Hello, On Wednesday, May 27, 2020 3:44:13 PM EDT Vishnu Srinivasa Ramaprasad wrote: > I'm Vish and I am a newbie to auditd. My requirement is to log only > shell/bash commands and custom commands executed by administrator users. > I have created these rules in /etc/audit/rules.d/audit.rules, to ensure > SYSCALL, EXECVE are being added to audit.log for administrator users with > auid greater than 1000: > -a exit,always -F arch=b64 -S execve -F auid>=1000 -F auid!=-1 -k log_cmd > -a exit,always -F arch=b32 -S execve -F auid>=1000 -F auid!=-1 -k log_cmd > > After restarting auditd service, I had executed strace on a simple command > which will display version of my project's toolkit: > > ~# strace -e trace=execve toolkit-version-show > execve("/var/tmp/toolkit-version-show", ["toolkit-version-show"], > 0x7ffef1fa38b0 /* 30 vars */) = 0 > Toolkit Version: 1.01 > +++ exited with 0 +++ > > Later, I executed the ausearch command to check the log entry: > ~# ausearch -i --start recent > ---- > type=EXECVE msg=audit(05/27/2020 19:01:26.605:12725) : argc=2 > a0=/usr/bin/perl a1=/var/tmp/toolkit-version-show > type=SYSCALL msg=audit(05/27/2020 19:01:26.605:12725) : arch=x86_64 > syscall=execve success=yes exit=0 a0=0x7ffef1fa2450 a1=0x7ffef1fa38a0 > a2=0x7ffef1fa38b0 a3=0x7f47f8669740 items=3 ppid=3641 pid=3643 > auid=administrator uid=root gid=root euid=root suid=root fsuid=root > egid=root sgid=root fsgid=root tty=pts0 ses=8936 comm=toolkit-version-sho > exe=/usr/bin/perl key=log_cmd > ---- > type=EXECVE msg=audit(05/27/2020 19:01:26.601:12724) : argc=4 a0=strace > a1=-e a2=trace=execve a3=toolkit-version-show > type=SYSCALL msg=audit(05/27/2020 19:01:26.601:12724) : arch=x86_64 > syscall=execve success=yes exit=0 a0=0x55a2d44c9010 a1=0x55a2d449fe80 > a2=0x55a2d4389490 a3=0x8 items=2 ppid=3099 pid=3641 auid=administrator > uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root > fsgid=root tty=pts0 ses=8936 comm=strace exe=/usr/bin/strace key=log_cmd > ---- > > My understanding of a0 - a2: Please refer the syntax of execve() : > > int execve(const char*filename, char *const argv[], char *const envp[]); > > Based on syntax of execve() and output from strace, I could understand that > in audit.log event entry: > a0=0x7ffef1fa2450 represents filename argument of execve It a pointer to the string. > a1=0x7ffef1fa38a0 represents argv[] argument of execve > a2=0x7ffef1fa38b0 represents envp[] argument of execve > > Question 1: What does the a3=0x7f47f8669740 value represent? whatever is on the stack in that position. > As execve() has only 3 arguments (represented by a0,a1,a2), what value gets > stored in a3? > I have noticed a3 values to be varying from: > a3=0x0 > a3=0x7 > a3=0x55a2d4389490 > a3=0x56a2d44adc00 > a3=0x8 > > Question 2: a3=0x8 seems to be the value assigned for a majority of > execve() syscalls. > Is this a standard value set in case of main/primary system call, such as > toolkit-version-show? Nope. It depends entirely on what the previous syscalls or system activity were and where on the stack it currently is. > Could I use this in a rule filter *-F a3=8* to log only primary (custom > script) command executed by user and not internal commands executed by > custom script like ls, cat, grep.. etc.: > -a exit,always -F arch=b64 -S execve *-F a3=8* -F auid>=1000 -F auid!=-1 -k > log_cmd > -a exit,always -F arch=b32 -S execve *-F a3=8* -F auid>=1000 -F auid!=-1 -k > log_cmd > > Would I miss logging a few primary syscalls, if a3 is not 0x80 in some > cases? Nope. you can't count on anything in a3 since it is not valid for that syscall. > Question 3: If a3=0x8 is not a standard value, Is it possible to identify > primary custom command and log only that command, and not internal commands > with a3=0x0 or a3=0x55a2d4389490? You can always place a watch on the custom commands. -a exit,always -F path=/path-to/custom-command -F perm=x -F key=command > Question 4: Is it possible to filter out and not log syscalls with > tty=(none)? No. But there is a loose correlation with auid or sessionid being -1. That means it is a daemon. And if you only want commands run by people, then you want -F auid>=1000 -F auid!=-1. -Steve