NAME

puffs_cred — puffs credential and access control routines

LIBRARY

puffs Convenience Library (libpuffs, -lpuffs)

SYNOPSIS

#include <puffs.h>

int
puffs_cred_getuid(const struct puffs_cred *pcr, uid_t *uid);

int
puffs_cred_getgid(const struct puffs_cred *pcr, gid_t *gid);

int
puffs_cred_getgroups(const struct puffs_cred *pcr, gid_t *gids, short *ngids);

bool
puffs_cred_isuid(const struct puffs_cred *pcr, uid_t uid);

bool
puffs_cred_hasgroup(const struct puffs_cred *pcr, gid_t gid);

bool
puffs_cred_iskernel(const struct puffs_cred *pcr);

bool
puffs_cred_isfs(const struct puffs_cred *pcr);

bool
puffs_cred_isjuggernaut(const struct puffs_cred *pcr);

int
puffs_access(enum vtype type, mode_t file_mode, uid_t owner, gid_t group, mode_t access_mode, const struct puffs_cred *pcr);

int
puffs_access_chown(uid_t owner, gid_t group, uid_t newowner, gid_t newgroup, const struct puffs_cred *pcr);

int
puffs_access_chmod(uid_t owner, gid_t group, enum vtype type, mode_t newmode, const struct puffs_cred *pcr);

int
puffs_access_times(uid_t owner, gid_t group, mode_t file_mode, int va_utimes_null, const struct puffs_cred *pcr);

DESCRIPTION

These functions can be used to check operation credentials and perform access control. The structure struct puffs_cred can contain two types of credentials: ones belonging to users and ones belonging to the kernel. The latter is further divided into generic kernel credentials and file system credentials. The general rule is that these should be treated as more powerful than superuser credentials, but the file system is free to treat them as it sees fit.

Credentials

The puffs_cred_get() family of functions fetch the uid or gid(s) from the given credential cookie. They return 0 for success or -1 for an error and set errno. An error happens when the credentials represent kernel or file system credentials and do not contain an uid or gid(s).

For puffs_cred_getgroups(), the argument gids should point to an array with room for *ngids elements.

The puffs_cred_is() family of functions return 1 if the truth value of the function for pcr is true and 0 if it is false. The function puffs_cred_isjuggernaut() is true if pcr describes superuser, kernel or file system credentials.

Access Control

To help the programmers task of emulating normal kernel file system access control semantics, several helper functions are provided to check if access is allowed. They return 0 if access should be permitted or an errno value to indicate that access should be denied with the returned value.

puffs_access() is equivalent to the kernel vaccess() function. The arguments specify current information of the file to be tested with the exception of access_mode, which is a combination of PUFFS_VREAD, PUFFS_VWRITE and PUFFS_VEXEC indicating the desired file access mode.

The rest of the functions provide UFS semantics for operations. puffs_access_chown() checks if it is permissible to chown a file with the current uid and gid to the new uid and gid with the credentials of pcr.

puffs_access_chmod() checks against permission to chmod a file of type type to the mode newmode.

Finally, puffs_access_times() checks if it is allowable to update the timestamps of a file. The argument va_utimes_null signals if the flags VA_UTIMES_NULL was set in va_vaflags of struct vattr. If coming from a path where this information is unavailable, passing 0 as this argument restricts the permission of modification to the owner and superuser. Otherwise the function checks for write permissions to the node and returns success if the caller has write permissions.