find Command as Admin Security Tool

Transcription

1 find Command as Admin Security Tool Dr. Bill Mihajlovic INCS-620 Operating Systems Security find Command find command searches for the file or files that meet certain condition. like: Certain name Certain size Certain access permissions Not or Yes accessed for n days Has m links Is owned by some user, or does not have owner, Flexible logic search expressions, etc. 1

2 find Command find command searches for the files only in the directories for which the user has access permission: Certain name find Example find is very powerful but hard to use file management command. # find /dirx name filex -print Search starts at /dirx Criterion is FileName = filex Each time found printing of the pathname is done The expression print says display the path names of all matching files. The expression name filename returns true for those files matching filename. 2

3 find Example -name To find filey anywhere under /dirx by name, use: # find /dirx name filey print To find all c-language source files, use: # find /dirx name *.c -print To find all files that end with one letter extenssion, use: # find /dirx name *.? -print find Example -atime To find all files under /dirx that have been accessed exactly 7 days ago, use: # find /dirx atime 7 -print To find all files under /dirx that have been accessed 14 days ago or later (in less than 14 days ago), use: # find /dirx atime -14 -print 3

4 find Example mtime To find all files last modified exactly 20 days ago, use: # find /dirx mtime 20 -print To find all files that have been modified in more than 40 days ago, use: # find /dirx mtime +40 -print To find all files last modified in less than 20 days ago, use: # find /dirx mtime -20 -print find Example core To find all core files older than 7 days and remove them form the system, use: # find / name core -mtime -7 \ -exec rm {} \; Core files are entire memory map snap-shot memory- content copy files made at a time of OS kernel crush. In case of intrusion caused system crush, core dump file analysis may help perform forensic analysis. Core files are huge on powerful memory rich servers! Must be periodically removed. 4

5 find Groups of Files Print all files under /usr/src ending in.c or.p: # find /usr/src name *.[cp] -print exec Example Remove (-exec rm {}) all ordinary files ( type f) of fewer than 30 characters (-size 30c) under the directory /dirz: # find /dirz type f -size 30c \ -exec rm {} \; 5

6 find Example Relative Age Produce a list of names of all files under the directory /var modified d since /etc/logfie was modified: d # find /var newer /etc/logfile -print find Example Illegal Words Find and print every line of every file on the system that contains the text string sex (or maybe d drugs ). # find / exec grep sex {} \; 6

7 Finding Files Links via Common ID Numbers Linked files are identical to the original and may be located in many directories under various names, (all linked files must have the same i-node number) To locate all links to a file one must first get the i-node of a one of the linked files and than search for all linked files. To find all links to vi program do the following: # ls li vi rwxr-xr-x Mar 1 vi # find / -inum print /usr/bin/vi /usr/bin/edit /usr/bin/ex /usr/bin/view /usr/bin/vedit # Finding Files Without Owner Every file on a Unix system will have an owner and an associated UID. Numeric user identifier with a normal long listing, instead of the name mean that the identifier doesn't correspond to any currently defined user or, at least, that the owner's entry has been removed from the /etc/passwd file or NIS/NIS+ map. To locate files that are not associated with any currently defined user, you can look for numeric identifiers in long listings or search for them by using the find criteria "-nouser"" as shown in this example: # find./* -nouser -ls -rwxr-xr-x Mar 11 /export/home/bud/filex 7

8 Find Files with no User To locate files that are not associated with any currently defined user, you can look for numeric identifiers in long listings or search for them by using the find criteria -nouser" as shown in this example: # find./* -nouser -ls -rwxr-xr-x Mar 1 /export/home/bud/datafile -rw-r-xr Mar 7 /export/home/bud/filex # Find Given User s Files To locate files that belong to certain user (e.g. frank) or associated group (e.g. students), in a mixture of many files belonging to many users, one can use user and group option with an OR o operator: # find./ \( -user frank o group students \) -print /export/home/frank/project.c /export/home/frank/.profile /export/home/jo/fx # To prevent the shell from interpreting itself, the escape character \ is necessary with characters ( and ). 8

