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    SubjectRe: [PATCH] fs: Add flags to __d_path for suppressing suffix andmapping /proc/self
    Al Viro wrote:
    > > Also, procfs is usually mounted on /proc , but it can be mounted on /proc2 ,
    > > /mnt/proc3 or /p . Thus, the caller of __d_path() can't convert /proc/PID to
    > > /proc/self from string returned by __d_path() because the caller can't find
    > > the mount point of procfs from the returned string. If the caller traverses
    > > dentry/vfsmount tree in order to find the mount point of procfs, it results in
    > > duplicating __d_path() because the the caller does not use __d_path().
    > No. If you don't care which instance it is, you can bloody well check that
    > superblock is that of a procfs and track the path to its root *in* *caller*.

    I couldn't catch. Are you suggesting that TOMOYO should not call __d_path() for
    dentry if dentry->d_sb->s_magic == PROC_SUPER_MAGIC ?

    > Instead of calling d_path and looking at vfsmount tree at all. And you'd
    > better do that without assumptions that no name in procfs could be a number
    > unrelated to PIDs (i.e. you'd need to check that parent of your candidate
    > is root).

    I'm doing IS_ROOT(parent) to check that parent of dentry is root.

    > BTW, *any* filesystem may be mounted at several places at once. Moreover,
    > different subtrees of the same fs may be found at different mountpoints.

    Yes. I know.

    > IIRC,
    > back when "pathname-based" checks had been discussed, their proponents said
    > that they don't care if rules for different instances were inconsistent and
    > that it's OK to have them covered sepately, as long as you default to giving
    > lower permissions to unrecognized ones. Why is procfs an exception?

    Because procfs redirects /proc/self to /proc/PID using symlink when the
    userspace accesses information of current process. This redirection makes it
    impossible for name based checks to grant only accessing information of
    current process.

    What I want to do is to undo this redirection done by procfs. Undoing this
    redirection makes it possible for name based checks to grant only accessing
    information of current process.

    Granting /proc/self/ is more secure than granting /proc/*/ if userspace needs
    to access only information of current process.

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