authz.c   [plain text]

/* authz.c : path-based access control
 *
 * ====================================================================
 * Copyright (c) 2000-2006 CollabNet.  All rights reserved.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution.  The terms
 * are also available at http://subversion.tigris.org/license-1.html.
 * If newer versions of this license are posted there, you may use a
 * newer version instead, at your option.
 *
 * This software consists of voluntary contributions made by many
 * individuals.  For exact contribution history, see the revision
 * history and logs, available at http://subversion.tigris.org/.
 * ====================================================================
 */


/*** Includes. ***/

#include <apr_pools.h>
#include <apr_file_io.h>

#include "svn_pools.h"
#include "svn_error.h"
#include "svn_path.h"
#include "svn_repos.h"
#include "svn_config.h"
#include "svn_ctype.h"


/*** Structures. ***/

/* Information for the config enumerators called during authz
   lookup. */
struct authz_lookup_baton {
  /* The authz configuration. */
  svn_config_t *config;

  /* The user to authorize. */
  const char *user;

  /* Explicitly granted rights. */
  svn_repos_authz_access_t allow;
  /* Explicitly denied rights. */
  svn_repos_authz_access_t deny;

  /* The rights required by the caller of the lookup. */
  svn_repos_authz_access_t required_access;

  /* The following are used exclusively in recursive lookups. */

  /* The path in the repository to authorize. */
  const char *repos_path;
  /* repos_path prefixed by the repository name. */
  const char *qualified_repos_path;

  /* Whether, at the end of a recursive lookup, access is granted. */
  svn_boolean_t access;
};

/* Information for the config enumeration functions called during the
   validation process. */
struct authz_validate_baton {
  svn_config_t *config; /* The configuration file being validated. */
  svn_error_t *err;     /* The error being thrown out of the
                           enumerator, if any. */
};

/* Currently this structure is just a wrapper around a
   svn_config_t. */
struct svn_authz_t
{
  svn_config_t *cfg;
};



/*** Checking access. ***/

/* Determine whether the REQUIRED access is granted given what authz
 * to ALLOW or DENY.  Return TRUE if the REQUIRED access is
 * granted.
 *
 * Access is granted either when no required access is explicitly
 * denied (implicit grant), or when the required access is explicitly
 * granted, overriding any denials.
 */
static svn_boolean_t
authz_access_is_granted(svn_repos_authz_access_t allow,
                        svn_repos_authz_access_t deny,
                        svn_repos_authz_access_t required)
{
  svn_repos_authz_access_t stripped_req =
    required & (svn_authz_read | svn_authz_write);

  if ((deny & required) == svn_authz_none)
    return TRUE;
  else if ((allow & required) == stripped_req)
    return TRUE;
  else
    return FALSE;
}


/* Decide whether the REQUIRED access has been conclusively
 * determined.  Return TRUE if the given ALLOW/DENY authz are
 * conclusive regarding the REQUIRED authz.
 *
 * Conclusive determination occurs when any of the REQUIRED authz are
 * granted or denied by ALLOW/DENY.
 */
static svn_boolean_t
authz_access_is_determined(svn_repos_authz_access_t allow,
                           svn_repos_authz_access_t deny,
                           svn_repos_authz_access_t required)
{
  if ((deny & required) || (allow & required))
    return TRUE;
  else
    return FALSE;
}

