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