mktag.c

   1 #include "cache.h"
   2 #include "tag.h"
   3
   4 /*
   5  * A signature file has a very simple fixed format: four lines
   6  * of "object <sha1>" + "type <typename>" + "tag <tagname>" +
   7  * "tagger <committer>", followed by a blank line, a free-form tag
   8  * message and a signature block that git itself doesn't care about,
   9  * but that can be verified with gpg or similar.
  10  *
  11  * The first three lines are guaranteed to be at least 63 bytes:
  12  * "object <sha1>\n" is 48 bytes, "type tag\n" at 9 bytes is the
  13  * shortest possible type-line, and "tag .\n" at 6 bytes is the
  14  * shortest single-character-tag line.
  15  *
  16  * We also artificially limit the size of the full object to 8kB.
  17  * Just because I'm a lazy bastard, and if you can't fit a signature
  18  * in that size, you're doing something wrong.
  19  */
  20
  21 /* Some random size */
  22 #define MAXSIZE (8192)
  23
  24 /*
  25  * We refuse to tag something we can't verify. Just because.
  26  */
  27 static int verify_object(unsigned char *sha1, const char *expected_type)
  28 {
  29         int ret = -1;
  30         enum object_type type;
  31         unsigned long size;
  32         void *buffer = read_sha1_file(sha1, &type, &size);
  33
  34         if (buffer) {
  35                 if (type == type_from_string(expected_type))
  36                         ret = check_sha1_signature(sha1, buffer, size, expected_type);
  37                 free(buffer);
  38         }
  39         return ret;
  40 }
  41
  42 #ifdef NO_C99_FORMAT
  43 #define PD_FMT "%d"
  44 #else
  45 #define PD_FMT "%td"
  46 #endif
  47
  48 static int verify_tag(char *buffer, unsigned long size)
  49 {
  50         int typelen;
  51         char type[20];
  52         unsigned char sha1[20];
  53         const char *object, *type_line, *tag_line, *tagger_line;
  54
  55         if (size < 64)
  56                 return error("wanna fool me ? you obviously got the size wrong !");
  57
  58         buffer[size] = 0;
  59
  60         /* Verify object line */
  61         object = buffer;
  62         if (memcmp(object, "object ", 7))
  63                 return error("char%d: does not start with \"object \"", 0);
  64
  65         if (get_sha1_hex(object + 7, sha1))
  66                 return error("char%d: could not get SHA1 hash", 7);
  67
  68         /* Verify type line */
  69         type_line = object + 48;
  70         if (memcmp(type_line - 1, "\ntype ", 6))
  71                 return error("char%d: could not find \"\\ntype \"", 47);
  72
  73         /* Verify tag-line */
  74         tag_line = strchr(type_line, '\n');
  75         if (!tag_line)
  76                 return error("char" PD_FMT ": could not find next \"\\n\"", type_line - buffer);
  77         tag_line++;
  78         if (memcmp(tag_line, "tag ", 4) || tag_line[4] == '\n')
  79                 return error("char" PD_FMT ": no \"tag \" found", tag_line - buffer);
  80
  81         /* Get the actual type */
  82         typelen = tag_line - type_line - strlen("type \n");
  83         if (typelen >= sizeof(type))
  84                 return error("char" PD_FMT ": type too long", type_line+5 - buffer);
  85
  86         memcpy(type, type_line+5, typelen);
  87         type[typelen] = 0;
  88
  89         /* Verify that the object matches */
  90         if (verify_object(sha1, type))
  91                 return error("char%d: could not verify object %s", 7, sha1_to_hex(sha1));
  92
  93         /* Verify the tag-name: we don't allow control characters or spaces in it */
  94         tag_line += 4;
  95         for (;;) {
  96                 unsigned char c = *tag_line++;
  97                 if (c == '\n')
  98                         break;
  99                 if (c > ' ')
 100                         continue;
 101                 return error("char" PD_FMT ": could not verify tag name", tag_line - buffer);
 102         }
 103
 104         /* Verify the tagger line */
 105         tagger_line = tag_line;
 106
 107         if (memcmp(tagger_line, "tagger", 6) || (tagger_line[6] == '\n'))
 108                 return error("char" PD_FMT ": could not find \"tagger\"", tagger_line - buffer);
 109
 110         /* TODO: check for committer info + blank line? */
 111         /* Also, the minimum length is probably + "tagger .", or 63+8=71 */
 112
 113         /* The actual stuff afterwards we don't care about.. */
 114         return 0;
 115 }
 116
 117 #undef PD_FMT
 118
 119 int main(int argc, char **argv)
 120 {
 121         unsigned long size = 4096;
 122         char *buffer = xmalloc(size);
 123         unsigned char result_sha1[20];
 124
 125         if (argc != 1)
 126                 usage("git-mktag < signaturefile");
 127
 128         setup_git_directory();
 129
 130         if (read_pipe(0, &buffer, &size)) {
 131                 free(buffer);
 132                 die("could not read from stdin");
 133         }
 134
 135         /* Verify it for some basic sanity: it needs to start with
 136            "object <sha1>\ntype\ntagger " */
 137         if (verify_tag(buffer, size) < 0)
 138                 die("invalid tag signature file");
 139
 140         if (write_sha1_file(buffer, size, tag_type, result_sha1) < 0)
 141                 die("unable to write tag file");
 142
 143         free(buffer);
 144
 145         printf("%s\n", sha1_to_hex(result_sha1));
 146         return 0;
 147 }