/* Return TRUE is USER equals ALIAS. The alias definitions are in the
   "aliases" sections of CFG. Use POOL for temporary allocations during
   the lookup. */
static svn_boolean_t
authz_alias_is_user(svn_config_t *cfg,
                    const char *alias,
                    const char *user,
                    apr_pool_t *pool)
{
  const char *value;

  svn_config_get(cfg, &value, "aliases", alias, NULL);
  if (!value)
    return FALSE;

  if (strcmp(value, user) == 0)
    return TRUE;

  return FALSE;
}


/* Return TRUE if USER is in GROUP.  The group definitions are in the
   "groups" section of CFG.  Use POOL for temporary allocations during
   the lookup. */
static svn_boolean_t
authz_group_contains_user(svn_config_t *cfg,
                          const char *group,
                          const char *user,
                          apr_pool_t *pool)
{
  const char *value;
  apr_array_header_t *list;
  int i;

  svn_config_get(cfg, &value, "groups", group, NULL);

  list = svn_cstring_split(value, ",", TRUE, pool);

  for (i = 0; i < list->nelts; i++)
    {
      const char *group_user = APR_ARRAY_IDX(list, i, char *);

      /* If the 'user' is a subgroup, recurse into it. */
      if (*group_user == '@')
        {
          if (authz_group_contains_user(cfg, &group_user[1],
                                        user, pool))
            return TRUE;
        }

      /* If the 'user' is an alias, verify it. */
      else if (*group_user == '&')
        {
          if (authz_alias_is_user(cfg, &group_user[1],
                                  user, pool))
            return TRUE;
        }

      /* If the user matches, stop. */
      else if (strcmp(user, group_user) == 0)
        return TRUE;
    }

  return FALSE;
}


/* Determines whether an authz rule applies to the current
 * user, given the name part of the rule's name-value pair
 * in RULE_MATCH_STRING and the authz_lookup_baton object
 * B with the username in question.
 */
static svn_boolean_t
authz_line_applies_to_user(const char *rule_match_string,
                           struct authz_lookup_baton *b,
                           apr_pool_t *pool)
{
  /* If the rule has an inversion, recurse and invert the result. */
  if (rule_match_string[0] == '~')
    return !authz_line_applies_to_user(&rule_match_string[1], b, pool);

  /* Check for special tokens. */
  if (strcmp(rule_match_string, "$anonymous") == 0)
    return (b->user == NULL);
  if (strcmp(rule_match_string, "$authenticated") == 0)
    return (b->user != NULL);

  /* Check for a wildcard rule. */
  if (strcmp(rule_match_string, "*") == 0)
    return TRUE;

  /* If we get here, then the rule is:
   *  - Not an inversion rule.
   *  - Not an authz token rule.
   *  - Not a wildcard rule.
   *
   * All that's left over is regular user or group specifications.
   */

  /* If the session is anonymous, then a user/group
   * rule definitely won't match.
   */
  if (b->user == NULL)
    return FALSE;

  /* Process the rule depending on whether it is
   * a user, alias or group rule.
   */
  if (rule_match_string[0] == '@')
    return authz_group_contains_user(
      b->config, &rule_match_string[1], b->user, pool);
  else if (rule_match_string[0] == '&')
    return authz_alias_is_user(
      b->config, &rule_match_string[1], b->user, pool);
  else
    return (strcmp(b->user, rule_match_string) == 0);
}


/* Callback to parse one line of an authz file and update the
 * authz_baton accordingly.
 */
static svn_boolean_t
authz_parse_line(const char *name, const char *value,
                 void *baton, apr_pool_t *pool)
{
  struct authz_lookup_baton *b = baton;

  /* Stop if the rule doesn't apply to this user. */
  if (!authz_line_applies_to_user(name, b, pool))
    return TRUE;

  /* Set the access grants for the rule. */
  if (strchr(value, 'r'))
    b->allow |= svn_authz_read;
  else
    b->deny |= svn_authz_read;

  if (strchr(value, 'w'))
    b->allow |= svn_authz_write;
  else
    b->deny |= svn_authz_write;

  return TRUE;
}


/* Callback to parse a section and update the authz_baton if the
 * section denies access to the subtree the baton describes.
 */
static svn_boolean_t
authz_parse_section(const char *section_name, void *baton, apr_pool_t *pool)
{
  struct authz_lookup_baton *b = baton;
  svn_boolean_t conclusive;

