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#include <assert.h>
#include <ctype.h>
#include <errno.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <sys/stat.h>
#include <openssl/evp.h>
#include <openssl/hmac.h>
void die(const char *format, ...) {
fputs("Fatal: ", stderr);
va_list ap;
va_start(ap, format);
vfprintf(stderr, format, ap);
va_end(ap);
fputc('\n', stderr);
exit(EXIT_FAILURE);
}
#define USAGE "Usage: git-lfs-authenticate <REPO> upload/download"
bool hasprefix(const char *str, const char *prefix) {
if (strlen(prefix) > strlen(str))
return false;
return !strncmp(str, prefix, strlen(prefix));
}
bool hassuffix(const char *str, const char *suffix) {
if (strlen(suffix) > strlen(str))
return false;
str += strlen(str) - strlen(suffix);
return !strcmp(str, suffix);
}
const char *trimspace(const char *str, size_t *length) {
while (*length > 0 && isspace(str[0])) {
str++; (*length)--;
}
while (*length > 0 && isspace(str[*length - 1]))
(*length)--;
return str;
}
void printescjson(const char *str) {
for (size_t i = 0; i < strlen(str); i++) {
switch (str[i]) {
case '"': fputs("\\\"", stdout); break;
case '\\': fputs("\\\\", stdout); break;
case '\b': fputs("\\b", stdout); break;
case '\f': fputs("\\f", stdout); break;
case '\n': fputs("\\n", stdout); break;
case '\r': fputs("\\r", stdout); break;
case '\t': fputs("\\t", stdout); break;
default: fputc(str[i], stdout);
}
}
}
void checkrepopath(const char *path) {
if (strstr(path, "//") || strstr(path, "/./") || strstr(path, "/../")
|| hasprefix(path, "./") || hasprefix(path, "../") || hasprefix(path, "/../"))
die("Bad repository name: Is unresolved path");
if (strlen(path) > 100)
die("Bad repository name: Longer than 100 characters");
if (hasprefix(path, "/"))
die("Bad repository name: Unexpected absolute path");
if (!hassuffix(path, ".git"))
die("Bad repository name: Expected '.git' repo path suffix");
struct stat statbuf;
if (stat(path, &statbuf)) {
if (errno == ENOENT)
die("Repo not found");
die("Could not stat repo: %s", strerror(errno));
}
if (!S_ISDIR(statbuf.st_mode)) {
die("Repo not found");
}
}
char *readkeyfile(const char *path, size_t *len) {
FILE *f = fopen(path, "r");
if (!f)
die("Cannot read key file: %s", strerror(errno));
*len = 0;
size_t bufcap = 4096;
char *buf = malloc(bufcap);
while (!feof(f) && !ferror(f)) {
if (*len + 4096 > bufcap) {
bufcap *= 2;
buf = realloc(buf, bufcap);
}
*len += fread(buf + *len, sizeof(char), 4096, f);
}
if (ferror(f) && !feof(f)) {
OPENSSL_cleanse(buf, *len);
die("Failed to read key file (length: %lu)", *len);
}
fclose(f);
return buf;
}
#define KEYSIZE 64
void readkey(const char *path, uint8_t dest[KEYSIZE]) {
size_t keybuf_len = 0;
char *keybuf = readkeyfile(path, &keybuf_len);
size_t keystr_len = keybuf_len;
const char *keystr = trimspace(keybuf, &keystr_len);
if (keystr_len != 2 * KEYSIZE) {
OPENSSL_cleanse(keybuf, keybuf_len);
die("Bad key length");
}
for (size_t i = 0; i < KEYSIZE; i++) {
const char c = keystr[i];
uint8_t nibble = 0;
if (c >= '0' && c <= '9')
nibble = c - '0';
else if (c >= 'a' && c <= 'f')
nibble = c - 'a' + 10;
else if (c >= 'A' && c <= 'F')
nibble = c - 'A' + 10;
else {
OPENSSL_cleanse(keybuf, keybuf_len);
OPENSSL_cleanse(dest, KEYSIZE);
die("Cannot decode key");
}
size_t ikey = i / 2;
