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// +build linuxacl
#include "permission_linuxacl.h"
#ifdef DEBUG
void debug_print_checker(struct permission_checker *pc) {
fprintf(stderr, "DEBUG: user_name:%s (%d)\n",
pc->user_name, pc->uid);
fprintf(stderr, "DEBUG: ngids:%d\n", pc->ngids);
int j;
for (j = 0; j < pc->ngids; j++) {
fprintf(stderr, "DEBUG: %d", pc->gids[j]);
struct group *gr = getgrgid(pc->gids[j]);
if (gr != NULL)
fprintf(stderr, " (%s)", gr->gr_name);
fprintf(stderr, "\n");
}
fprintf(stderr, "DEBUG: file_path:%s (%d:%d)\n",
pc->file_path, pc->file_stat.st_uid, pc->file_stat.st_gid);
}
#endif // DEBUG
int stat_file(struct permission_checker *pc) {
if (stat(pc->file_path, &pc->file_stat) != 0)
return -1;
#ifdef DEBUG
fprintf(stderr, "DEBUG: File'%s' is owned by '%d:%d'\n",
pc->file_path, pc->file_stat.st_uid, pc->file_stat.st_gid);
#endif
return 0;
}
int get_user_uid(struct permission_checker *pc) {
struct passwd *result = NULL;
size_t bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
if (bufsize == -1)
bufsize = 16384;
char *buf = malloc(bufsize);
if (buf == NULL) {
#ifdef DEBUG
fprintf(stderr, "DEBUG: Unabel to allocate bufer while retrieving user '%s'\n", pc->user_name);
#endif
return -1;
}
int rc = getpwnam_r(pc->user_name, &pc->pw, buf, bufsize, &result);
if (result == NULL) {
#ifdef DEBUG
if (rc == 0) {
fprintf(stderr, "DEBUG: No user '%s' found\n", pc->user_name);
} else {
fprintf(stderr, "DEBUG: Unknown error while retrieving user '%s'\n", pc->user_name);
}
#endif
free(buf);
return -1;
}
pc->uid = pc->pw.pw_uid;
free(buf);
return 0;
}
int get_user_groups(struct permission_checker *pc) {
// First assume we are in 10 groups max
pc->ngids = 10;
pc->gids = malloc(pc->ngids * sizeof(gid_t));
if (pc->gids == NULL) {
#ifdef DEBUG
fprintf(stderr, "DEBUG: Unable to allocate space for gids.");
#endif
return -1;
}
// Try so many times to load group list until it fits into group array.
while (getgrouplist(pc->user_name, pc->pw.pw_gid, pc->gids, &pc->ngids) == -1) {
// Too many groups, enlarge group array and try again
int newngids = pc->ngids + 100;
size_t newsize = newngids * sizeof(gid_t);
if (SIZE_MAX / newngids < sizeof(gid_t)) {
// Overflow
#ifdef DEBUG
fprintf(stderr, "DEBUG: Overflow detected.");
#endif
return -1;
}
gid_t *newgids = realloc(pc->gids, newsize);
if (newgids == NULL) {
#ifdef DEBUG
fprintf(stderr, "DEBUG: Unable to allocate space for gids.");
#endif
free(pc->gids);
return -1;
}
pc->gids = newgids;
pc->ngids = newngids;
}
return 0;
}
int is_member_of_group(struct permission_checker *pc, gid_t gid) {
int j;
for (j = 0; j < pc->ngids; j++)
if (pc->gids[j] == gid)
return 1;
return 0;
}
int check_acl_uid_matches(uid_t uid, acl_entry_t entry) {
int ret = -1;
uid_t *acl_uid = acl_get_qualifier(entry);
if (acl_uid == NULL) {
#ifdef DEBUG
fprintf(stderr, "DEBUG: Unable to retrieve user uid from ACL entry");
#endif
return -1;
}
ret = *acl_uid == uid ? 0 : -1;
#ifdef DEBUG
fprintf(stderr, "DEBUG: ACL user match?: %d <=> %d: %d\n", *acl_uid, uid, ret);
#endif
acl_free(acl_uid);
return ret;
}
int check_acl_gid_matches(gid_t *gids, int ngids, acl_entry_t entry) {
int ret = -1;
gid_t *acl_gid = acl_get_qualifier(entry);
if (acl_gid == NULL) {
#ifdef DEBUG
fprintf(stderr, "DEBUG: Unable to retrieve user uid from ACL entry");
#endif
return -1;
}
int j;
for (j = 0; j < ngids; j++) {
if (*acl_gid == gids[j]) {
#ifdef DEBUG
fprintf(stderr, "DEBUG: User is in group %d", *acl_gid);
#endif
ret = 0;
break;
}
}
#ifdef DEBUG
fprintf(stderr, "DEBUG: ACL group match?: %d <=> ...: %d\n", *acl_gid, ret);
#endif
acl_free(acl_gid);
return ret;
}
int check_acl(struct permission_checker *pc, const int flag) {
// By default user has no read perm.
