minix/servers/vfs/protect.c
2012-03-25 21:58:14 +02:00

276 lines
7.8 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 "path.h"
#include "param.h"
#include <minix/vfsif.h>
#include "vnode.h"
#include "vmnt.h"
/*===========================================================================*
* do_chmod *
*===========================================================================*/
int do_chmod()
{
/* Perform the chmod(name, mode) and fchmod(fd, mode) system calls. */
struct filp *flp;
struct vnode *vp;
struct vmnt *vmp;
int r;
mode_t new_mode;
char fullpath[PATH_MAX];
struct lookup resolve;
flp = NULL;
lookup_init(&resolve, fullpath, PATH_NOFLAGS, &vmp, &vp);
resolve.l_vmnt_lock = VMNT_WRITE;
resolve.l_vnode_lock = VNODE_WRITE;
if (call_nr == CHMOD) {
/* Temporarily open the file */
if (fetch_name(m_in.name, m_in.name_length, M3, fullpath) != OK)
return(err_code);
if ((vp = eat_path(&resolve, fp)) == NULL) 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, VNODE_WRITE)) == NULL)
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 (r == OK) {
/* Now make the change. Clear setgid bit if file is not in caller's
* group */
if (fp->fp_effuid != SU_UID && vp->v_gid != fp->fp_effgid)
m_in.mode &= ~I_SET_GID_BIT;
r = req_chmod(vp->v_fs_e, vp->v_inode_nr, m_in.mode, &new_mode);
if (r == OK)
vp->v_mode = new_mode;
}
if (call_nr == CHMOD) {
unlock_vnode(vp);
unlock_vmnt(vmp);
} else { /* FCHMOD */
unlock_filp(flp);
}
put_vnode(vp);
return(r);
}
/*===========================================================================*
* do_chown *
*===========================================================================*/
int do_chown()
{
/* Perform the chown(path, owner, group) and fchmod(fd, owner, group) system
* calls. */
struct filp *flp;
struct vnode *vp;
struct vmnt *vmp;
int r;
uid_t uid;
gid_t gid;
mode_t new_mode;
char fullpath[PATH_MAX];
struct lookup resolve;
flp = NULL;
lookup_init(&resolve, fullpath, PATH_NOFLAGS, &vmp, &vp);
resolve.l_vmnt_lock = VMNT_WRITE;
resolve.l_vnode_lock = VNODE_WRITE;
if (call_nr == CHOWN) {
/* Temporarily open the file. */
if (fetch_name(m_in.name1, m_in.name1_length, M1, fullpath) != OK)
return(err_code);
if ((vp = eat_path(&resolve, fp)) == NULL) 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, VNODE_WRITE)) == NULL)
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 (uid > UID_MAX || gid > GID_MAX)
r = EINVAL;
else 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;
}
}
if (call_nr == CHOWN) {
unlock_vnode(vp);
unlock_vmnt(vmp);
} else { /* FCHOWN */
unlock_filp(flp);
}
put_vnode(vp);
return(r);
}
/*===========================================================================*
* do_umask *
*===========================================================================*/
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 *
*===========================================================================*/
int do_access()
{
/* Perform the access(name, mode) system call. */
int r;
struct vnode *vp;
struct vmnt *vmp;
char fullpath[PATH_MAX];
struct lookup resolve;
lookup_init(&resolve, fullpath, PATH_NOFLAGS, &vmp, &vp);
resolve.l_vmnt_lock = VMNT_READ;
resolve.l_vnode_lock = VNODE_READ;
/* 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, fullpath) != OK)
return(err_code);
if ((vp = eat_path(&resolve, fp)) == NULL) return(err_code);
r = forbidden(fp, vp, m_in.mode);
unlock_vnode(vp);
unlock_vmnt(vmp);
put_vnode(vp);
return(r);
}
/*===========================================================================*
* forbidden *
*===========================================================================*/
int forbidden(struct fproc *rfp, 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 ? rfp->fp_realuid : rfp->fp_effuid);
gid = (call_nr == ACCESS ? rfp->fp_realgid : rfp->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(fp, 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);
}
/*===========================================================================*
* read_only *
*===========================================================================*/
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.
*/
return((vp->v_vmnt->m_flags & VMNT_READONLY) ? EROFS : OK);
}