plymouth initramfs-hook breaks SSH cryptroot unlocking via dropbear

[Matthias Andree]

Binary package hint: plymouth

Plymouth's initramfs-hook creates a /etc/passwd line for root, in order to remedy https://bugs.launchpad.net/ubuntu/+source/plymouth/+bug/649917 - however, it sets an invalid shell, namely /bin/bash. This makes it impossible to log into the initramfs's dropbear as root: dropbear refuses the login due to an invalid shell. This can cause users to get locked out of their machines if only installing plymouth and suffering from a power outage.

In cryptroot setups where dropbear is installed, the dropbear hook has previously created an /etc/passwd line for root that sets the proper /bin/sh shell.

Please fix plymouth to either set a valid shell, or not to stomp over existing ${DESTDIR}/etc/passwd configurations ASAP.

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: plymouth 0.8.2-2ubuntu5.1 [modified: usr/share/initramfs-tools/hooks/plymouth]
ProcVersionSignature: Ubuntu 2.6.35-27.48-generic 2.6.35.11
Uname: Linux 2.6.35-27-generic x86_64
NonfreeKernelModules: fglrx
Architecture: amd64
Date: Fri Mar 11 14:37:48 2011
DefaultPlymouth: /lib/plymouth/themes/ubuntu-logo/ubuntu-logo.plymouth
MachineType: System manufacturer System Product Name
ProcCmdLine: root=/dev/mapper/vgcrypt0-root ro ip=192.168.0.4::192.168.0.253::hostname:eth0:none vga=794 quiet splash
ProcEnviron:
 PATH=(custom, no user)
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
ProcFB: 0 VESA VGA
SourcePackage: plymouth
TextPlymouth: /lib/plymouth/themes/ubuntu-text/ubuntu-text.plymouth

[Matthias Andree (matthias-andree)]

Note that the "modified" file in the package contains the fix (see attached patch) and has been successfully tested.

[Jamie Strandboge (jdstrand)]

Thanks for taking the time to report this bug and helping to make Ubuntu better. We appreciate the difficulties you are facing, but this appears to be a "regular" (non-security) bug. I have unmarked it as a security issue since this bug does not show evidence of allowing attackers to cross privilege boundaries nor directly cause loss of data/privacy. Please feel free to report any other bugs you may find.

[Matthias Andree (matthias-andree)]

It would seem that installing plymouth breaks the system and prevents remote logins (denial of service) even to admins, possibly incurring travel necessities to a colocation center hundreds of km away...
I had discussed this with fellow admins before flagging it as security.
--
Matthias Andree