int has_read_perm = 0;
// By default mask tells that there are read perm. However in order to have
// read permissions both, has_read_perm and mask_allows_read_access must be 1!
int mask_allows_read_access = 1;
acl_type_t type = ACL_TYPE_ACCESS;
acl_t acl = acl_get_file(pc->file_path, type);
if (acl == NULL)
// Unable to retrieve ACL.
return -1;
// Walk through each entry of this ACL.
int id;
for (id = ACL_FIRST_ENTRY; ; id = ACL_NEXT_ENTRY) {
acl_entry_t entry;
if (acl_get_entry(acl, id, &entry) != 1)
// No more ACL entries.
break;
acl_tag_t tag;
if (acl_get_tag_type(entry, &tag) == -1)
// Unable to retrieve ACL tag.
return -1;
switch (tag) {
case ACL_USER_OBJ:
if (flag == GROUP_CHECK)
continue;
#ifdef DEBUG
fprintf(stderr, "DEBUG: ACL_USER_OBJ\n");
#endif
// Ignore this ACL entry if user is not owner of file.
if (pc->uid != pc->file_stat.st_uid)
continue;
break;
case ACL_USER:
if (flag == GROUP_CHECK)
continue;
#ifdef DEBUG
fprintf(stderr, "DEBUG: ACL_USER\n");
#endif
// Ignore this ACL entry if uid does not match.
if (check_acl_uid_matches(pc->uid, entry) != 0)
continue;
break;
case ACL_GROUP_OBJ:
if (flag == USER_CHECK)
continue;
#ifdef DEBUG
fprintf(stderr, "DEBUG: ACL_GROUP_OBJ\n");
#endif
// Ignore ACL entry if user is not in group of file.
if (!is_member_of_group(pc, pc->file_stat.st_gid))
continue;
break;
case ACL_GROUP:
if (flag == USER_CHECK)
continue;
#ifdef DEBUG
fprintf(stderr, "DEBUG: ACL_GROUP\n");
#endif
// Ignore ACL entry if user is not in group of entry.
if (check_acl_gid_matches(pc->gids, pc->ngids, entry) != 0)
continue;
break;
case ACL_OTHER:
if (flag == GROUP_CHECK)
continue;
#ifdef DEBUG
fprintf(stderr, "DEBUG: ACL_OTHER\n");
#endif
break;
case ACL_MASK:
#ifdef DEBUG
fprintf(stderr, "DEBUG: ACL_MASK\n");
#endif
break;
default:
#ifdef DEBUG
fprintf(stderr, "DEBUG: Unknown ACL tag\n");
#endif
return -1;
}
#ifdef DEBUG
fprintf(stderr, "DEBUG: Retrieving permset\n");
#endif
acl_permset_t permset;
int permission;
if (acl_get_permset(entry, &permset) == -1)
// Unable to retrieve permset.
