mktag.c

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