Tracking file deletion using auditd without unlink?

Question

I'm working on creating an auditd rule that will track the deletion of files and directories. I have one that often turns up in online searches but I'm not sure it is really all that useful:

-a exit,always -F arch=b32 -S unlink -S rmdir -k deletion

There are actually two. One each for 32-bit and 64-bit.

The problem I have is that I don't know of anyone who uses unlink to delete files instead of rm. I've tested rm thinking maybe it actually called unlink but nothing shows up in the log.

Am I missing something? Is there a way to track file deletions using rm?

Answer 1

I ran strace rm test to see if it was making any calls to unlink. It isn't calling unlink itself, but instead unlinkat. I've added that to the auditd rule:

-a exit,always -F arch=b32 -S unlink -S unlinkat -S rmdir -k deletion

This will trigger on any file deletion whether by root or a regular user.

The strace output:

execve("/bin/rm", ["rm", "test"], [/* 17 vars */]) = 0
brk(0)                                  = 0x60d000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3a8e43c000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY)      = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=26788, ...}) = 0
mmap(NULL, 26788, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3a8e435000
close(3)                                = 0
open("/lib64/libc.so.6", O_RDONLY)      = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0p\356\0015;\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1926760, ...}) = 0
mmap(0x3b35000000, 3750152, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x3b35000000
mprotect(0x3b3518a000, 2097152, PROT_NONE) = 0
mmap(0x3b3538a000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x18a000) = 0x3b3538a000
mmap(0x3b3538f000, 18696, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x3b3538f000
close(3)                                = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3a8e434000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3a8e433000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3a8e432000
arch_prctl(ARCH_SET_FS, 0x7f3a8e433700) = 0
mprotect(0x3b3538a000, 16384, PROT_READ) = 0
mprotect(0x3b34a1f000, 4096, PROT_READ) = 0
munmap(0x7f3a8e435000, 26788)           = 0
brk(0)                                  = 0x60d000
brk(0x62e000)                           = 0x62e000
open("/usr/lib/locale/locale-archive", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=99158576, ...}) = 0
mmap(NULL, 99158576, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3a885a1000
close(3)                                = 0
ioctl(0, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
newfstatat(AT_FDCWD, "test", {st_mode=S_IFREG|0640, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0
geteuid()                               = 0
unlinkat(AT_FDCWD, "test", 0)           = 0
close(0)                                = 0
close(1)                                = 0
close(2)                                = 0
exit_group(0)                           = ?