fs/exec.c and binfmt-xxx in 2.4.14

[Heinz-Ado Arnolds <Ado.Arnolds@dhm-systems.de>]

Hi Linus, Hi Alan, Hi all,

I have a problem with loading modules for binary formats. The
reason for this problem shows up in fs/exec.c search_binary_handler().

Starting with linux-2.1.23 (and up to 2.4.14) there was a change
in the format and offset of printing the magic number for requesting
a handler module. Up to 2.1.22 the statement

    sprintf(modname, "binfmt-%hd", *(unsigned short *)(&bprm->buf[0]));
                              ^^                                 ^^^

was used. Now, and up to 2.4.14, the statement is:

    sprintf(modname, "binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
                              ^^^                                 ^^^

This leads to a request for loading a module which doesn't exist.
Additionally the request is now done with a hex number but modprobe
expects decimal numbers.

>From modutils-2.4.12/util/alias.h:

    ...
    "binfmt-267 binfmt_aout",
    ...
    "binfmt-332 iBCS",
    ...

When i now try to start an older binary in a.out format, which has a
magic number of 0x010b0064, it is translated with the 'new' code to a
request for "binfmt-0064" instead of "binfmt-267" as expected and
properly handled by modprobe.

Another example: for an old COFF executable with magic number
0x014c0004 the generated request is "binfmt-0004" instead of the
correct value "binfmt-332".

Wouldn't it be appropriate to revert the changes to format "%hd"
and use buffer offset 0 again?

Thanks a lot for your help and many greetings from Cologne, Germany

Ado

-- 
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  Heinz-Ado Arnolds                        Ado.Arnolds@web-systems.net
  Websystems GmbH                              +49 2234 1840-0 (voice)
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