minix/servers/vfs/protect.c

249 lines
7.3 KiB
C

/* This file deals with protection in the file system. It contains the code
* for four system calls that relate to protection.
*
* The entry points into this file are
* do_chmod: perform the CHMOD and FCHMOD system calls
* do_chown: perform the CHOWN and FCHOWN system calls
* do_umask: perform the UMASK system call
* do_access: perform the ACCESS system call
*/
#include "fs.h"
#include <unistd.h>
#include <minix/callnr.h>
#include "file.h"
#include "fproc.h"
#include "param.h"
#include <minix/vfsif.h>
#include "vnode.h"
#include "vmnt.h"
FORWARD _PROTOTYPE( in_group, (gid_t grp) );
/*===========================================================================*
* do_chmod *
*===========================================================================*/
PUBLIC int do_chmod()
{
/* Perform the chmod(name, mode) and fchmod(fd, mode) system calls. */
struct filp *flp;
struct vnode *vp;
int r;
mode_t new_mode;
if (call_nr == CHMOD) {
/* Temporarily open the file */
if(fetch_name(m_in.name, m_in.name_length, M3) != OK) return(err_code);
if ((vp = eat_path(PATH_NOFLAGS)) == NIL_VNODE) return(err_code);
} else { /* call_nr == FCHMOD */
/* File is already opened; get a pointer to vnode from filp. */
if (!(flp = get_filp(m_in.fd))) return(err_code);
vp = flp->filp_vno;
dup_vnode(vp);
}
/* Only the owner or the super_user may change the mode of a file.
* No one may change the mode of a file on a read-only file system.
*/
if (vp->v_uid != fp->fp_effuid && fp->fp_effuid != SU_UID)
r = EPERM;
else
r = read_only(vp);
/* If error, return inode. */
if (r != OK) {
put_vnode(vp);
return(r);
}
/* Now make the change. Clear setgid bit if file is not in caller's grp */
if (fp->fp_effuid != SU_UID && vp->v_gid != fp->fp_effgid)
m_in.mode &= ~I_SET_GID_BIT;
if ((r = req_chmod(vp->v_fs_e, vp->v_inode_nr, m_in.mode, &new_mode)) == OK)
vp->v_mode = new_mode;
put_vnode(vp);
return(OK);
}
/*===========================================================================*
* do_chown *
*===========================================================================*/
PUBLIC int do_chown()
{
/* Perform the chmod(name, mode) and fchmod(fd, mode) system calls. */
struct filp *flp;
struct vnode *vp;
int r;
uid_t uid;
gid_t gid;
mode_t new_mode;
if (call_nr == CHOWN) {
/* Temporarily open the file. */
if(fetch_name(m_in.name1, m_in.name1_length, M1) != OK) return(err_code);
if ((vp = eat_path(PATH_NOFLAGS)) == NIL_VNODE) return(err_code);
} else { /* call_nr == FCHOWN */
/* File is already opened; get a pointer to the vnode from filp. */
if (!(flp = get_filp(m_in.fd))) return(err_code);
vp = flp->filp_vno;
dup_vnode(vp);
}
r = read_only(vp);
if (r == OK) {
/* FS is R/W. Whether call is allowed depends on ownership, etc. */
/* The super user can do anything, so check permissions only if we're
a regular user. */
if (fp->fp_effuid != SU_UID) {
/* Regular users can only change groups of their own files. */
if (vp->v_uid != fp->fp_effuid) r = EPERM;
if (vp->v_uid != m_in.owner) r = EPERM; /* no giving away */
if (fp->fp_effgid != m_in.group) r = EPERM;
}
}
if (r == OK) {
/* Do not change uid/gid if new uid/gid is -1. */
uid = (m_in.owner == (uid_t)-1 ? vp->v_uid : m_in.owner);
gid = (m_in.group == (gid_t)-1 ? vp->v_gid : m_in.group);
if ((r = req_chown(vp->v_fs_e, vp->v_inode_nr, uid, gid,
&new_mode)) == OK) {
vp->v_uid = uid;
vp->v_gid = gid;
vp->v_mode = new_mode;
}
}
put_vnode(vp);
return(r);
}
/*===========================================================================*
