This is the command scanmem that can be run in the OnWorks free hosting provider using one of our multiple free online workstations such as Ubuntu Online, Fedora Online, Windows online emulator or MAC OS online emulator
PROGRAM:
NAME
scanmem - locate and modify a variable in an executing process.
SYNOPSIS
scanmem [--version] [--help] [--debug] [--backend] target-program-pid
DESCRIPTION
scanmem is an interactive debugging utility that can be used to isolate the address of a
variable in an executing process by successively scanning the process' address space
looking for matching values. By informing scanmem how the value of the variable changes
over time, it can determine the actual location (or locations) of the variable by
successively eliminating non-matches. scanmem determines where to look by searching for
mappings with read / write permission, these are referred to as regions. Users can
eliminate regions they believe are likely unrelated to the target variable (for example,
located in a shared library unrelated to the variable in question), this will improve the
speed of the scan, which can initially be quite slow in large programs.
Once a variable has been found, scanmem can monitor the variable, or change it to a user
specified value, either once, or continually over a period of time.
scanmem works similarly to the " pokefinders " once commonly used to cheat at video games,
this function is a good demonstration of how to use scanmem , and is used in the
documentation.
USAGE
scanmem should be invoked with the process id of the program you wish to debug as an
argument. Once started, scanmem accepts interactive commands. These are described below,
however entering help at the > prompt will allow you to access scanmem's online
documentation.
The target-program-pid can be specified in decimal, hexadecimal, or octal using the
standard C language notation (leading 0x for hexadecimal, leading 0 for octal, anything
else is assumed to be decimal).
--version
Print version and exit.
--help
Print a short description of command line options then exit.
--debug
Run in debug mode, more information will be outputted.
--backend
Work as backend, normal users should not use this paratmeter.
COMMANDS
While in interactive mode, scanmem prints a decimal number followed by > , the number is
the current number of possible candidates for the target variable that are known. 0
indicates that no possible variables have been eliminated yet.
n
Where n represents any number in decimal, octal or hexadecimal, this command tells scanmem
that the current value of the target variable is exactly n. scanmem will begin a search
of the entire address space, or the existsing known matches (if any), eliminating any
variable that does not have this value.
set [match-id][,match-id,...]=]value[/delay] [...]
Set the value value into the match numbers match-id , or if just value is specified, all
known matches. value can be specified in standard C language notation. All known matches,
along with their match-id's can be displayed using the list command. Multiple match-id's
can be specified, separated with commas and terminated with an = sign. To set a value
continually, suffix the command with / followed by the number of seconds to wait between
sets. You can interrupt the set command with ^C to return to the scanmem prompt. This can
be used to sustain the value of a variable which decreases overtime, for example a timer
that is decremented every second can be set to 100 every 10 seconds to prevent some
property from ever changing.
This command is used to change the value of the variable(s) once found by elimination.
Please note, some applications will store values in multiple locations.
dump <address> <length> [<filename>]
Dump the memory region starting from <address> of length <length> into a human-readable
format.
If <filename> is given, data will be saved into the file, otherwise data will be displayed
into stdout in a human readable format
write <value_type> <address> <value>
Manually set the value of the variable at the speicified address.
Names of value_type are subject to change in different versions of scanmem, see more info
using the `help write' command.
>
Tells scanmem that it should eliminate all matched variables that have not increased since
the last search. For example, if the value of a variable is known to be zero when a
program is executed, but increases over time, this command can be used several times to
eliminate variables that have decreased or not changed.
<
As for > but indicates that the target variable has decreased since the last scan.
=
As for > but indicates that the target variable has not changed since last scan.
snapshot
Save a snapshot of existing program state, for use with > , < , and = , although other
commands can still be used.
list
List all the possible candidates currently known, including their address, last known
value and possible types. The value in the first column is the match id, and can be used
in conjunction with the delete command to eliminate matches.
delete [match-id]
Delete match match-id , which can be found from the output of the list command. To delete
all matches, see the reset command, or to delete all matches associated with a particular
library, see the dregion command, which also removes any associated matches. Pleae note
that match-ids may be recalculated after matches are removed or added.
watch [match-id]
Monitor the value of match-id , and print its value as it changes. Every change is printed
along with a timestamp, you can interrupt this command with ^C to stop monitoring.
pid [new-pid]
Print out the process id of the current target program, or change the target to new-pid ,
which will reset existing regions and matches.
lregions
List all the known regions, this can be used in combination with the dregion command to
eliminate regions that the user believes are not related to the variable in question, thus
reducing the address space required to search. The value in the first column is the
region-id which must be passed to the dregion command. The size and path (if applicable)
is also printed. This can be used to eliminate regions located in shared libraries that
are unlikely to be relevant to the variable required.
dregion [!][region-id][,region-id][,...]
