Re: [PATCH -mm 5/7] add user namespace

Eric W. Biederman
2006-07-14T17:37:38Z

Dave Hansen <haveblue@us.ibm.com> writes:

> On Fri, 2006-07-14 at 12:08 -0500, Serge E. Hallyn wrote:
>> yes, of course, vfsmount, which I assume is what Eric meant?
>>
>> Which means we'd have to do this at permission() using the nameidata, or
>> pass nd to generic_permission.
>
> Yeah, I think so. But, this is well into Al territory, and there might
> be a better way.

Well until we get that sorted out I will keep picking on i_sb.

The one thing that just occurred to me is that the generic permission
should end up structured as below. I don't know if it is cheaper
but it is certainly more obvious.

Eric

int generic_permission(struct inode *inode, int mask,
int (*check_acl)(struct inode *inode, int mask))
{
umode_t mode = inode->i_mode;

+ if (unlikely(current->nsproxy->user_ns != inode->i_sb->user_ns))
+ goto unknown_user;

if (current->fsuid == inode->i_uid)
mode >>= 6;
else {
if (IS_POSIXACL(inode) && (mode & S_IRWXG) && check_acl) {
int error = check_acl(inode, mask);
if (error == -EACCES)
goto check_capabilities;
else if (error != -EAGAIN)
return error;
}

if (in_group_p(inode->i_gid))
mode >>= 3;
}
+ unknown_user:

/*
* If the DACs are ok we don't need any capability check.
*/
if (((mode & mask & (MAY_READ|MAY_WRITE|MAY_EXEC)) == mask))
return 0;

check_capabilities:
/*
* Read/write DACs are always overridable.
* Executable DACs are overridable if at least one exec bit is set.
*/
if (!(mask & MAY_EXEC) ||
(inode->i_mode & S_IXUGO) || S_ISDIR(inode->i_mode))
if (capable(CAP_DAC_OVERRIDE))
return 0;

/*
* Searching includes executable on directories, else just read.
*/
if (mask == MAY_READ || (S_ISDIR(inode->i_mode) && !(mask & MAY_WRITE)))
if (capable(CAP_DAC_READ_SEARCH))
return 0;

return -EACCES;
}