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         char type[100];
  31         unsigned long size;
  32         void *buffer = read_sha1_file(sha1, type, &size);
  33
  34         if (buffer) {
  35                 if (!strcmp(type, expected_type))
  36                         ret = check_sha1_signature(sha1, buffer, size, type);
  37                 free(buffer);
  38         }
  39         return ret;
  40 }
  41
  42 static int verify_tag(char *buffer, unsigned long size)
  43 {
  44         int typelen;
  45         char type[20];
  46         unsigned char sha1[20];
  47         const char *object, *type_line, *tag_line, *tagger_line;
  48
  49         if (size < 64)
  50                 return error("wanna fool me ? you obviously got the size wrong !");
  51
  52         buffer[size] = 0;
  53
  54         /* Verify object line */
  55         object = buffer;
  56         if (memcmp(object, "object ", 7))
  57                 return error("char%d: does not start with \"object \"", 0);
  58
  59         if (get_sha1_hex(object + 7, sha1))
  60                 return error("char%d: could not get SHA1 hash", 7);
  61
  62         /* Verify type line */
  63         type_line = object + 48;
  64         if (memcmp(type_line - 1, "\ntype ", 6))
  65                 return error("char%d: could not find \"\\ntype \"", 47);
  66
  67         /* Verify tag-line */
  68         tag_line = strchr(type_line, '\n');
  69         if (!tag_line)
  70                 return error("char%td: could not find next \"\\n\"", type_line - buffer);
  71         tag_line++;
  72         if (memcmp(tag_line, "tag ", 4) || tag_line[4] == '\n')
  73                 return error("char%td: no \"tag \" found", tag_line - buffer);
  74
  75         /* Get the actual type */
  76         typelen = tag_line - type_line - strlen("type \n");
  77         if (typelen >= sizeof(type))
  78                 return error("char%td: type too long", type_line+5 - buffer);
  79
  80         memcpy(type, type_line+5, typelen);
  81         type[typelen] = 0;
  82
  83         /* Verify that the object matches */
  84         if (verify_object(sha1, type))
  85                 return error("char%d: could not verify object %s", 7, sha1_to_hex(sha1));
  86
  87         /* Verify the tag-name: we don't allow control characters or spaces in it */
  88         tag_line += 4;
  89         for (;;) {
  90                 unsigned char c = *tag_line++;
  91                 if (c == '\n')
  92                         break;
  93                 if (c > ' ')
  94                         continue;
  95                 return error("char%td: could not verify tag name", tag_line - buffer);
  96         }
  97
  98         /* Verify the tagger line */
  99         tagger_line = tag_line;
 100
 101         if (memcmp(tagger_line, "tagger", 6) || (tagger_line[6] == '\n'))
 102                 return error("char%td: could not find \"tagger\"", tagger_line - buffer);
 103
 104         /* TODO: check for committer info + blank line? */
 105         /* Also, the minimum length is probably + "tagger .", or 63+8=71 */
 106
 107         /* The actual stuff afterwards we don't care about.. */
 108         return 0;
 109 }
 110
 111 int main(int argc, char **argv)
 112 {
 113         unsigned long size = 4096;
 114         char *buffer = malloc(size);
 115         unsigned char result_sha1[20];
 116
 117         if (argc != 1)
 118                 usage("cat <signaturefile> | git-mktag");
 119
 120         setup_git_directory();
 121
 122         if (read_pipe(0, &buffer, &size)) {
 123                 free(buffer);
 124                 die("could not read from stdin");
 125         }
 126
 127         /* Verify it for some basic sanity: it needs to start with
 128            "object <sha1>\ntype\ntagger " */
 129         if (verify_tag(buffer, size) < 0)
 130                 die("invalid tag signature file");
 131
 132         if (write_sha1_file(buffer, size, tag_type, result_sha1) < 0)
 133                 die("unable to write tag file");
 134
 135         free(buffer);
 136
 137         printf("%s\n", sha1_to_hex(result_sha1));
 138         return 0;
 139 }