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    SubjectRe: modprobe problem with block-major-11
    On Thu, 25 Oct 2001 00:52:03 -0700, 
    Mike Castle <> wrote:
    >alias block-major-11 sr_mod # load sr_mod upon access of scd0
    >pre-install sr_mod modprobe ide-scsi # load ide-scsi before sr_mod

    * User does 'head /dev/scd0'.
    * The kernel runs modprobe block-major-11. modprobe is running
    setuid(0) because the original user was not root.
    * modprobe maps block-major-11 to sr_mod.
    * modprobe sees a pre-install command for sr_mod and uses system() to
    invoke the command.
    * The system() function issues '/bin/sh -c "command"', sh is linked to
    * Bash detects that it was invoked as 'sh' and is running setuid. Bash
    silently turns off the setuid privilege before running the command.
    * The second command (modprobe ide-scsi) needs root authority but bash
    has removed the authority. modprobe fails :(

    The problem is caused by a bash "feature", it was added in bash 2.01.
    I cannot fix it without writing my own replacement for the system()
    function. Doing setuid(0) in modprobe before calling system() would
    reopen the security exposure that was closed in modutils 2.3.21, that
    is not an option.

    Workaround: Replace
    pre-install foo modprobe bar
    before foo bar
    That does all the work internally without using the system() function
    and falling foul of the bash feature. It is also faster and it lets
    modprobe maintain the chain of modules for unload.

    BTW, users can never run rmmod, only root can do that.

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