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    SubjectRe: [PATCH 2/3] fs/binfmts: Better handling of binfmt loops
    On Tue, 30 Jul 2013 16:16:51 -0700 Zach Levis <zml@linux.vnet.ibm.com> wrote:

    >
    > Quoting Andrew Morton <akpm@linux-foundation.org>:
    >
    > > On Thu, 25 Jul 2013 08:40:44 -0700 Zach Levis <zml@linux.vnet.ibm.com> wrote:
    > >
    > >> With these changes, when a binfmt loop is encountered,
    > >> the ELOOP will propogate back to the 0 depth. At this point the
    > >> argv and argc values will be reset to what they were originally and an
    > >> attempt is made to continue with the following binfmt handlers.
    > >
    > > hm, why? What problem does this fix? What value does the change offer
    > > to our users?
    >
    > This is used when the binfmt_misc,script,etc options are configured in
    > a way that would previously prevent executables from launching that
    > could be executed with a different binfmt but don't because of a loop
    > in a prior binfmt.
    >
    > Example: a qemu is configured to run 64-bit ELFs on an otherwise
    > 32-bit system. The system's owner switches to running with 64-bit
    > executables, but forgets to disable the binfmt_misc option that
    > redirects 64bit ELFs to qemu. Since the qemu executable is a 64-bit
    > ELF now, binfmt_misc keeps on matching it with the qemu rule,
    > preventing the execution of any 64-bit binary.

    So the admin can unforget to make that change and no longer has a problem.

    > With this patch, an error is printed and search_binary_handler()
    > continues on to the next handler, allowing the original executable to
    > run normally so the user can (hopefully) fix their misconfiguration
    > more easily.

    Is all this really worth changing the kernel for? It sounds
    a bit marginal.


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