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 || size > MAXSIZE-1)
  49                 return -1;
  50         buffer[size] = 0;
  51
  52         /* Verify object line */
  53         object = buffer;
  54         if (memcmp(object, "object ", 7))
  55                 return -1;
  56         if (get_sha1_hex(object + 7, sha1))
  57                 return -1;
  58
  59         /* Verify type line */
  60         type_line = object + 48;
  61         if (memcmp(type_line - 1, "\ntype ", 6))
  62                 return -1;
  63
  64         /* Verify tag-line */
  65         tag_line = strchr(type_line, '\n');
  66         if (!tag_line)
  67                 return -1;
  68         tag_line++;
  69         if (memcmp(tag_line, "tag ", 4) || tag_line[4] == '\n')
  70                 return -1;
  71
  72         /* Get the actual type */
  73         typelen = tag_line - type_line - strlen("type \n");
  74         if (typelen >= sizeof(type))
  75                 return -1;
  76         memcpy(type, type_line+5, typelen);
  77         type[typelen] = 0;
  78
  79         /* Verify that the object matches */
  80         if (get_sha1_hex(object + 7, sha1))
  81                 return -1;
  82         if (verify_object(sha1, type))
  83                 return -1;
  84
  85         /* Verify the tag-name: we don't allow control characters or spaces in it */
  86         tag_line += 4;
  87         for (;;) {
  88                 unsigned char c = *tag_line++;
  89                 if (c == '\n')
  90                         break;
  91                 if (c > ' ')
  92                         continue;
  93                 return -1;
  94         }
  95
  96         /* Verify the tagger line */
  97         tagger_line = tag_line;
  98
  99         if (memcmp(tagger_line, "tagger", 6) || (tagger_line[6] == '\n'))
 100                 return -1;
 101
 102         /* The actual stuff afterwards we don't care about.. */
 103         return 0;
 104 }
 105
 106 int main(int argc, char **argv)
 107 {
 108         unsigned long size;
 109         char buffer[MAXSIZE];
 110         unsigned char result_sha1[20];
 111
 112         if (argc != 1)
 113                 usage("cat <signaturefile> | git-mktag");
 114
 115         setup_git_directory();
 116
 117         // Read the signature
 118         size = 0;
 119         for (;;) {
 120                 int ret = xread(0, buffer + size, MAXSIZE - size);
 121                 if (ret <= 0)
 122                         break;
 123                 size += ret;
 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         printf("%s\n", sha1_to_hex(result_sha1));
 133         return 0;
 134 }