MNT_NOEXEC on root filesystem with diskless PXE boot?

From: Tom Alsberg (alsbergt_at_zoopee.org)
Date: 03/31/05

  • Next message: Christoph Hellwig: "Re: So, who makes this one run FreeBSD? ;-)" 
    Date: Thu, 31 Mar 2005 13:16:25 +0200
To: FreeBSD Hackers List <freebsd-hackers@freebsd.org>

    Perhaps this should go to -STABLE, I just couldn't be sure.

    We are trying out FreeBSD 5.4-PRERELEASE on diskless clients. I
    noticed one problem, being that when setting the LD_LIBRARY_PATH
    (or for that matter, LD_PRELOAD, and LD_LIBMAP_DISABLE) environment
    variables, nothing will run, as /libexec/ld-elf.so.1 complains:

    Cannot execute objects on /

    According to the sources, this was added in 5.4, and will happen
    if / is mounted noexec.

    In this case, / is mounted by the BTX PXE loader over NFS (from a
    FreeBSD 5.3 server, right now). "mount" does not show the noexec
    flag. However, with the attached little C program I verified that
    statfs really returns this flag (0x00000006).

    Now, I see that on FreeBSD 5.3 diskless clients this flag is also
    returned on / - just it happened that nobody looked at it until
    the change in rtld.c of FreeBSD 5.4:

    if (fs.f_flags & MNT_NOEXEC) {
            _rtld_error("Cannot execute objects on %s\n", fs.f_mntonname);
            close(fd);
            return NULL;
    }

    I didn't yet understand (didn't check much) - why does statfs report
    the MNT_NOEXEC flag on the / filesystem (and only the / filesystem,
    when it's mounted from NFS by the bootloader - not any other
    NFS filesystems)? BTW, this happens also with NetApp as the NFS
    server - just to rule out any possibility of relation here.

      Ideas appreciated,
      -- Tom 

    -- 
  Tom Alsberg - certified insane, complete illiterate.
	Homepage: http://www.cs.huji.ac.il/~alsbergt/
  * An idea is not responsible for the people who believe in it.

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