minix/servers/fs/protect.c

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/* 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
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* do_chmod: perform the CHMOD and FCHMOD system calls
* do_chown: perform the CHOWN and FCHOWN system calls
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* do_umask: perform the UMASK system call
* do_access: perform the ACCESS system call
* forbidden: check to see if a given access is allowed on a given inode
*/
#include "fs.h"
#include <unistd.h>
#include <minix/callnr.h>
#include "buf.h"
#include "file.h"
#include "fproc.h"
#include "inode.h"
#include "param.h"
#include "super.h"
/*===========================================================================*
* do_chmod *
*===========================================================================*/
PUBLIC int do_chmod()
{
/* Perform the chmod(name, mode) system call. */
register struct inode *rip;
register int r;
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if(call_nr == CHMOD) {
/* Temporarily open the file. */
if (fetch_name(m_in.name, m_in.name_length, M3) != OK) return(err_code);
if ( (rip = eat_path(user_path)) == NIL_INODE) return(err_code);
} else if(call_nr == FCHMOD) {
struct filp *filp;
if(!(filp = get_filp(m_in.m3_i1))) return(err_code);
rip = filp->filp_ino;
} else panic(__FILE__, "do_chmod called with strange call_nr", call_nr);
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/* 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 (rip->i_uid != fp->fp_effuid && !super_user)
r = EPERM;
else
r = read_only(rip);
/* If error, return inode. */
if (r != OK) {
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if(call_nr == CHMOD) put_inode(rip);
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return(r);
}
/* Now make the change. Clear setgid bit if file is not in caller's grp */
rip->i_mode = (rip->i_mode & ~ALL_MODES) | (m_in.mode & ALL_MODES);
if (!super_user && rip->i_gid != fp->fp_effgid)rip->i_mode &= ~I_SET_GID_BIT;
rip->i_update |= CTIME;
rip->i_dirt = DIRTY;
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if(call_nr == CHMOD) put_inode(rip);
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return(OK);
}
/*===========================================================================*
* do_chown *
*===========================================================================*/
PUBLIC int do_chown()
{
/* Perform the chown(name, owner, group) system call. */
register struct inode *rip;
register int r;
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if(call_nr == CHOWN) {
/* Temporarily open the file. */
if (fetch_name(m_in.name1, m_in.name1_length, M1) != OK) return(err_code);
if ( (rip = eat_path(user_path)) == NIL_INODE) return(err_code);
} else if(call_nr == FCHOWN) {
struct filp *filp;
if(!(filp = get_filp(m_in.m1_i1))) return(err_code);
rip = filp->filp_ino;
} else panic(__FILE__, "do_chown called with strange call_nr", call_nr);
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/* Not permitted to change the owner of a file on a read-only file sys. */
r = read_only(rip);
if (r == OK) {
/* FS is R/W. Whether call is allowed depends on ownership, etc. */
if (super_user) {
/* The super user can do anything. */
rip->i_uid = m_in.owner; /* others later */
} else {
/* Regular users can only change groups of their own files. */
if (rip->i_uid != fp->fp_effuid) r = EPERM;
if (rip->i_uid != m_in.owner) r = EPERM; /* no giving away */
if (fp->fp_effgid != m_in.group) r = EPERM;
}
}
if (r == OK) {
rip->i_gid = m_in.group;
rip->i_mode &= ~(I_SET_UID_BIT | I_SET_GID_BIT);
rip->i_update |= CTIME;
rip->i_dirt = DIRTY;
}
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if(call_nr == CHOWN) put_inode(rip);
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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. */
struct inode *rip;
register int r;
/* 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 whose access is to be checked. */
if (fetch_name(m_in.name, m_in.name_length, M3) != OK) return(err_code);
if ( (rip = eat_path(user_path)) == NIL_INODE) return(err_code);
/* Now check the permissions. */
r = forbidden(rip, (mode_t) m_in.mode);
put_inode(rip);
return(r);
}
/*===========================================================================*
* forbidden *
*===========================================================================*/
PUBLIC int forbidden(register struct inode *rip, mode_t access_desired)
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{
/* Given a pointer to an inode, 'rip', 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 struct inode *old_rip = rip;
register struct super_block *sp;
register mode_t bits, perm_bits;
int r, shift, test_uid, test_gid, type;
if (rip->i_mount == I_MOUNT) /* The inode is mounted on. */
for (sp = &super_block[1]; sp < &super_block[NR_SUPERS]; sp++)
if (sp->s_imount == rip) {
rip = get_inode(sp->s_dev, ROOT_INODE);
break;
} /* if */
/* Isolate the relevant rwx bits from the mode. */
bits = rip->i_mode;
test_uid = (call_nr == ACCESS ? fp->fp_realuid : fp->fp_effuid);
test_gid = (call_nr == ACCESS ? fp->fp_realgid : fp->fp_effgid);
if (test_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 (test_uid == rip->i_uid) shift = 6; /* owner */
else if (test_gid == rip->i_gid ) shift = 3; /* group */
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.
*/
type = rip->i_mode & I_TYPE;
if (r == OK)
if (access_desired & W_BIT)
r = read_only(rip);
if (rip != old_rip) put_inode(rip);
return(r);
}
/*===========================================================================*
* read_only *
*===========================================================================*/
PUBLIC int read_only(ip)
struct inode *ip; /* 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 super_block *sp;
sp = ip->i_sp;
return(sp->s_rd_only ? EROFS : OK);
}