212 lines
6.6 KiB
C
212 lines
6.6 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 system call
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* do_chown: perform the CHOWN system call
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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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* forbidden: check to see if a given access is allowed on a given inode
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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 "buf.h"
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#include "file.h"
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#include "fproc.h"
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#include "inode.h"
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#include "param.h"
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#include "super.h"
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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) system call. */
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register struct inode *rip;
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register int r;
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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 ( (rip = eat_path(user_path)) == NIL_INODE) return(err_code);
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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 (rip->i_uid != fp->fp_effuid && !super_user)
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r = EPERM;
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else
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r = read_only(rip);
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/* If error, return inode. */
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if (r != OK) {
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put_inode(rip);
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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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rip->i_mode = (rip->i_mode & ~ALL_MODES) | (m_in.mode & ALL_MODES);
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if (!super_user && rip->i_gid != fp->fp_effgid)rip->i_mode &= ~I_SET_GID_BIT;
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rip->i_update |= CTIME;
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rip->i_dirt = DIRTY;
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put_inode(rip);
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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 chown(name, owner, group) system call. */
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register struct inode *rip;
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register int r;
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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 ( (rip = eat_path(user_path)) == NIL_INODE) return(err_code);
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/* Not permitted to change the owner of a file on a read-only file sys. */
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r = read_only(rip);
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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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if (super_user) {
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/* The super user can do anything. */
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rip->i_uid = m_in.owner; /* others later */
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} else {
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/* Regular users can only change groups of their own files. */
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if (rip->i_uid != fp->fp_effuid) r = EPERM;
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if (rip->i_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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rip->i_gid = m_in.group;
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rip->i_mode &= ~(I_SET_UID_BIT | I_SET_GID_BIT);
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rip->i_update |= CTIME;
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rip->i_dirt = DIRTY;
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}
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put_inode(rip);
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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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struct inode *rip;
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register int r;
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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 whose access is to be checked. */
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if (fetch_name(m_in.name, m_in.name_length, M3) != OK) return(err_code);
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if ( (rip = eat_path(user_path)) == NIL_INODE) return(err_code);
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/* Now check the permissions. */
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r = forbidden(rip, (mode_t) m_in.mode);
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put_inode(rip);
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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(register struct inode *rip, mode_t access_desired)
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{
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/* Given a pointer to an inode, 'rip', 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 struct inode *old_rip = rip;
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register struct super_block *sp;
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register mode_t bits, perm_bits;
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int r, shift, test_uid, test_gid, type;
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if (rip->i_mount == I_MOUNT) /* The inode is mounted on. */
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for (sp = &super_block[1]; sp < &super_block[NR_SUPERS]; sp++)
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if (sp->s_imount == rip) {
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rip = get_inode(sp->s_dev, ROOT_INODE);
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break;
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} /* if */
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/* Isolate the relevant rwx bits from the mode. */
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bits = rip->i_mode;
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test_uid = (call_nr == ACCESS ? fp->fp_realuid : fp->fp_effuid);
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test_gid = (call_nr == ACCESS ? fp->fp_realgid : fp->fp_effgid);
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if (test_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 (test_uid == rip->i_uid) shift = 6; /* owner */
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else if (test_gid == rip->i_gid ) shift = 3; /* group */
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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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type = rip->i_mode & I_TYPE;
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if (r == OK)
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if (access_desired & W_BIT)
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r = read_only(rip);
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if (rip != old_rip) put_inode(rip);
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return(r);
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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(ip)
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struct inode *ip; /* 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 super_block *sp;
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sp = ip->i_sp;
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return(sp->s_rd_only ? EROFS : OK);
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}
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