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    SubjectRe: [PATCH -mm 5/7] add user namespace
    Date
    "Serge E. Hallyn" <serue@us.ibm.com> writes:

    > Quoting Eric W. Biederman (ebiederm@xmission.com):
    >> Dave Hansen <haveblue@us.ibm.com> writes:
    >>
    >> > On Thu, 2006-07-13 at 21:45 -0600, Eric W. Biederman wrote:
    >> >> I think for filesystems like /proc and /sys that there will normally
    >> >> be problems. However many of those problems can be rationalized away
    >> >> as a reasonable optimization, or are not immediately apparent.
    >> >
    >> > Could you talk about some of these problems?
    >>
    >> Already mentioned but. rw permissions on sensitive files are for
    >> uid == 0. No capability checks are performed.
    >
    > As Herbert (IIRC) pointed out that could/should be fixed.

    Capabilities have always fitted badly in with the normal unix
    permissions. So if we have a solution that works nicely with normal
    unix permissions we will have a nice general solution, that is
    easy for people to understand.

    What I am talking about is making a small tweak to the permission
    checking as below. Why do you keep avoiding even considering it?

    Eric

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

    - if (current->fsuid == inode->i_uid)
    + if ((current->fsuid == inode->i_uid) &&
    + (current->nsproxy->user_ns == inode->i_sb->user_ns))
    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))
    + if (in_group_p(inode->i_sb->user_ns, inode->i_gid))
    mode >>= 3;
    }

    /*
    * 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;
    }

    -
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