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

@ -190,15 +190,11 @@ ext2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
case ACL_TYPE_ACCESS:
name_index = EXT2_XATTR_INDEX_POSIX_ACL_ACCESS;
if (acl) {
error = posix_acl_equiv_mode(acl, &inode->i_mode);
if (error < 0)
error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
if (error)
return error;
else {
inode->i_ctime = CURRENT_TIME_SEC;
mark_inode_dirty(inode);
if (error == 0)
acl = NULL;
}
inode->i_ctime = CURRENT_TIME_SEC;
mark_inode_dirty(inode);
}
break;