if (i % 2) dest[ikey] |= nibble;
else dest[ikey] = nibble << 4;
}
OPENSSL_cleanse(keybuf, keybuf_len);
free(keybuf);
}
void u64tobe(uint64_t x, uint8_t b[8]) {
b[0] = (uint8_t)(x >> 56);
b[1] = (uint8_t)(x >> 48);
b[2] = (uint8_t)(x >> 40);
b[3] = (uint8_t)(x >> 32);
b[4] = (uint8_t)(x >> 24);
b[5] = (uint8_t)(x >> 16);
b[6] = (uint8_t)(x >> 8);
b[7] = (uint8_t)(x >> 0);
}
void *memcat(void *dest, const void *src, size_t n) {
return memcpy(dest, src, n) + n;
}
#define MAX_TAG_SIZE EVP_MAX_MD_SIZE
typedef struct taginfo {
const char *authtype;
const char *repopath;
const char *operation;
const int64_t expiresat_s;
} taginfo_t;
void maketag(const taginfo_t info, uint8_t key[KEYSIZE], uint8_t dest[MAX_TAG_SIZE], uint32_t *len) {
uint8_t expiresat_b[8];
u64tobe(info.expiresat_s, expiresat_b);
const uint8_t zero[1] = { 0 };
const size_t fullsize = strlen(info.authtype) +
1 + strlen(info.repopath) +
1 + strlen(info.operation) +
1 + sizeof(expiresat_b);
uint8_t *claimbuf = alloca(fullsize);
uint8_t *head = claimbuf;
head = memcat(head, info.authtype, strlen(info.authtype));
head = memcat(head, zero, 1);
head = memcat(head, info.repopath, strlen(info.repopath));
head = memcat(head, zero, 1);
head = memcat(head, info.operation, strlen(info.operation));
head = memcat(head, zero, 1);
head = memcat(head, expiresat_b, sizeof(expiresat_b));
assert(head == claimbuf + fullsize);
memset(dest, 0, MAX_TAG_SIZE);
*len = 0;
if (!HMAC(EVP_sha256(), key, KEYSIZE, claimbuf, fullsize, dest, len)) {
OPENSSL_cleanse(key, KEYSIZE);
die("Failed to generate tag");
}
}
#define MAX_HEXTAG_STRLEN MAX_TAG_SIZE * 2
void makehextag(const taginfo_t info, uint8_t key[KEYSIZE], char dest[MAX_HEXTAG_STRLEN + 1]) {
uint8_t rawtag[MAX_TAG_SIZE];
uint32_t rawtag_len;
maketag(info, key, rawtag, &rawtag_len);
memset(dest, 0, MAX_HEXTAG_STRLEN + 1);
for (size_t i = 0; i < rawtag_len; i++) {
uint8_t b = rawtag[i];
dest[i * 2] = (b >> 4) + ((b >> 4) < 10 ? '0' : 'a');
dest[i*2 + 1] = (b & 0x0F) + ((b & 0x0F) < 10 ? '0' : 'a');
}
}
int main(int argc, char *argv[]) {
if (argc != 3) {
puts(USAGE);
exit(EXIT_FAILURE);
}
const char *repopath = argv[1];
const char *operation = argv[2];
if (strcmp(operation, "download") && strcmp(operation, "upload")) {
puts(USAGE);
exit(EXIT_FAILURE);
}
checkrepopath(repopath);
const char *hrefbase = getenv("GITOLFS3_HREF_BASE");
const char *keypath = getenv("GITOLFS3_KEY_PATH");
if (!hrefbase || strlen(hrefbase) == 0)
die("Incomplete configuration: Base URL not provided");
if (hrefbase[strlen(hrefbase) - 1] != '/')
die("Bad configuration: Base URL should end with slash");
if (!keypath || strlen(keypath) == 0)
die("Incomplete configuration: Key path not provided");
uint8_t key[64];
readkey(keypath, key);
int64_t expiresin_s = 5 * 60;
int64_t expiresat_s = (int64_t)time(NULL) + expiresin_s;
taginfo_t taginfo = {
.authtype = "git-lfs-authenticate",
.repopath = repopath,
.operation = operation,
.expiresat_s = expiresat_s,
};
char hextag[MAX_HEXTAG_STRLEN + 1];
makehextag(taginfo, key, hextag);
printf("{\"header\":{\"Authorization\":\"Gitolfs3-Hmac-Sha256 %s\"},"
"\"expires_in\":%ld,\"href\":\"", hextag, expiresin_s);
printescjson(hrefbase);
printescjson(repopath);
printf("/info/lfs?p=1&te=%ld\"}\n", expiresat_s);
}
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