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
  17 /*
  18  * We refuse to tag something we can't verify. Just because.
  19  */
  20 static int verify_object(unsigned char *sha1, const char *expected_type)
  21 {
  22         int ret = -1;
  23         enum object_type type;
  24         unsigned long size;
  25         void *buffer = read_sha1_file(sha1, &type, &size);
  26
  27         if (buffer) {
  28                 if (type == type_from_string(expected_type))
  29                         ret = check_sha1_signature(sha1, buffer, size, expected_type);
  30                 free(buffer);
  31         }
  32         return ret;
  33 }
  34
  35 #ifdef NO_C99_FORMAT
  36 #define PD_FMT "%d"
  37 #else
  38 #define PD_FMT "%td"
  39 #endif
  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 !");
  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 \"", 0);
  57
  58         if (get_sha1_hex(object + 7, sha1))
  59                 return error("char%d: could not get SHA1 hash", 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 \"", 47);
  65
  66         /* Verify tag-line */
  67         tag_line = strchr(type_line, '\n');
  68         if (!tag_line)
  69                 return error("char" PD_FMT ": could not find next \"\\n\"", type_line - buffer);
  70         tag_line++;
  71         if (memcmp(tag_line, "tag ", 4) || tag_line[4] == '\n')
  72                 return error("char" PD_FMT ": no \"tag \" found", 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" PD_FMT ": type too long", 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 (verify_object(sha1, type))
  84                 return error("char%d: could not verify object %s", 7, sha1_to_hex(sha1));
  85
  86         /* Verify the tag-name: we don't allow control characters or spaces in it */
  87         tag_line += 4;
  88         for (;;) {
  89                 unsigned char c = *tag_line++;
  90                 if (c == '\n')
  91                         break;
  92                 if (c > ' ')
  93                         continue;
  94                 return error("char" PD_FMT ": could not verify tag name", tag_line - buffer);
  95         }
  96
  97         /* Verify the tagger line */
  98         tagger_line = tag_line;
  99
 100         if (memcmp(tagger_line, "tagger", 6) || (tagger_line[6] == '\n'))
 101                 return error("char" PD_FMT ": could not find \"tagger\"", tagger_line - buffer);
 102
 103         /* TODO: check for committer info + blank line? */
 104         /* Also, the minimum length is probably + "tagger .", or 63+8=71 */
 105
 106         /* The actual stuff afterwards we don't care about.. */
 107         return 0;
 108 }
 109
 110 #undef PD_FMT
 111
 112 int main(int argc, char **argv)
 113 {
 114         unsigned long size = 4096;
 115         char *buffer = xmalloc(size);
 116         unsigned char result_sha1[20];
 117
 118         if (argc != 1)
 119                 usage("git-mktag < signaturefile");
 120
 121         setup_git_directory();
 122
 123         if (read_fd(0, &buffer, &size)) {
 124                 free(buffer);
 125                 die("could not read from stdin");
 126         }
 127
 128         /* Verify it for some basic sanity: it needs to start with
 129            "object <sha1>\ntype\ntagger " */
 130         if (verify_tag(buffer, size) < 0)
 131                 die("invalid tag signature file");
 132
 133         if (write_sha1_file(buffer, size, tag_type, result_sha1) < 0)
 134                 die("unable to write tag file");
 135
 136         free(buffer);
 137
 138         printf("%s\n", sha1_to_hex(result_sha1));
 139         return 0;
 140 }