9 find Example It is necessary to quote any file arguments that contain *,?. or [. # find. name poem.? -print Logical Tests and Search One can ad any number of tests yo yhe find-test list. Each test in a sequence is ANDed so the final action is invoked only if all the tests return TRUE. No explicit AND operator is needed; simply use spaces between tests. # find. name poem.? -size +2 -perm 711 -print This lists only files matching poem.?, that have more than 2 blocks of storage and has permissions rwx- x--x 9

10 Logical Tests Tests can be logically ORed using the o operator, or logically reversed with the! (bang) operator. The three logical operators, OR (-o), AND (implied by space), and NOT (!), can be combined in any way required. Logical operator precedence must be observed. (higher precedence operators must be applied before the lower precedence operators.) To override precedence or to enhance legibility, use the escaped parentheses \( and \). # find./ \( name poem.? or name poet* \) -size +2 -print \(, \) Escaped Parentheses If you do use un escaped parentheses with find, the shell will try to interpret Boolean expressions commands. Boolean expression should be evaluated by the find command not by the shell. Escape \ character neutralizes default shell-meaning of the following character, (Performs an escape from the default-common reality-meaning i of the escapedcharacter. 10

11 -size Arguments Argument Meaning n TRUE if file has exactly n blocks +n TRUE if file has more than n blocks -n TRUE if file has less than n blocks find Example? Print all files owned by root with permission rws x x or rwsr-xr-x: # find / user root perm print 11

12 find Command Expressions Expression -name filename -size [+ -]n Definition Finds files matching the specified filename. Metacharacters are acceptable if placed inside quotes. Finds files that are larger than +n, smaller than n, or exactly n. The n represents 512-byte blocks. -atime [+ -]n Finds files that have been accessed more than +n, less than -n, or exactly n days. -mtime [+ -]n Finds files that have been modified d more than +n, less than -n, or exactly n days. -user loginid Finds all files that are owned by the login IDname. -type Finds a file type; for example, f (file) or d (directory). -perm Finds files that have certain access permission bits. find Command Actions Action -exec command {} \; -ok command {} \; -print -ls Definition Executes the specified command on each file located, automatically. A set of braces, {}, delimits where the file name is passed to the command from the preceding expressions. A space, backslash, and semicolon, \;, delimits the end of the command. There must be a space before the backslash ( \). Interactive form of -exec. It requires input before find applies the command to the file; otherwise, it behaves as the -exec action. Instructs find to print the current path name to the terminal screen. This is the default. Prints the current path name, together with its associated statistics, such as inode number, size in kilobytes, protection mode, number of hard links, and user. 12

13 Find Disk Abusers Find out who the top ten users of disc space are on your system. #!/bin/sh # spacehogs find / -type f -exec /bin/ls -ls {} ';' awk ' { using[$4] += $1 } END { for (name in using) { print using[name], name } }' sort -nr head exit 0 SETUID/SETGID Programs Find all the SETUID/SETGID programs on your system: #!/bin/sh # find -setuid SUIDFILES=/etc/sfiles TEMPFILE=/tmp/$0.$$ find / -type f -a \( -perm o -perm 4000 \) -print > $TEMPFILE if [! -f $SUIDFILES ]; then echo "$0: creating list of SUID/SGID files in $SUIDFILES" mv $TEMPFILE $SUIDFILES chmod 400 $SUIDFILES else echo "$0: differences between current and past SUID/SGID files:" diff $TEMPFILE $SUIDFILES fi 13

14 Find Large FIles Find the top ten files (by size) on your system and who owns them: #!/bin/sh # top-ten-files if [ "$1" = "" ]; then WHERE=/ else #WHERE="$1 -mount" # if your find uses "-mount" WHERE="$1 -xdev" # if your find uses "-xdev" fi TEMP=/tmp/top-ten-files.$$ find $WHERE -type f -exec /bin/ls -s {} ';' sort -nr head awk '{ print $2 }' > $TEMP for file in `cat $TEMP` do DETAILS=` ls -l $file awk '{ print $3 " " $4 }'` echo $file $DETAILS done rm -f $TEMP exit 0 The End 14