Delete the region region-id , along with any matches from the match list. The region-id
can be found in the output of the lregions command. A leading ! indicates the list should
be inverted.
reset
Forget all known matches and start again.
shell [shell-command]
Execute shell-command using /bin/sh, then return.
option <name> <value>
Change options in runtime. See `help option` for all possible names/values.
version
Print the version of scanmem in use.
help
Print a short summary of available commands.
exit
Detach from the target program and exit immediately.
EXAMPLES
Cheat at nethack, on systems where nethack is not installed sgid.
$ scanmem `pidof nethack`
info: attaching to pid 13070.
info: maps file located at /proc/13070/maps opened.
info: 17 suitable regions found.
Please enter current value, or "help" for other commands.
0>
The 0 in the scanmem prompt indicates we currently have no candidates, so I enter how much
gold I currently have (91 pieces) and let scanmem find the potential candidates.
0> 91
info: searching 0xbfffa000 - 0xc0000000...........ok
info: searching 0x401c2000 - 0x401e3000...........ok
info: searching 0x401c1000 - 0x401c2000...........ok
info: searching 0x401b6000 - 0x401b8000...........ok
info: searching 0x401b5000 - 0x401b6000...........ok
info: searching 0x40189000 - 0x4018a000...........ok
info: searching 0x40188000 - 0x40189000...........ok
info: searching 0x40181000 - 0x40183000...........ok
info: searching 0x4017f000 - 0x40181000...........ok
info: searching 0x40070000 - 0x40071000...........ok
info: searching 0x40068000 - 0x40070000...........ok
info: searching 0x40030000 - 0x40031000...........ok
info: searching 0x40029000 - 0x4002a000...........ok
info: searching 0x4001f000 - 0x40020000...........ok
info: searching 0x40016000 - 0x40017000...........ok
info: searching 0x081d4000 - 0x0820a000...........ok
info: searching 0x081b7000 - 0x081d4000...........ok
info: we currently have 16 matches.
16> list
[ 0] 0x081c1f34 { 91} (/usr/share/games/nethack/nethack)
[ 1] 0x081c1780 { 91} (/usr/share/games/nethack/nethack)
[ 2] 0x081be436 { 91} (/usr/share/games/nethack/nethack)
[ 3] 0x081eeffc { 91} (unassociated, typically .bss)
[ 4] 0x081ee0c0 { 91} (unassociated, typically .bss)
[ 5] 0x081eddb8 { 91} (unassociated, typically .bss)
[ 6] 0x081d6d88 { 91} (unassociated, typically .bss)
[ 7] 0x4001fcd3 { 91} (/lib/libnss_compat-2.3.5.so)
[ 8] 0x40029fe3 { 91} (/lib/libnss_nis-2.3.5.so)
[ 9] 0x40029f8b { 91} (/lib/libnss_nis-2.3.5.so)
[10] 0x40029efb { 91} (/lib/libnss_nis-2.3.5.so)
[11] 0x40029bff { 91} (/lib/libnss_nis-2.3.5.so)
[12] 0x401d18d3 { 91} (unassociated, typically .bss)
[13] 0x401d156f { 91} (unassociated, typically .bss)
[14] 0x401d120b { 91} (unassociated, typically .bss)
[15] 0xbfffd76c { 91} (unassociated, typically .bss)
16>
16 potential matches were found, many of them are clearly unrelated, as they're part of
unrelated libraries (libnss_nis.so). We could make scanmem eliminate these manually using
the delete command, however just waiting until the amount of gold changes and telling
scanmem the new value should be enough. I find some more gold, and tell scanmem the new
value, 112.
16> 112
info: we currently have 1 matches.
info: match identified, use "set" to modify value.
info: enter "help" for other commands.
1> list
[ 0] 0x081d6d88 { 112} (unassociated, typically .bss)
Only one of the 16 original candidates now have the value 112, so this must be where the
amount of gold is stored. I'll try setting it to 10,000 pieces.
1> set 10000
info: setting *0x081d6d88 to 10000...
1>
The resulting nethack status:
Dlvl:1 $:10000 HP:15(15) Pw:2(2) AC:7 Exp:1
NOTES
scanmem has been tested on multiple large programs, including the 3d shoot-em-up quake3
linux.
Obviously, scanmem can crash your program if used incorrectly.
Some programs store values in multiple locations, this is why set will change all known
matches.
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