git-mktag.c

   1 #include "cache.h"
   2
   3 /*
   4  * A signature file has a very simple fixed format: three lines
   5  * of "object <sha1>" + "type <typename>" + "tag <tagname>",
   6  * followed by some free-form signature that git itself doesn't
   7  * care about, but that can be verified with gpg or similar.
   8  *
   9  * The first three lines are guaranteed to be at least 63 bytes:
  10  * "object <sha1>\n" is 48 bytes, "type tag\n" at 9 bytes is the
  11  * shortest possible type-line, and "tag .\n" at 6 bytes is the
  12  * shortest single-character-tag line.
  13  *
  14  * We also artificially limit the size of the full object to 8kB.
  15  * Just because I'm a lazy bastard, and if you can't fit a signature
  16  * in that size, you're doing something wrong.
  17  */
  18
  19 // Some random size
  20 #define MAXSIZE (8192)
  21
  22 /*
  23  * We refuse to tag something we can't verify. Just because.
  24  */
  25 static int verify_object(unsigned char *sha1, const char *expected_type)
  26 {
  27         int ret = -1;
  28         unsigned long mapsize;
  29         void *map = map_sha1_file(sha1, &mapsize);
  30
  31         if (map) {
  32                 char type[100];
  33                 unsigned long size;
  34                 void *buffer = unpack_sha1_file(map, mapsize, type, &size);
  35
  36                 if (buffer) {
  37                         if (!strcmp(type, expected_type))
  38                                 ret = check_sha1_signature(sha1, buffer, size, type);
  39                         free(buffer);
  40                 }
  41                 munmap(map, mapsize);
  42         }
  43         return ret;
  44 }
  45
  46 static int verify_tag(char *buffer, unsigned long size)
  47 {
  48         int typelen;
  49         char type[20];
  50         unsigned char sha1[20];
  51         const char *object, *type_line, *tag_line;
  52
  53         if (size < 64 || size > MAXSIZE-1)
  54                 return -1;
  55         buffer[size] = 0;
  56
  57         /* Verify object line */
  58         object = buffer;
  59         if (memcmp(object, "object ", 7))
  60                 return -1;
  61         if (get_sha1_hex(object + 7, sha1))
  62                 return -1;
  63
  64         /* Verify type line */
  65         type_line = object + 48;
  66         if (memcmp(type_line - 1, "\ntype ", 6))
  67                 return -1;
  68
  69         /* Verify tag-line */
  70         tag_line = strchr(type_line, '\n');
  71         if (!tag_line)
  72                 return -1;
  73         tag_line++;
  74         if (memcmp(tag_line, "tag ", 4) || tag_line[4] == '\n')
  75                 return -1;
  76
  77         /* Get the actual type */
  78         typelen = tag_line - type_line - strlen("type \n");
  79         if (typelen >= sizeof(type))
  80                 return -1;
  81         memcpy(type, type_line+5, typelen);
  82         type[typelen] = 0;
  83
  84         /* Verify that the object matches */
  85         if (get_sha1_hex(object + 7, sha1))
  86                 return -1;
  87         if (verify_object(sha1, type))
  88                 return -1;
  89
  90         /* Verify the tag-name: we don't allow control characters or spaces in it */
  91         tag_line += 4;
  92         for (;;) {
  93                 unsigned char c = *tag_line++;
  94                 if (c == '\n')
  95                         break;
  96                 if (c > ' ')
  97                         continue;
  98                 return -1;
  99         }
 100
 101         /* The actual stuff afterwards we don't care about.. */
 102         return 0;
 103 }
 104
 105 int main(int argc, char **argv)
 106 {
 107         unsigned long size;
 108         char buffer[MAXSIZE];
 109         unsigned char result_sha1[20];
 110
 111         if (argc != 1)
 112                 usage("cat <signaturefile> | git-mktag");
 113
 114         // Read the signature
 115         size = read(0, buffer, MAXSIZE);
 116
 117         // Verify it for some basic sanity: it needs to start with "object <sha1>\ntag "
 118         if (verify_tag(buffer, size) < 0)
 119                 die("invalid tag signature file");
 120
 121         if (write_sha1_file(buffer, size, "tag", result_sha1) < 0)
 122                 die("unable to write tag file");
 123         printf("%s\n", sha1_to_hex(result_sha1));
 124         return 0;
 125 }