Man 3 munge

Name

munge_encode, munge_decode, munge_strerror -- MUNGE core functions

Synopsis

  #include <munge.h>

  munge_err_t munge_encode (char **cred, munge_ctx_t ctx,
                            const void *buf, int len);

  munge_err_t munge_decode (const char *cred, munge_ctx_t ctx,
                            void **buf, int *len, uid_t *uid, gid_t *gid);

  const char * munge_strerror (munge_err_t e);

  cc `pkg-config --cflags --libs munge` -o foo foo.c

Description

The munge_encode() function creates a credential contained in a null-terminated base64 string. A payload specified by a buffer buf of length len can be encapsulated in as well. If the MUNGE context ctx is NULL, the default context will be used. A pointer to the resulting credential is returned via cred; on error, it is set to NULL. The caller is responsible for freeing the memory referenced by cred.

The munge_decode() function validates the null-terminated credential cred. If the MUNGE context ctx is not NULL, it will be set to that used to encode the credential. If buf and len are not NULL, memory will be allocated for the encapsulated payload (up to 1 MB), buf will be set to point to this data, and len will be set to its length. An additional null byte will be appended to this payload data but not included in its length. If no payload exists, buf will be set to NULL and len will be set to 0. For certain errors (i.e., EMUNGE_CRED_EXPIRED, EMUNGE_CRED_REWOUND, EMUNGE_CRED_REPLAYED), payload memory will still be allocated if necessary. The caller is responsible for freeing the memory referenced by buf. If uid or gid is not NULL, they will be set to the UID/GID of the process that created the credential.

The munge_strerror() function returns a descriptive text string describing the MUNGE error number e.

Return Value

The munge_encode() and munge_decode() functions return EMUNGE_SUCCESS on success, or a MUNGE error number otherwise. If a MUNGE context was used, it may contain a more detailed error message accessible via munge_ctx_strerror().

The munge_strerror() function returns a pointer to a null-terminated constant text string; this string should not be freed or modified by the caller.

Errors

• EMUNGE_SUCCESS
  Success.

• EMUNGE_SNAFU
  Internal error.

• EMUNGE_BAD_ARG
  Invalid argument.

• EMUNGE_BAD_LENGTH
  Exceeded the maximum message length as specified by the munged configuration.

• EMUNGE_OVERFLOW
  Exceeded the maximum length of a buffer.

• EMUNGE_NO_MEMORY
  Unable to allocate the requisite memory.

• EMUNGE_SOCKET
  Unable to communicate with the daemon on the domain socket.

• EMUNGE_BAD_CRED
  The credential does not match the specified format.

• EMUNGE_BAD_VERSION
  The credential contains an unsupported version number.

• EMUNGE_BAD_CIPHER
  The credential contains an unsupported cipher type.

• EMUNGE_BAD_MAC
  The credential contains an unsupported MAC type.

• EMUNGE_BAD_ZIP
  The credential contains an unsupported compression type.

• EMUNGE_BAD_REALM
  The credential contains an unrecognized security realm.

• EMUNGE_CRED_INVALID
  The credential is invalid. This means the credential could not be successfully decoded. More than likely, the secret keys on the encoding and decoding hosts do not match. Another possibility is that the credential has been altered since it was encoded.

• EMUNGE_CRED_EXPIRED
  The credential was successfully decoded, but its decode time is later than its encode time by more than its TTL. The clocks on the encoding and decoding hosts could be out of sync.

• EMUNGE_CRED_REWOUND
  The credential was successfully decoded, but its decode time is earlier than its encode time by more than its TTL. The clocks on the encoding and decoding hosts are out of sync.

• EMUNGE_CRED_REPLAYED
  The credential was successfully decoded, but it has been previously decoded on this host within its TTL skew.

• EMUNGE_CRED_UNAUTHORIZED
  The client is not authorized to decode the credential based upon the effective user and/or group ID of the process.

Example

The following example program illustrates the use of a MUNGE credential to ascertain the effective user and group ID of the encoding process.

  #include <stdio.h>
  #include <stdlib.h>
  #include <unistd.h>
  #include <munge.h>

  int
  main (int argc, char *argv[])
  {
      char *cred;
      munge_err_t err;
      uid_t uid;
      gid_t gid;

      err = munge_encode (&cred, NULL, NULL, 0);

      if (err != EMUNGE_SUCCESS) {
          fprintf (stderr, "Error: Failed to encode credential: %s\n",
                  munge_strerror (err));
          exit (EXIT_FAILURE);
      }
      err = munge_decode (cred, NULL, NULL, NULL, &uid, &gid);

      if (err != EMUNGE_SUCCESS) {
          fprintf (stderr, "ERROR: %s\n", munge_strerror (err));
          exit (EXIT_SUCCESS);
      }
      printf ("uid=%d gid=%d\n", uid, gid);
      free (cred);
      exit (0);
  }

Notes

Both munge_encode() and munge_decode() may allocate memory that the caller is responsible for freeing. Failure to do so will result in a memory leak.