* do_umask *
*===========================================================================*/
PUBLIC int do_umask()
{
/* Perform the umask(co_mode) system call. */
register mode_t r;
r = ~fp->fp_umask; /* set 'r' to complement of old mask */
fp->fp_umask = ~(m_in.co_mode & RWX_MODES);
return(r); /* return complement of old mask */
}
/*===========================================================================*
* do_access *
*===========================================================================*/
PUBLIC int do_access()
{
/* Perform the access(name, mode) system call. */
int r;
struct vnode *vp;
/* First check to see if the mode is correct. */
if ( (m_in.mode & ~(R_OK | W_OK | X_OK)) != 0 && m_in.mode != F_OK)
return(EINVAL);
/* Temporarily open the file. */
if (fetch_name(m_in.name, m_in.name_length, M3) != OK) return(err_code);
if ((vp = eat_path(PATH_NOFLAGS)) == NIL_VNODE) return(err_code);
r = forbidden(vp, m_in.mode);
put_vnode(vp);
return(r);
}
/*===========================================================================*
* forbidden *
*===========================================================================*/
PUBLIC int forbidden(struct vnode *vp, mode_t access_desired)
{
/* Given a pointer to an vnode, 'vp', and the access desired, determine
* if the access is allowed, and if not why not. The routine looks up the
* caller's uid in the 'fproc' table. If access is allowed, OK is returned
* if it is forbidden, EACCES is returned.
*/
register mode_t bits, perm_bits;
uid_t uid;
gid_t gid;
int r, shift;
if (vp->v_uid == (uid_t) -1 || vp->v_gid == (gid_t) -1) return(EACCES);
/* Isolate the relevant rwx bits from the mode. */
bits = vp->v_mode;
uid = (call_nr == ACCESS ? fp->fp_realuid : fp->fp_effuid);
gid = (call_nr == ACCESS ? fp->fp_realgid : fp->fp_effgid);
if (uid == SU_UID) {
/* Grant read and write permission. Grant search permission for
* directories. Grant execute permission (for non-directories) if
* and only if one of the 'X' bits is set.
*/
if ( (bits & I_TYPE) == I_DIRECTORY ||
bits & ((X_BIT << 6) | (X_BIT << 3) | X_BIT))
perm_bits = R_BIT | W_BIT | X_BIT;
else
perm_bits = R_BIT | W_BIT;
} else {
if (uid == vp->v_uid) shift = 6; /* owner */
else if (gid == vp->v_gid) shift = 3; /* group */
else if (in_group(vp->v_gid) == OK) shift = 3; /* suppl. groups */
else shift = 0; /* other */
perm_bits = (bits >> shift) & (R_BIT | W_BIT | X_BIT);
}
/* If access desired is not a subset of what is allowed, it is refused. */
r = OK;
if ((perm_bits | access_desired) != perm_bits) r = EACCES;
/* Check to see if someone is trying to write on a file system that is
* mounted read-only.
*/
if (r == OK)
if (access_desired & W_BIT)
r = read_only(vp);
return(r);
}
/*===========================================================================*
* in_group *
*===========================================================================*/
PRIVATE int in_group(gid_t grp)
{
int i;
for (i = 0; i < fp->fp_ngroups; i++)
if (fp->fp_sgroups[i] == grp)
return(OK);
return(EINVAL);
}
/*===========================================================================*
* read_only *
*===========================================================================*/
PUBLIC int read_only(vp)
struct vnode *vp; /* ptr to inode whose file sys is to be cked */
{
/* Check to see if the file system on which the inode 'ip' resides is mounted
* read only. If so, return EROFS, else return OK.
*/
register struct vmnt *mp;
mp = vp->v_vmnt;
return(mp->m_flags ? EROFS : OK);
}