Re: Changes to the filesystem while find is running - comments?

From: James Youngman (bugtraq_at_excession.spiral-arm.org)
Date: 11/23/04

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    Date: Tue, 23 Nov 2004 00:00:41 +0000
To: Paul Szabo <psz@maths.usyd.edu.au>

    On Tue, Nov 23, 2004 at 07:39:56AM +1100, Paul Szabo wrote:

    > What I would like to see implemented (in some messy pseudo-code, starting
    > in parent directory):
    >
    > PARENT=stat(".");
    > SUBDIR=stat("subdir");
    > chdir("subdir");
    > DOT=stat(".");
    > if (SUBDIR != DOT) {
    > Print warning message /*[1]*/
    > }
    > else {
    > Go on with find (recurse)
    > }
    > chdir("..");
    > DOT=stat(".");
    > if (PARENT != DOT) {
    > Print message
    > Exit with fatal error
    > }
    >
    > Do not descend into "dodgy" directories, but back out of them; exit fatally
    > if you cannot get back to solid ground.
    >
    > Is this doable?

    Certainly. In fact it's how GNU findutils is implemented, except for
    the fact that the "warning message" is a fatal error in GNU findutils
    releases up to and including 4.2.5. In later versions (we're
    currently at 4.2.7 on ftp://alpha.gnu.org/gnu/findutils) a hack was
    introduced to try to support a special case which works when we've
    traversed an automount mount point on Solaris).

    This algorithm is certainly robust, but it will never descend into an
    automount directory hierarchy. Do you think we can do better than
    that without opening the door to more exploits?

    Regards,
    James.

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