protect.c

一个简单的操作系统minix的核心代码

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				src/fs/protect.c	 	 
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26100	/* This file deals with protection in the file system.  It contains the code
26101	 * for four system calls that relate to protection.
26102	 *
26103	 * The entry points into this file are
26104	 *   do_chmod:  perform the CHMOD system call
26105	 *   do_chown:  perform the CHOWN system call
26106	 *   do_umask:  perform the UMASK system call
26107	 *   do_access: perform the ACCESS system call
26108	 *   forbidden: check to see if a given access is allowed on a given inode
26109	 */
26110	
26111	#include "fs.h"
26112	#include <unistd.h>
26113	#include <minix/callnr.h>
26114	#include "buf.h"
26115	#include "file.h"
26116	#include "fproc.h"
26117	#include "inode.h"
26118	#include "param.h"
26119	#include "super.h"
26120	
26121	/*===========================================================================*
26122	 *                              do_chmod                                     *
26123	 *===========================================================================*/
26124	PUBLIC int do_chmod()
26125	{
26126	/* Perform the chmod(name, mode) system call. */
26127	
26128	  register struct inode *rip;
26129	  register int r;
26130	
26131	  /* Temporarily open the file. */
26132	  if (fetch_name(name, name_length, M3) != OK) return(err_code);
26133	  if ( (rip = eat_path(user_path)) == NIL_INODE) return(err_code);
26134	
26135	  /* Only the owner or the super_user may change the mode of a file.
26136	   * No one may change the mode of a file on a read-only file system.
26137	   */
26138	  if (rip->i_uid != fp->fp_effuid && !super_user)
26139	        r = EPERM;
26140	  else
26141	        r = read_only(rip);
26142	
26143	  /* If error, return inode. */
26144	  if (r != OK)  {
26145	        put_inode(rip);
26146	        return(r);
26147	  }
26148	
26149	  /* Now make the change. Clear setgid bit if file is not in caller's grp */
26150	  rip->i_mode = (rip->i_mode & ~ALL_MODES) | (mode & ALL_MODES);
26151	  if (!super_user && rip->i_gid != fp->fp_effgid)rip->i_mode &= ~I_SET_GID_BIT;
26152	  rip->i_update |= CTIME;
26153	  rip->i_dirt = DIRTY;
26154	
26155	  put_inode(rip);
26156	  return(OK);
26157	}
	
	
26160	/*===========================================================================*
26161	 *                              do_chown                                     *
26162	 *===========================================================================*/
26163	PUBLIC int do_chown()
26164	{
26165	/* Perform the chown(name, owner, group) system call. */
26166	
26167	  register struct inode *rip;
26168	  register int r;
26169	
26170	  /* Temporarily open the file. */
26171	  if (fetch_name(name1, name1_length, M1) != OK) return(err_code);
26172	  if ( (rip = eat_path(user_path)) == NIL_INODE) return(err_code);
26173	
26174	  /* Not permitted to change the owner of a file on a read-only file sys. */
26175	  r = read_only(rip);
26176	  if (r == OK) {
26177	        /* FS is R/W.  Whether call is allowed depends on ownership, etc. */
26178	        if (super_user) {
26179	                /* The super user can do anything. */
26180	                rip->i_uid = owner;     /* others later */
26181	        } else {
26182	                /* Regular users can only change groups of their own files. */
26183	                if (rip->i_uid != fp->fp_effuid) r = EPERM;
26184	                if (rip->i_uid != owner) r = EPERM;     /* no giving away */
26185	                if (fp->fp_effgid != group) r = EPERM;
26186	        }
26187	  }
26188	  if (r == OK) {
26189	        rip->i_gid = group;
26190	        rip->i_mode &= ~(I_SET_UID_BIT | I_SET_GID_BIT);
26191	        rip->i_update |= CTIME;
26192	        rip->i_dirt = DIRTY;
26193	  }
26194	
26195	  put_inode(rip);
26196	  return(r);
26197	}
	
	
26200	/*===========================================================================*
26201	 *                              do_umask                                     *
26202	 *===========================================================================*/
26203	PUBLIC int do_umask()
26204	{
26205	/* Perform the umask(co_mode) system call. */
26206	  register mode_t r;
26207	
26208	  r = ~fp->fp_umask;            /* set 'r' to complement of old mask */
26209	  fp->fp_umask = ~(co_mode & RWX_MODES);
26210	  return(r);                    /* return complement of old mask */
26211	}
	
