posix_acl: Clear SGID bit when setting file permissions

When file permissions are modified via chmod(2) and the user is not in
the owning group or capable of CAP_FSETID, the setgid bit is cleared in
inode_change_ok().  Setting a POSIX ACL via setxattr(2) sets the file
permissions as well as the new ACL, but doesn't clear the setgid bit in
a similar way; this allows to bypass the check in chmod(2).  Fix that.

References: CVE-2016-7097
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Jan Kara <[email protected]>
Signed-off-by: Andreas Gruenbacher <[email protected]>
This commit is contained in:
Jan Kara 2016-09-19 17:39:09 +02:00
commit 073931017b
16 changed files with 89 additions and 102 deletions

View file

@ -78,13 +78,11 @@ static int __jfs_set_acl(tid_t tid, struct inode *inode, int type,
case ACL_TYPE_ACCESS:
ea_name = XATTR_NAME_POSIX_ACL_ACCESS;
if (acl) {
rc = posix_acl_equiv_mode(acl, &inode->i_mode);
if (rc < 0)
rc = posix_acl_update_mode(inode, &inode->i_mode, &acl);
if (rc)
return rc;
inode->i_ctime = CURRENT_TIME;
mark_inode_dirty(inode);
if (rc == 0)
acl = NULL;
}
break;
case ACL_TYPE_DEFAULT: