root/builtin/mktag.c

DEFINITIONS

1. verify_object
2. verify_tag
3. cmd_mktag

#include "builtin.h"
#include "tag.h"

/*
 * A signature file has a very simple fixed format: four lines
 * of "object <sha1>" + "type <typename>" + "tag <tagname>" +
 * "tagger <committer>", followed by a blank line, a free-form tag
 * message and a signature block that git itself doesn't care about,
 * but that can be verified with gpg or similar.
 *
 * The first four lines are guaranteed to be at least 83 bytes:
 * "object <sha1>\n" is 48 bytes, "type tag\n" at 9 bytes is the
 * shortest possible type-line, "tag .\n" at 6 bytes is the shortest
 * single-character-tag line, and "tagger . <> 0 +0000\n" at 20 bytes is
 * the shortest possible tagger-line.
 */

/*
 * We refuse to tag something we can't verify. Just because.
 */
static int verify_object(const unsigned char *sha1, const char *expected_type)
{
        int ret = -1;
        enum object_type type;
        unsigned long size;
        void *buffer = read_sha1_file(sha1, &type, &size);
        const unsigned char *repl = lookup_replace_object(sha1);

        if (buffer) {
                if (type == type_from_string(expected_type))
                        ret = check_sha1_signature(repl, buffer, size, expected_type);
                free(buffer);
        }
        return ret;
}

static int verify_tag(char *buffer, unsigned long size)
{
        int typelen;
        char type[20];
        unsigned char sha1[20];
        const char *object, *type_line, *tag_line, *tagger_line, *lb, *rb;
        size_t len;

        if (size < 84)
                return error("wanna fool me ? you obviously got the size wrong !");

        buffer[size] = 0;

        /* Verify object line */
        object = buffer;
        if (memcmp(object, "object ", 7))
                return error("char%d: does not start with \"object \"", 0);

        if (get_sha1_hex(object + 7, sha1))
                return error("char%d: could not get SHA1 hash", 7);

        /* Verify type line */
        type_line = object + 48;
        if (memcmp(type_line - 1, "\ntype ", 6))
                return error("char%d: could not find \"\\ntype \"", 47);

        /* Verify tag-line */
        tag_line = strchr(type_line, '\n');
        if (!tag_line)
                return error("char%"PRIuMAX": could not find next \"\\n\"",
                                (uintmax_t) (type_line - buffer));
        tag_line++;
        if (memcmp(tag_line, "tag ", 4) || tag_line[4] == '\n')
                return error("char%"PRIuMAX": no \"tag \" found",
                                (uintmax_t) (tag_line - buffer));

        /* Get the actual type */
        typelen = tag_line - type_line - strlen("type \n");
        if (typelen >= sizeof(type))
                return error("char%"PRIuMAX": type too long",
                                (uintmax_t) (type_line+5 - buffer));

        memcpy(type, type_line+5, typelen);
        type[typelen] = 0;

        /* Verify that the object matches */
        if (verify_object(sha1, type))
                return error("char%d: could not verify object %s", 7, sha1_to_hex(sha1));

        /* Verify the tag-name: we don't allow control characters or spaces in it */
        tag_line += 4;
        for (;;) {
                unsigned char c = *tag_line++;
                if (c == '\n')
                        break;
                if (c > ' ')
                        continue;
                return error("char%"PRIuMAX": could not verify tag name",
                                (uintmax_t) (tag_line - buffer));
        }

        /* Verify the tagger line */
        tagger_line = tag_line;

        if (memcmp(tagger_line, "tagger ", 7))
                return error("char%"PRIuMAX": could not find \"tagger \"",
                        (uintmax_t) (tagger_line - buffer));

        /*
         * Check for correct form for name and email
         * i.e. " <" followed by "> " on _this_ line
         * No angle brackets within the name or email address fields.
         * No spaces within the email address field.
         */
        tagger_line += 7;
        if (!(lb = strstr(tagger_line, " <")) || !(rb = strstr(lb+2, "> ")) ||
                strpbrk(tagger_line, "<>\n") != lb+1 ||
                strpbrk(lb+2, "><\n ") != rb)
                return error("char%"PRIuMAX": malformed tagger field",
                        (uintmax_t) (tagger_line - buffer));

        /* Check for author name, at least one character, space is acceptable */
        if (lb == tagger_line)
                return error("char%"PRIuMAX": missing tagger name",
                        (uintmax_t) (tagger_line - buffer));

        /* timestamp, 1 or more digits followed by space */
        tagger_line = rb + 2;
        if (!(len = strspn(tagger_line, "0123456789")))
                return error("char%"PRIuMAX": missing tag timestamp",
                        (uintmax_t) (tagger_line - buffer));
        tagger_line += len;
        if (*tagger_line != ' ')
                return error("char%"PRIuMAX": malformed tag timestamp",
                        (uintmax_t) (tagger_line - buffer));
        tagger_line++;

        /* timezone, 5 digits [+-]hhmm, max. 1400 */
        if (!((tagger_line[0] == '+' || tagger_line[0] == '-') &&
              strspn(tagger_line+1, "0123456789") == 4 &&
              tagger_line[5] == '\n' && atoi(tagger_line+1) <= 1400))
                return error("char%"PRIuMAX": malformed tag timezone",
                        (uintmax_t) (tagger_line - buffer));
        tagger_line += 6;

        /* Verify the blank line separating the header from the body */
        if (*tagger_line != '\n')
                return error("char%"PRIuMAX": trailing garbage in tag header",
                        (uintmax_t) (tagger_line - buffer));

        /* The actual stuff afterwards we don't care about.. */
        return 0;
}

int cmd_mktag(int argc, const char **argv, const char *prefix)
{
        struct strbuf buf = STRBUF_INIT;
        unsigned char result_sha1[20];

        if (argc != 1)
                usage("git mktag");

        if (strbuf_read(&buf, 0, 4096) < 0) {
                die_errno("could not read from stdin");
        }

        /* Verify it for some basic sanity: it needs to start with
           "object <sha1>\ntype\ntagger " */
        if (verify_tag(buf.buf, buf.len) < 0)
                die("invalid tag signature file");

        if (write_sha1_file(buf.buf, buf.len, tag_type, result_sha1) < 0)
                die("unable to write tag file");

        strbuf_release(&buf);
        printf("%s\n", sha1_to_hex(result_sha1));
        return 0;
}