Bug#897572: plymouth: long delay before splashscreen with kernel 4.16

[Ben Caradoc-Davies]

Ben,

even though X is not involved, you are right on the money about this 
being caused by waiting for random bits. This is a kernel bug caused by 
urandom blocking when it should not. I will merge the issues when I have 
my final patch ready.


You can see the "random: plymouthd: uninitialized urandom read" warning 
in my screen photo:

https://bugs.debian.org/cgi-bin/bugreport.cgi?att=1;bug=897572;filename=img_20180504_120059.jpg;msg=37

This bug is introduced by the "crng_init > 0" to "crng_init > 1" change 
in this commit:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=43838a23a05fbd13e47d750d3dfd77001536dd33

This change inadvertently impacts urandom_read, causing the crng_init==1 
state to be treated as uninitialized and causing urandom to block, 
despite this state existing *specifically* to support non-cryptographic 
needs at boot time:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/char/random.c#n1863

Reverting 43838a23a05f ("random: fix crng_ready() test") fixes the bug 
(tested with 4.16.5-1), but this may cause security concerns 
(CVE-2018-1108 is mentioned in 43838a23a05f). I am testing a more 
localised fix that should be more palatable to upstream.


Kind regards,

--
Ben Caradoc-Davies 
Director
Transient Software Limited 
New Zealand

Bug#897572: plymouth: long delay before splashscreen with kernel 4.16

[at46]

You are right. Seems to be the same bug. I thought that since everything 
works fine without plymouth that it should be fixed there but now I am 
not sure anymore. Also I'm not so familiar with debian bug tracker. Can 
or should I mark it as duplicate somehow or merge it with your bug report?



Am 06.05.2018 um 03:01 schrieb Ben Caradoc-Davies:
Looks like the same bug. We should probably merge, but into what 
package (linux, plymouth, or xorg)?:


Bug#897958: plymouth: long delay before splashscreen with kernel 4.16
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=897958

Bug#897572: linux-image-4.16.0-1-amd64 breaks plymouth LUKS prompt
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=897572

Ben Hutchings suggests that this is probably caused by the new RNG 
behaviour in 4.16, and I concur. See Ben's remarks in #897572 
.


Kind regards,

Bug#897572: plymouth: long delay before splashscreen with kernel 4.16

[Ben Caradoc-Davies]

Looks like the same bug. We should probably merge, but into what package 
(linux, plymouth, or xorg)?:


Bug#897958: plymouth: long delay before splashscreen with kernel 4.16
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=897958

Bug#897572: linux-image-4.16.0-1-amd64 breaks plymouth LUKS prompt
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=897572

Ben Hutchings suggests that this is probably caused by the new RNG 
behaviour in 4.16, and I concur. See Ben's remarks in #897572 
.


Kind regards,

--
Ben Caradoc-Davies 
Director
Transient Software Limited 
New Zealand