Arch Linux

Leonid.I

Member

From: Aethyr

Registered: 2009-03-22

Posts: 999

chkrootkit's chkdir reports possible LKM trojan installed

Hi,

On a fresh install of arch i686 chkrootkit reports

checking   lkm ... chkproc: nothing detected
-37          /usr/share
-2            /usr/bin
-1            /usr/sbin
-8            /lib
chkdirs: Warning: Possible LKM Trojan installed

This is a minimal testing system (btrfs, systemd, pacman 4, etc...) running in KVM. Meanwhile, on the arch x86_64 host (ext4 root), chkdirs is clean.

According to chkdirs.c, this program simply reports the link count discrepancy, and I suspect it fails because of btrfs... Is there any way to see which files exactly it complains about?

Thanks.

EDIT: Also, in the testing system rkhunter is clean, but I'm not sure if it poerforms exactly same checks...

Last edited by Leonid.I (2011-09-10 23:10:55)

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Seb35

Member

Registered: 2020-12-07

Posts: 2

Re: chkrootkit's chkdir reports possible LKM trojan installed

On a btrfs filesystem the test 'lkm' of chkrootkit will always be positive (consequently it is not useful to detect a possible rootkit: it is at least a false positive but possibly a true positive) because st_nlink’s value on directories is always 1, on the contrary of other filesystems. The value indicated by chkdirs is always -(1+numberOfSubDirectories) on a btrfs filesystem.

See this discussion (the referenced patch was rejected, but I did not dive to understand exactly what it was) as well as the note in conclusion of this blog post.

Seb35

Member

Registered: 2020-12-07

Posts: 2

Re: chkrootkit's chkdir reports possible LKM trojan installed

I reported the issue to the author, Nelson, and he fixed it in version 0.54 released on 2020-12-24.

2ManyDogs

Forum Fellow

Registered: 2012-01-15

Posts: 4,645

Re: chkrootkit's chkdir reports possible LKM trojan installed

Thanks for the contribution, but this topic is very old and the OP has not been back since 2019.

Closing.