  /* Does the section apply to us? */
  if (svn_path_is_ancestor(b->qualified_repos_path,
                           section_name) == FALSE
      && svn_path_is_ancestor(b->repos_path,
                              section_name) == FALSE)
    return TRUE;

  /* Work out what this section grants. */
  b->allow = b->deny = 0;
  svn_config_enumerate2(b->config, section_name,
                        authz_parse_line, b, pool);

  /* Has the section explicitly determined an access? */
  conclusive = authz_access_is_determined(b->allow, b->deny,
                                          b->required_access);

  /* Is access granted OR inconclusive? */
  b->access = authz_access_is_granted(b->allow, b->deny,
                                      b->required_access)
    || !conclusive;

  /* As long as access isn't conclusively denied, carry on. */
  return b->access;
}


/* Validate access to the given user for the given path.  This
 * function checks rules for exactly the given path, and first tries
 * to access a section specific to the given repository before falling
 * back to pan-repository rules.
 *
 * Update *access_granted to inform the caller of the outcome of the
 * lookup.  Return a boolean indicating whether the access rights were
 * successfully determined.
 */
static svn_boolean_t
authz_get_path_access(svn_config_t *cfg, const char *repos_name,
                      const char *path, const char *user,
                      svn_repos_authz_access_t required_access,
                      svn_boolean_t *access_granted,
                      apr_pool_t *pool)
{
  const char *qualified_path;
  struct authz_lookup_baton baton = { 0 };

  baton.config = cfg;
  baton.user = user;

  /* Try to locate a repository-specific block first. */
  qualified_path = apr_pstrcat(pool, repos_name, ":", path, NULL);
  svn_config_enumerate2(cfg, qualified_path,
                        authz_parse_line, &baton, pool);

  *access_granted = authz_access_is_granted(baton.allow, baton.deny,
                                            required_access);

  /* If the first test has determined access, stop now. */
  if (authz_access_is_determined(baton.allow, baton.deny,
                                 required_access))
    return TRUE;

  /* No repository specific rule, try pan-repository rules. */
  svn_config_enumerate2(cfg, path, authz_parse_line, &baton, pool);

  *access_granted = authz_access_is_granted(baton.allow, baton.deny,
                                            required_access);
  return authz_access_is_determined(baton.allow, baton.deny,
                                    required_access);
}


/* Validate access to the given user for the subtree starting at the
 * given path.  This function walks the whole authz file in search of
 * rules applying to paths in the requested subtree which deny the
 * requested access.
 *
 * As soon as one is found, or else when the whole ACL file has been
 * searched, return the updated authorization status.
 */
static svn_boolean_t
authz_get_tree_access(svn_config_t *cfg, const char *repos_name,
                      const char *path, const char *user,
                      svn_repos_authz_access_t required_access,
                      apr_pool_t *pool)
{
  struct authz_lookup_baton baton = { 0 };

  baton.config = cfg;
  baton.user = user;
  baton.required_access = required_access;
  baton.repos_path = path;
  baton.qualified_repos_path = apr_pstrcat(pool, repos_name,
                                           ":", path, NULL);
  /* Default to access granted if no rules say otherwise. */
  baton.access = TRUE;

  svn_config_enumerate_sections2(cfg, authz_parse_section,
                                 &baton, pool);

  return baton.access;
}


/* Callback to parse sections of the configuration file, looking for
   any kind of granted access.  Implements the
   svn_config_section_enumerator2_t interface. */
static svn_boolean_t
authz_global_parse_section(const char *section_name, void *baton,
                           apr_pool_t *pool)
{
  struct authz_lookup_baton *b = baton;

  /* Does the section apply to the query? */
  if (section_name[0] == '/'
      || strncmp(section_name, b->repos_path,
                 strlen(b->repos_path)) == 0)
    {
      b->allow = b->deny = svn_authz_none;

      svn_config_enumerate2(b->config, section_name,
                            authz_parse_line, baton, pool);
      b->access = authz_access_is_granted(b->allow, b->deny,
                                          b->required_access);

