Bug in cpio causing problems in dracut initramfs tools

[Robert Rochford]

Hi,

 

A summary of the bug in cpio is like this:

 

Details:

 

Using dracut, my initramfs-4.1.12-112.16.4.el7uek.x86_64.img picks up contents from the drive from two separate identical files, and creates a gzip+cpio file with the following contents:

'etc/sysctl.conf'

'etc/sysctl.d/99-oracle-database-server-12cR2-preinstall-sysctl.conf'

 

Inside the cpio archive:

'etc/sysctl.conf' [this is a hard link to the other file]

'etc/sysctl.d/99-oracle-database-server-12cR2-preinstall-sysctl.conf'

 

The dracut package lsinitrd can be used to verify the contents of a initramfs file using a command such as

 

lsinitrd -f /etc/sysctl.conf

 

With this bug, lsinitrd -f returns no data.

 

Diagnosis:

 

Internally, lsinitrd calls the following (command cut down for brevity)

 

zcat initramfs-4.1.12-112.16.4.el7uek.x86_64.img 2>/dev/null | cpio --extract --verbose --quiet --to-stdout etc/sysctl.conf

 

Inside the archive, etc/sysctl.conf is a hard link to the other file in the archive, and is therefore of file size zero.

 

Bug:

 

When cpio extracts a file to stdout, it should follow hard linked files and output the hard link data. Hard linked files are equivalent. It’s not as if File A is linked to File B. File A and file B are the same file. The should both extract to the same data.

 

Effect:

 

I spent a long time trying to determine why my initramfs file had an empty sysctl.conf, when there was no real problem. The instruction here https://access.redhat.com/solutions/2798411 uncovered this bug via the following step:

Verify that the initramfs contains the /etc/sysctl.conf file and matches the one on the system

# diff -u /etc/sysctl.conf <(lsinitrd -f /etc/sysctl.co

 

 

 

 

Kind Regards,

 

Robert

 

 

Robert Rochford | Vice President Programme Development
Constraint Technologies International
Level 9, 456 Lonsdale Street, Melbourne 3000 Australia
+61 3 9604 9822 (direct)
address@hidden

www.constrainttec.com

 

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