoid confusion */ > + if (sigc->signer) > + FREE_AND_NULL(sigc->signer); > + if (sigc->key) > + FREE_AND_NULL(sigc->key); > + } Makes sense to me. > } > > int check_signature(const char *payload, size_t plen, const char *signature, > -- > 2.18.0 Can we have a test to make sure this behavior doesn't regress? See t/README for an overview of the test framework and "git grep -e gpg t/" for some examples. The result looks good. Thanks again for writing it. Sincerely, Jonathan