      /* Continue as long as we don't find a determined, granted access. */
      return !(b->access
               && authz_access_is_determined(b->allow, b->deny,
                                             b->required_access));
    }

  return TRUE;
}


/* Walk through the authz CFG to check if USER has the REQUIRED_ACCESS
 * to any path within the REPOSITORY.  Return TRUE if so.  Use POOL
 * for temporary allocations. */
static svn_boolean_t
authz_get_global_access(svn_config_t *cfg, const char *repos_name,
                        const char *user,
                        svn_repos_authz_access_t required_access,
                        apr_pool_t *pool)
{
  struct authz_lookup_baton baton = { 0 };

  baton.config = cfg;
  baton.user = user;
  baton.required_access = required_access;
  baton.access = FALSE; /* Deny access by default. */
  baton.repos_path = apr_pstrcat(pool, repos_name, ":/", NULL);

  svn_config_enumerate_sections2(cfg, authz_global_parse_section,
                                 &baton, pool);

  /* If walking the configuration was inconclusive, deny access. */
  if (!authz_access_is_determined(baton.allow,
                                  baton.deny, baton.required_access))
    return FALSE;

  return baton.access;
}



/*** Validating the authz file. ***/

/* Check for errors in GROUP's definition of CFG.  The errors
 * detected are references to non-existent groups and circular
 * dependencies between groups.  If an error is found, return
 * SVN_ERR_AUTHZ_INVALID_CONFIG.  Use POOL for temporary
 * allocations only.
 *
 * CHECKED_GROUPS should be an empty (it is used for recursive calls).
 */
static svn_error_t *
authz_group_walk(svn_config_t *cfg,
                 const char *group,
                 apr_hash_t *checked_groups,
                 apr_pool_t *pool)
{
  const char *value;
  apr_array_header_t *list;
  int i;

  svn_config_get(cfg, &value, "groups", group, NULL);
  /* Having a non-existent group in the ACL configuration might be the
     sign of a typo.  Refuse to perform authz on uncertain rules. */
  if (!value)
    return svn_error_createf(SVN_ERR_AUTHZ_INVALID_CONFIG, NULL,
                             "An authz rule refers to group '%s', "
                             "which is undefined",
                             group);

  list = svn_cstring_split(value, ",", TRUE, pool);

  for (i = 0; i < list->nelts; i++)
    {
      const char *group_user = APR_ARRAY_IDX(list, i, char *);

      /* If the 'user' is a subgroup, recurse into it. */
      if (*group_user == '@')
        {
          /* A circular dependency between groups is a Bad Thing.  We
             don't do authz with invalid ACL files. */
          if (apr_hash_get(checked_groups, &group_user[1],
                           APR_HASH_KEY_STRING))
            return svn_error_createf(SVN_ERR_AUTHZ_INVALID_CONFIG,
                                     NULL,
                                     "Circular dependency between "
                                     "groups '%s' and '%s'",
                                     &group_user[1], group);

          /* Add group to hash of checked groups. */
          apr_hash_set(checked_groups, &group_user[1],
                       APR_HASH_KEY_STRING, "");

          /* Recurse on that group. */
          SVN_ERR(authz_group_walk(cfg, &group_user[1],
                                   checked_groups, pool));

          /* Remove group from hash of checked groups, so that we don't
             incorrectly report an error if we see it again as part of
             another group. */
          apr_hash_set(checked_groups, &group_user[1],
                       APR_HASH_KEY_STRING, NULL);
        }
      else if (*group_user == '&')
        {
          const char *alias;

          svn_config_get(cfg, &alias, "aliases", &group_user[1], NULL);
          /* Having a non-existent alias in the ACL configuration might be the
             sign of a typo.  Refuse to perform authz on uncertain rules. */
          if (!alias)
            return svn_error_createf(SVN_ERR_AUTHZ_INVALID_CONFIG, NULL,
                                     "An authz rule refers to alias '%s', "
                                     "which is undefined",
                                     &group_user[1]);
        }
    }

