The ELF Virus Writing HOWTO: sparc-sunos5.7
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# 7. Scanners

| Enough research will tend to support your theory.
| Murphy's Law of Research

This is the platform dependent part of Scanners (i). It contains three things:

- Verifying peculiarities of system files.

- Choosing appropriate targets to demonstrate infection methods.

- Testing scanners on all infected executables.

All together this results in a kind of time warp. The infection methods detected here are described later on.

## 7.1. Finding executables

First a sample from `file` to show how the `sed` part is supposed to work.

Source: pre/sparc-sunos5.7/scanner/file.sh

    #!/usr/xpg4/bin/sh
    /usr/bin/file /usr/xpg4/bin/sh | /usr/bin/fmt

Output: out/sparc-sunos5.7/scanner/file

    /usr/xpg4/bin/sh:       ELF 32-bit MSB executable SPARC Version 1,
    dynamically linked, stripped

And now the output of `find_exec.sh` for both the big and the small set of target executables. Linux distributions and Solaris have very few statically linked programs. On FreeBSD the number is much higher.

Output: out/sparc-sunos5.7/scanner/big.wc

    [] /bin /sbin /usr/bin /usr/sbin /usr/lib
          10 out/sparc-sunos5.7/scanner/big.static
         729 out/sparc-sunos5.7/scanner/big.dynamic
         739 total

Output: out/sparc-sunos5.7/scanner/small.wc

    [_infected] tmp/sparc-sunos5.7
           0 out/sparc-sunos5.7/scanner/small.static
           5 out/sparc-sunos5.7/scanner/small.dynamic
           5 total

## 7.2. Scan entry point

See Sections for the illustrative description of a dumped ELF header.

Output: out/sparc-sunos5.7/scanner/entry_point/big.static

    files=0010; detected=0000

Output: out/sparc-sunos5.7/scanner/entry_point/big.dynamic

    files=0729; detected=0000

Well, on a clean system there are absolutely no deviations. Now we let the script loose on all infected executables produced from the sources of this document. Only a few are detected (note the directory name `e1i1`). Which means there is cure against this vulnerability (see The entry point). In the following output `ep` means "entry point" and `sot` is "start of .text".

Output: out/sparc-sunos5.7/scanner/entry_point/small.dynamic

    segment_padding/e1i1/csh_infected            ep=0x32da0    sot=0x18a14
    segment_padding/e1i1/perl_infected           ep=0xf74c0    sot=0x24440
    segment_padding/e1i1/mt_infected             ep=0x117a0    sot=0x10a90
    segment_padding/e1i1/sh_infected             ep=0x3e510    sot=0x175c4
    segment_padding/e1i1/strip_sh_infected       ep=0x3e510    sot=0x175c4
    files=0005; detected=0005

## 7.3. Scan segments

Note that only the last few lines of output are shown.

Output: out/sparc-sunos5.7/scanner/segment/big.static

    files=10; ok=10; det_page=0; det_align=0; min=0x10001; max=0x10002

Output: out/sparc-sunos5.7/scanner/segment/big.dynamic

    CHECK: 65536 > 65536; 0x10000 > 0x10000
    CHECK: /usr/lib/svr4.make
    CHECK: src/scanner/segment/action.inc#17
    CHECK: (delta) > (0x10000)
    CHECK: 65536 > 65536; 0x10000 > 0x10000
    CHECK: /usr/lib/smrsh
    CHECK: src/scanner/segment/action.inc#17
    CHECK: (delta) > (0x10000)
    CHECK: 65536 > 65536; 0x10000 > 0x10000
    files=729; ok=729; det_page=0; det_align=269; min=0x10000; max=0x10002

On this installation at least 729 + 10 files are possible targets for Segment padding infection. So on to all infected executables created from the sources of this document. Again only the last few lines of output is shown. It's enough to see that all infected files are detected.

Output: out/sparc-sunos5.7/scanner/segment/small.dynamic

    CHECK: 61440 > 65536; 0xf000 > 0x10000
    CHECK: tmp/sparc-sunos5.7/segment_padding/e1i1/sh_infected
    CHECK: src/scanner/segment/action.inc#17
    CHECK: (delta) > (0x10000)
    CHECK: 61442 > 65536; 0xf002 > 0x10000
    CHECK: tmp/sparc-sunos5.7/segment_padding/e1i1/strip_sh_infected
    CHECK: src/scanner/segment/action.inc#17
    CHECK: (delta) > (0x10000)
    CHECK: 61442 > 65536; 0xf002 > 0x10000
    files=5; ok=5; det_page=0; det_align=5; min=0xf000; max=0xf002

## 7.4. A shell for segment padding

I want to demonstrate infection methods on a shell. The usual suspect is `/bin/sh`. But on some systems that particular executable is not vulnerable to Segment padding infection.

Source: pre/sparc-sunos5.7/scanner/find-shell.sh

    #!/usr/xpg4/bin/sh
    /usr/xpg4/bin/sed -ne 's/ \.\.\. .* Ok$//p' \
    	out/sparc-sunos5.7/scanner/segment/big.dynamic.full \
    	out/sparc-sunos5.7/scanner/segment/big.static.full \
    | /usr/xpg4/bin/grep -f ./src/scanner/find-shell.lst
    /usr/bin/echo status=$?

Source: src/scanner/find-shell.lst

    bin/ash\>
    bin/bash\>
    bin/bsh\>
    bin/csh\>
    bin/ksh\>
    bin/sash\>
    bin/sh\>
    bin/tcsh\>

Output: out/sparc-sunos5.7/scanner/find-shell

    /usr/bin/csh
    /usr/bin/ksh
    /usr/bin/sh
    /sbin/sh
    status=0

## 7.5. Scan file size

Output: out/sparc-sunos5.7/scanner/filesize/big.dynamic

    files=729; ok=729; detected=0

Output: out/sparc-sunos5.7/scanner/filesize/big.static

    files=10; ok=10; detected=0

Output: out/sparc-sunos5.7/scanner/filesize/small.dynamic

    files=5; ok=5; detected=0

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