return -1;
if ((permission = acl_get_perm(permset, ACL_READ)) == -1)
// Unable to retrieve permset value.
return -1;
if (permission == 1 && tag != ACL_MASK) {
#ifdef DEBUG
fprintf(stderr, "DEBUG: ACL says user has permission to read file.\n");
#endif
has_read_perm = 1;
} else if (permission == 0 && tag == ACL_MASK) {
// Mask says that there are no permissions to read.
mask_allows_read_access = 0;
#ifdef DEBUG
fprintf(stderr, "DEBUG: ACL mask says no permission to read file.\n");
#endif
}
}
if (has_read_perm && mask_allows_read_access) {
#ifdef DEBUG
fprintf(stderr, "DEBUG: ACL end result: User has permission to read file.\n");
#endif
return 1;
}
#ifdef DEBUG
fprintf(stderr, "DEBUG: ACL end result: User has no permission to read file.\n");
#endif
return 0;
}
int check_traditional(struct permission_checker *pc, const int flag) {
mode_t mode = pc->file_stat.st_mode;
uid_t uid = pc->file_stat.st_uid;
gid_t gid = pc->file_stat.st_gid;
if (flag == USER_CHECK && (mode & S_IROTH)) {
#ifdef DEBUG
fprintf(stderr, "DEBUG: Others can read file '%s'\n",
pc->file_path);
#endif
return 1;
} else if (flag == USER_CHECK && (mode & S_IRUSR) && uid == pc->uid) {
#ifdef DEBUG
fprintf(stderr, "DEBUG: User '%s' can read file '%s'\n",
pc->user_name, pc->file_path);
#endif
return 1;
} else if (flag == GROUP_CHECK && (mode & S_IRGRP) && is_member_of_group(pc, gid)) {
#ifdef DEBUG
fprintf(stderr, "DEBUG: User's '%s' group can read file '%s'\n",
pc->user_name, pc->file_path);
#endif
return 1;
}
return 0;
}
int permission_to_read(char* user_name, char *file_path) {
int rc = -1;
#ifdef DEBUG
fprintf(stderr, "DEBUG: User check '%s' for file '%s'\n", user_name, file_path);
#endif
struct permission_checker pc = {
.user_name = user_name,
.gids = NULL,
.ngids = 0,
.file_path = file_path,
};
// Gather user's UID.
if ((rc = get_user_uid(&pc)) == -1)
// Could not retrieve UID.
goto cleanup;
// Gather file owner (user and group).
if ((rc = stat_file(&pc)) == -1)
// Could not stat file.
goto cleanup;
// Check whether there is an ACL entry which would allow the user
// to read the file. Don't check for any groups yet. The issue with
// groups is that it can be very slow to retrieve the list of groups
// of a specific user when done via a remote LDAP server!
if ((rc = check_acl(&pc, USER_CHECK)) == 1)
// Yes, has permissions.
goto cleanup;
// Check whether ACLs of file could be retrieved.
if (rc == -1) {
if (errno != ENOTSUP)
// Unknown error.
goto cleanup;
// File system does not support ACLs.
// Fallback to traditional permissions.
if ((rc = check_traditional(&pc, USER_CHECK)) == 1)
// Yes, has traditional permissions.
goto cleanup;
if ((rc = get_user_groups(&pc)) == -1)
// Can not retrieve user's groups.
goto cleanup;
rc = check_traditional(&pc, GROUP_CHECK);
goto cleanup;
}
if ((rc = get_user_groups(&pc)) == -1)
// Can not retrieve use'r groups.
goto cleanup;
// Check whether there is an ACL entry which would allow any of the
// user's groups to read the file.
rc = check_acl(&pc, GROUP_CHECK);
cleanup:
#ifdef DEBUG
debug_print_checker(&pc);
#endif
if (pc.ngids)
free(pc.gids);
return rc;
}
// vim: set tabstop=8 softtabstop=0 expandtab shiftwidth=4 smarttab
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