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         char type[100];
  29         unsigned long size;
  30         void *buffer = read_sha1_file(sha1, type, &size);
  31
  32         if (buffer) {
  33                 if (!strcmp(type, expected_type))
  34                         ret = check_sha1_signature(sha1, buffer, size, type);
  35                 free(buffer);
  36         }
  37         return ret;
  38 }
  39
  40 static int verify_tag(char *buffer, unsigned long size)
  41 {
  42         int typelen;
  43         char type[20];
  44         unsigned char sha1[20];
  45         const char *object, *type_line, *tag_line;
  46
  47         if (size < 64 || size > MAXSIZE-1)
  48                 return -1;
  49         buffer[size] = 0;
  50
  51         /* Verify object line */
  52         object = buffer;
  53         if (memcmp(object, "object ", 7))
  54                 return -1;
  55         if (get_sha1_hex(object + 7, sha1))
  56                 return -1;
  57
  58         /* Verify type line */
  59         type_line = object + 48;
  60         if (memcmp(type_line - 1, "\ntype ", 6))
  61                 return -1;
  62
  63         /* Verify tag-line */
  64         tag_line = strchr(type_line, '\n');
  65         if (!tag_line)
  66                 return -1;
  67         tag_line++;
  68         if (memcmp(tag_line, "tag ", 4) || tag_line[4] == '\n')
  69                 return -1;
  70
  71         /* Get the actual type */
  72         typelen = tag_line - type_line - strlen("type \n");
  73         if (typelen >= sizeof(type))
  74                 return -1;
  75         memcpy(type, type_line+5, typelen);
  76         type[typelen] = 0;
  77
  78         /* Verify that the object matches */
  79         if (get_sha1_hex(object + 7, sha1))
  80                 return -1;
  81         if (verify_object(sha1, type))
  82                 return -1;
  83
  84         /* Verify the tag-name: we don't allow control characters or spaces in it */
  85         tag_line += 4;
  86         for (;;) {
  87                 unsigned char c = *tag_line++;
  88                 if (c == '\n')
  89                         break;
  90                 if (c > ' ')
  91                         continue;
  92                 return -1;
  93         }
  94
  95         /* The actual stuff afterwards we don't care about.. */
  96         return 0;
  97 }
  98
  99 int main(int argc, char **argv)
 100 {
 101         unsigned long size;
 102         char buffer[MAXSIZE];
 103         unsigned char result_sha1[20];
 104
 105         if (argc != 1)
 106                 usage("cat <signaturefile> | git-mktag");
 107
 108         // Read the signature
 109         size = 0;
 110         for (;;) {
 111                 int ret = read(0, buffer + size, MAXSIZE - size);
 112                 if (!ret)
 113                         break;
 114                 if (ret < 0) {
 115                         if (errno == EAGAIN)
 116                                 continue;
 117                         break;
 118                 }
 119                 size += ret;
 120         }
 121
 122         // Verify it for some basic sanity: it needs to start with "object <sha1>\ntype "
 123         if (verify_tag(buffer, size) < 0)
 124                 die("invalid tag signature file");
 125
 126         if (write_sha1_file(buffer, size, "tag", result_sha1) < 0)
 127                 die("unable to write tag file");
 128         printf("%s\n", sha1_to_hex(result_sha1));
 129         return 0;
 130 }