  return SVN_NO_ERROR;
}


/* Callback to perform some simple sanity checks on an authz rule.
 *
 * - If RULE_MATCH_STRING references a group or an alias, verify that
 *   the group or alias definition exists.
 * - If RULE_MATCH_STRING specifies a token (starts with $), verify
 *   that the token name is valid.
 * - If RULE_MATCH_STRING is using inversion, verify that it isn't
 *   doing it more than once within the one rule, and that it isn't
 *   "~*", as that would never match.
 * - Check that VALUE part of the rule specifies only allowed rule
 *   flag characters ('r' and 'w').
 *
 * Return TRUE if the rule has no errors. Use BATON for context and
 * error reporting.
 */
static svn_boolean_t authz_validate_rule(const char *rule_match_string,
                                         const char *value,
                                         void *baton,
                                         apr_pool_t *pool)
{
  const char *val;
  const char *match = rule_match_string;
  struct authz_validate_baton *b = baton;

  /* Make sure the user isn't using double-negatives. */
  if (match[0] == '~')
    {
      /* Bump the pointer past the inversion for the other checks. */
      match++;

      /* Another inversion is a double negative; we can't not stop. */
      if (match[0] == '~')
        {
          b->err = svn_error_createf(SVN_ERR_AUTHZ_INVALID_CONFIG, NULL,
                                     "Rule '%s' has more than one "
                                     "inversion; double negatives are "
                                     "not permitted.",
                                     rule_match_string);
          return FALSE;
        }

      /* Make sure that the rule isn't "~*", which won't ever match. */
      if (strcmp(match, "*") == 0)
        {
          b->err = svn_error_create(SVN_ERR_AUTHZ_INVALID_CONFIG, NULL,
                                    "Authz rules with match string '~*' "
                                    "are not allowed, because they never "
                                    "match anyone.");
          return FALSE;
        }
    }

  /* If the rule applies to a group, check its existence. */
  if (match[0] == '@')
    {
      const char *group = &match[1];

      svn_config_get(b->config, &val, "groups", group, NULL);

      /* Having a non-existent group in the ACL configuration might be
         the sign of a typo.  Refuse to perform authz on uncertain
         rules. */
      if (!val)
        {
          b->err = svn_error_createf(SVN_ERR_AUTHZ_INVALID_CONFIG, NULL,
                                     "An authz rule refers to group "
                                     "'%s', which is undefined",
                                     rule_match_string);
          return FALSE;
        }
    }

  /* If the rule applies to an alias, check its existence. */
  if (match[0] == '&')
    {
      const char *alias = &match[1];

      svn_config_get(b->config, &val, "aliases", alias, NULL);

      if (!val)
        {
          b->err = svn_error_createf(SVN_ERR_AUTHZ_INVALID_CONFIG, NULL,
                                     "An authz rule refers to alias "
                                     "'%s', which is undefined",
                                     rule_match_string);
          return FALSE;
        }
     }

  /* If the rule specifies a token, check its validity. */
  if (match[0] == '$')
    {
      const char *token_name = &match[1];

      if ((strcmp(token_name, "anonymous") != 0)
       && (strcmp(token_name, "authenticated") != 0))
        {
          b->err = svn_error_createf(SVN_ERR_AUTHZ_INVALID_CONFIG, NULL,
                                     "Unrecognized authz token '%s'.",
                                     rule_match_string);
          return FALSE;
        }
    }

  val = value;

  while (*val)
    {
      if (*val != 'r' && *val != 'w' && ! svn_ctype_isspace(*val))
        {
          b->err = svn_error_createf(SVN_ERR_AUTHZ_INVALID_CONFIG, NULL,
                                     "The character '%c' in rule '%s' is not "
                                     "allowed in authz rules", *val,
                                     rule_match_string);
          return FALSE;
        }

