minix/lib/libpuffs/puffs_cred.3

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.Dd October 18, 2007
.Dt PUFFS_CRED 3
.Os
.Sh NAME
.Nm puffs_cred
.Nd puffs credential and access control routines
.Sh LIBRARY
.Lb libpuffs
.Sh SYNOPSIS
.In puffs.h
.Ft int
.Fn puffs_cred_getuid "const struct puffs_cred *pcr" "uid_t *uid
.Ft int
.Fn puffs_cred_getgid "const struct puffs_cred *pcr" "gid_t *gid"
.Ft int
.Fo puffs_cred_getgroups
.Fa "const struct puffs_cred *pcr" "gid_t *gids" "short *ngids"
.Fc
.Pp
.Ft bool
.Fn puffs_cred_isuid "const struct puffs_cred *pcr" "uid_t uid"
.Ft bool
.Fn puffs_cred_hasgroup "const struct puffs_cred *pcr" "gid_t gid"
.Ft bool
.Fn puffs_cred_iskernel "const struct puffs_cred *pcr"
.Ft bool
.Fn puffs_cred_isfs "const struct puffs_cred *pcr"
.Ft bool
.Fn puffs_cred_isjuggernaut "const struct puffs_cred *pcr"
.Pp
.Ft int
.Fo puffs_access
.Fa "enum vtype type" "mode_t file_mode" "uid_t owner" "gid_t group"
.Fa "mode_t access_mode" "const struct puffs_cred *pcr"
.Fc
.Ft int
.Fo puffs_access_chown
.Fa "uid_t owner" "gid_t group" "uid_t newowner" "gid_t newgroup"
.Fa "const struct puffs_cred *pcr"
.Fc
.Ft int
.Fo puffs_access_chmod
.Fa "uid_t owner" "gid_t group" "enum vtype type" "mode_t newmode"
.Fa "const struct puffs_cred *pcr"
.Fc
.Ft int
.Fo puffs_access_times
.Fa "uid_t owner" "gid_t group" "mode_t file_mode" "int va_utimes_null"
.Fa "const struct puffs_cred *pcr"
.Fc
.Sh DESCRIPTION
These functions can be used to check operation credentials and perform
access control.
The structure
.Vt 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.
.Ss Credentials
The
.Fn 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
.Va errno .
An error happens when the credentials represent kernel or file system
credentials and do not contain an uid or gid(s).
.Pp
For
.Fn puffs_cred_getgroups ,
the argument
.Fa gids
should point to an array with room for
.Fa *ngids
elements.
.Pp
The
.Fn puffs_cred_is
family of functions return 1 if the truth value of the function for
.Fa pcr
is true and 0 if it is false.
The function
.Fn puffs_cred_isjuggernaut
is true if
.Fa pcr
describes superuser, kernel or file system credentials.
.Ss 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.
.Pp
.Fn puffs_access
is equivalent to the kernel
.Fn vaccess
function.
The arguments specify current information of the file to be
tested with the exception of
.Fa access_mode ,
which is a combination of
.Dv PUFFS_VREAD ,
.Dv PUFFS_VWRITE
and
.Dv PUFFS_VEXEC
indicating the desired file access mode.
.Pp
The rest of the functions provide UFS semantics for operations.
.Fn 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
.Fa pcr .
.Pp
.Fn puffs_access_chmod
checks against permission to chmod a file of type
.Fa type
to the mode
.Fa newmode .
.Pp
Finally,
.Fn puffs_access_times
checks if it is allowable to update the timestamps of a file.
The argument
.Fa va_utimes_null
signals if the flags
.Dv VA_UTIMES_NULL
was set in
.Fa va_vaflags
of
.Va 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.
.Sh SEE ALSO
.Xr puffs 3 ,
.Xr vnode 9