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Bug 1211406 - rngd assume all entropy to be 8-bit
Summary: rngd assume all entropy to be 8-bit
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: rng-tools
Version: 7.1
Hardware: All
OS: Linux
unspecified
medium
Target Milestone: rc
: ---
Assignee: Neil Horman
QA Contact: Vilém Maršík
URL: https://sourceforge.net/p/gkernel/bug...
Whiteboard:
Depends On:
Blocks: 1254223
TreeView+ depends on / blocked
 
Reported: 2015-04-13 23:10 UTC by Yi Hao
Modified: 2015-11-19 03:30 UTC (History)
3 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of:
Environment:
Last Closed: 2015-11-19 03:30:51 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)
patch to add entropy count option (1.49 KB, patch)
2015-04-14 13:48 UTC, Neil Horman 		no flags Details | Diff
stap probe (1.43 KB, text/plain)
2015-08-18 15:54 UTC, Vilém Maršík 		no flags Details
View All


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHBA-2015:2179 0 normal SHIPPED_LIVE rng-tools bug fix update 2015-11-19 07:40:29 UTC

Description Yi Hao 2015-04-13 23:10:02 UTC 
Description of problem:
random_add_entropy() hardcoded entropy count as 8 bit per byte. There is no known hardware entropy generator in the market that has 8 bit per byte of entropy.

Version-Release number of selected component (if applicable):
rng-tools-5-2.el7

How reproducible:
Every time

Steps to Reproduce:
1.
2.
3.

Actual results:


Expected results:


Additional info:
It would be better to use safer value such as 7 instead of 8. Alternatively, allow user to specify the entropy as command line parameter
Comment 2 Neil Horman 2015-04-14 13:48:04 UTC 
Created attachment 1014318 [details]
patch to add entropy count option

Untested, please let me know if this works for you.  Thanks.
Comment 3 Yi Hao 2015-04-14 16:17:14 UTC 
Hi,
Thanks for the patch.

if ((sscanf(arg,"%i", &e) == 0) || (e < 0) || (e > 8))
Actually should be (e < 1)
Missing manpage entry.

Other than that looks fine.
Comment 5 Vilém Maršík 2015-08-11 16:39:32 UTC 
I cannot see the new switch documented in the man page (see Comment #3). Did it get lost during the process?
Comment 6 Neil Horman 2015-08-11 18:53:42 UTC 
didn't add it to the documentation, I'll do that in a separate patch
Comment 7 Vilém Maršík 2015-08-18 15:53:38 UTC 
Used a Systemtap probe to see what data are sent. From what I know about the entropy pool, it rather looks correct - kernel entropy count is increased by (number of data added) * (number you specified by '-e' option) :

rngd -f -e 1:
Tue Aug 18 15:13:03 2015 :: rngd
  ioctl("/dev/random", RNDADDENTROPY, {entropy_count = 64, buf_size= 64})
...

rngd -f -e 8:
Tue Aug 18 15:13:12 2015 :: rngd
  ioctl("/dev/random", RNDADDENTROPY, {entropy_count = 512, buf_size= 64})
...
Comment 8 Vilém Maršík 2015-08-18 15:54:54 UTC 
Created attachment 1064370 [details]
stap probe

thanks to Jeffrey Bastian and Will Cohen
Comment 10 errata-xmlrpc 2015-11-19 03:30:51 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2015-2179.html
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