      ++val;
    }

  return TRUE;
}

/* Callback to check ALIAS's definition for validity.  Use
   BATON for context and error reporting. */
static svn_boolean_t authz_validate_alias(const char *alias,
                                          const char *value,
                                          void *baton,
                                          apr_pool_t *pool)
{
  /* No checking at the moment, every alias is valid */
  return TRUE;
}


/* Callback to check GROUP's definition for cyclic dependancies.  Use
   BATON for context and error reporting. */
static svn_boolean_t authz_validate_group(const char *group,
                                          const char *value,
                                          void *baton,
                                          apr_pool_t *pool)
{
  struct authz_validate_baton *b = baton;

  b->err = authz_group_walk(b->config, group, apr_hash_make(pool), pool);
  if (b->err)
    return FALSE;

  return TRUE;
}


/* Callback to check the contents of the configuration section given
   by NAME.  Use BATON for context and error reporting. */
static svn_boolean_t authz_validate_section(const char *name,
                                            void *baton,
                                            apr_pool_t *pool)
{
  struct authz_validate_baton *b = baton;

  /* If the section is the groups definition, use the group checking
     callback. Otherwise, use the rule checking callback. */
  if (strncmp(name, "groups", 6) == 0)
    svn_config_enumerate2(b->config, name, authz_validate_group,
                          baton, pool);
  else if (strncmp(name, "aliases", 7) == 0)
    svn_config_enumerate2(b->config, name, authz_validate_alias,
                          baton, pool);
  else
    svn_config_enumerate2(b->config, name, authz_validate_rule,
                          baton, pool);

  if (b->err)
    return FALSE;

  return TRUE;
}



/*** Public functions. ***/

svn_error_t *
svn_repos_authz_read(svn_authz_t **authz_p, const char *file,
                     svn_boolean_t must_exist, apr_pool_t *pool)
{
  svn_authz_t *authz = apr_palloc(pool, sizeof(*authz));
  struct authz_validate_baton baton = { 0 };

  baton.err = SVN_NO_ERROR;

  /* Load the rule file. */
  SVN_ERR(svn_config_read(&authz->cfg, file, must_exist, pool));
  baton.config = authz->cfg;

  /* Step through the entire rule file, stopping on error. */
  svn_config_enumerate_sections2(authz->cfg, authz_validate_section,
                                 &baton, pool);
  SVN_ERR(baton.err);

  *authz_p = authz;
  return SVN_NO_ERROR;
}


svn_error_t *
svn_repos_authz_check_access(svn_authz_t *authz, const char *repos_name,
                             const char *path, const char *user,
                             svn_repos_authz_access_t required_access,
                             svn_boolean_t *access_granted,
                             apr_pool_t *pool)
{
  const char *current_path = path;

  /* If PATH is NULL, do a global access lookup. */
  if (!path)
    {
      *access_granted = authz_get_global_access(authz->cfg, repos_name,
                                                user, required_access,
                                                pool);
      return SVN_NO_ERROR;
    }

  /* Determine the granted access for the requested path. */
  while (!authz_get_path_access(authz->cfg, repos_name,
                                current_path, user,
                                required_access,
                                access_granted,
                                pool))
    {
      /* Stop if the loop hits the repository root with no
         results. */
      if (current_path[0] == '/' && current_path[1] == '\0')
        {
          /* Deny access by default. */
          *access_granted = FALSE;
          return SVN_NO_ERROR;
        }

      /* Work back to the parent path. */
      svn_path_split(current_path, &current_path, NULL, pool);
    }

  /* If the caller requested recursive access, we need to walk through
     the entire authz config to see whether any child paths are denied
     to the requested user. */
  if (*access_granted && (required_access & svn_authz_recursive))
    *access_granted = authz_get_tree_access(authz->cfg, repos_name, path,
                                            user, required_access, pool);

  return SVN_NO_ERROR;
}