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Groups > linux.debian.bugs.dist > #914362

Bug#907060: linux: ratelimiting hides warnings about uninitialized crng usage

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Source: linux-image-4.17.0-3-amd64
Version: 4.17.17-1
Severity: normal

A minute or so after booting this kernel within a kvm guest that has
some userspace crypto working in it, i see a message about ratelimited
reports in the kernel ring buffer, but i never get any of the
full messages:

root@test:~# head -v /proc/sys/kernel/printk*
==> /proc/sys/kernel/printk <==
7       4       1       7

==> /proc/sys/kernel/printk_delay <==

0

==> /proc/sys/kernel/printk_devkmsg <==
ratelimit

==> /proc/sys/kernel/printk_ratelimit <==
10

==> /proc/sys/kernel/printk_ratelimit_burst <==
10
root@test:~# cat /proc/cmdline 
BOOT_IMAGE=/boot/vmlinuz-4.17.0-3-amd64 root=UUID=44659876-4a68-4a3a-b3fa-0403eeb0c6ca
 ro console=ttyS0,115200n8
root@test:~# dmesg | tail -n 3
[    2.880287] [drm] Initialized bochs-drm 1.0.0 20130925 for 0000:00:02.0 on minor 0
[  107.680402] random: crng init done
[  107.681132] random: 7 urandom warning(s) missed due to ratelimiting
root@test:~# 

given the timing, i presume the urandom warnings have to do with some
process accessing /dev/urandom before the crng is initialized, but
none of them is displayed (not even one, let alone the 10 i'd expect
from the sysctl values).

This is a problem because it makes it harder to figure out which
processes are actually doing the dangerous urandom reads.

This system doesn't have plymouth or anything graphical installed
(it's using a virtualized serial console) so i don't think #897572 is
related.

          --dkg


-- System Information:
Debian Release: sid
Architecture: amd64 (x86_64)

Kernel: Linux 4.17.0-3-amd64 (SMP w/1 CPU core)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

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Bug#907060: linux: ratelimiting hides warnings about uninitialized crng usage Daniel Kahn Gillmor <dkg@fifthhorseman.net> - 2018-08-23 17:40 +0200

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