	
26214	/*===========================================================================*
26215	 *                              do_access                                    *
26216	 *===========================================================================*/
26217	PUBLIC int do_access()
26218	{
26219	/* Perform the access(name, mode) system call. */
26220	
26221	  struct inode *rip;
26222	  register int r;
26223	
26224	  /* First check to see if the mode is correct. */
26225	  if ( (mode & ~(R_OK | W_OK | X_OK)) != 0 && mode != F_OK)
26226	        return(EINVAL);
26227	
26228	  /* Temporarily open the file whose access is to be checked. */
26229	  if (fetch_name(name, name_length, M3) != OK) return(err_code);
26230	  if ( (rip = eat_path(user_path)) == NIL_INODE) return(err_code);
26231	
26232	  /* Now check the permissions. */
26233	  r = forbidden(rip, (mode_t) mode);
26234	  put_inode(rip);
26235	  return(r);
26236	}
	
	
26239	/*===========================================================================*
26240	 *                              forbidden                                    *
26241	 *===========================================================================*/
26242	PUBLIC int forbidden(rip, access_desired)
26243	register struct inode *rip;     /* pointer to inode to be checked */
26244	mode_t access_desired;  /* RWX bits */
26245	{
26246	/* Given a pointer to an inode, 'rip', and the access desired, determine
26247	 * if the access is allowed, and if not why not.  The routine looks up the
26248	 * caller's uid in the 'fproc' table.  If access is allowed, OK is returned
26249	 * if it is forbidden, EACCES is returned.
26250	 */
26251	
26252	  register struct inode *old_rip = rip;
26253	  register struct super_block *sp;
26254	  register mode_t bits, perm_bits;
26255	  int r, shift, test_uid, test_gid;
26256	
26257	  if (rip->i_mount == I_MOUNT)  /* The inode is mounted on. */
26258	        for (sp = &super_block[1]; sp < &super_block[NR_SUPERS]; sp++)
26259	                if (sp->s_imount == rip) {
26260	                        rip = get_inode(sp->s_dev, ROOT_INODE);
26261	                        break;
26262	                } /* if */
26263	
26264	  /* Isolate the relevant rwx bits from the mode. */
26265	  bits = rip->i_mode;
26266	  test_uid = (fs_call == ACCESS ? fp->fp_realuid : fp->fp_effuid);
26267	  test_gid = (fs_call == ACCESS ? fp->fp_realgid : fp->fp_effgid);
26268	  if (test_uid == SU_UID) {
26269	        /* Grant read and write permission.  Grant search permission for
26270	         * directories.  Grant execute permission (for non-directories) if
26271	         * and only if one of the 'X' bits is set.
26272	         */
26273	        if ( (bits & I_TYPE) == I_DIRECTORY ||
26274	             bits & ((X_BIT << 6) | (X_BIT << 3) | X_BIT))
26275	                perm_bits = R_BIT | W_BIT | X_BIT;
26276	        else
26277	                perm_bits = R_BIT | W_BIT;
26278	  } else {
26279	        if (test_uid == rip->i_uid) shift = 6;          /* owner */
26280	        else if (test_gid == rip->i_gid ) shift = 3;    /* group */
26281	        else shift = 0;                                 /* other */
26282	        perm_bits = (bits >> shift) & (R_BIT | W_BIT | X_BIT);
26283	  }
26284	
26285	  /* If access desired is not a subset of what is allowed, it is refused. */
26286	  r = OK;
26287	  if ((perm_bits | access_desired) != perm_bits) r = EACCES;
26288	
26289	  /* Check to see if someone is trying to write on a file system that is
26290	   * mounted read-only.
26291	   */
26292	  if (r == OK)
26293	        if (access_desired & W_BIT) r = read_only(rip);
26294	
26295	  if (rip != old_rip) put_inode(rip);
26296	
26297	  return(r);
26298	}
	
	
26301	/*===========================================================================*
26302	 *                              read_only                                    *
26303	 *===========================================================================*/
26304	PUBLIC int read_only(ip)
26305	struct inode *ip;               /* ptr to inode whose file sys is to be cked */
26306	{
26307	/* Check to see if the file system on which the inode 'ip' resides is mounted
26308	 * read only.  If so, return EROFS, else return OK.
26309	 */
26310	
26311	  register struct super_block *sp;
26312	
26313	  sp = ip->i_sp;
26314	  return(sp->s_rd_only ? EROFS : OK);
26315	}