code:access - ikarishinjieva/unixV6-code-analyze-chs GitHub Wiki

6730

6731 /*

6732  * Check mode permission on inode pointer.

6733  * Mode is READ, WRITE, or EXEC.

6734  * In the case of WRITE, the

6735  * read-only status of the file

6736  * system is checked.

6737  * Also in WRITE, prototype text

6738  * segments cannot be written.

6739  * The mode is shifted to select

6740  * the owner/group/other fields.

6741  * The super user is granted all

6742  * permissions except for EXEC where

6743  * at least one of the EXEC bits must

6744  * be on.

6745  */

6746 access(aip, mode)

6747 int *aip;

6748 {

• IWRITE,IEXEC,IREAD 权限常量定义在inode.h

6749     register *ip, m;

6750

6751     ip = aip;

6752     m = mode;

6753     if(m == IWRITE) {

6754          if(getfs(ip->i_dev)->s_ronly != 0) {

6755           u.u_error = EROFS;

6756           return(1);

6757          }

• 若尝试写 只读的文件系统，则抛出EROFS

6758          if(ip->i_flag & ITEXT) {

6759           u.u_error = ETXTBSY;

6760           return(1);

6761          }

• 若尝试写 作为程序正文的文件，则抛出ETXTBSY

6762     }

6763     if(u.u_uid == 0) {

6764          if(m == IEXEC && (ip->i_mode &

6765                     (IEXEC | (IEXEC>>3) | (IEXEC>>6))) == 0)

6766           goto bad;

6767          return(0);

6768     }

• 当前用户为超级用户
  • 若尝试执行无执行权限的文件，则抛出EACCES
  • 其他情况，超级用户拥有完全权限

6769     if(u.u_uid != ip->i_uid) {

6770          m =>> 3;

6771          if(u.u_gid != ip->i_gid)

6772           m =>> 3;

6773     }

6774     if((ip->i_mode&m) != 0)

6775          return(0);

• 若 当前用户 为 文件拥有者，则 文件权限 对比 拥有者权限
  • 否则，若 当前用户 属于 文件拥有组，则 文件权限 对比 拥有组权限
    • 否则，文件权限 对比 其他用户权限
• 若验证通过，则返回0，否则抛出EACCES

6776

6777 bad:

6778     u.u_error = EACCES;

6779     return(1);

6780 }

6781 /* ------------------------- */

• 文件系统#文件权限

• code:exec
• code:chdir
• code:core
• code:open1
• code:namei