title: crypto: qcom-rng - ensure buffer for generate is completely filled
description: In the Linux kernel, the following vulnerability has been resolved:
crypto: qcom-rng - ensure buffer for generate is completely filled
The generate function in struct rng_alg expects that the destination
buffer is completely filled if the function returns 0. qcom_rng_read()
can run into a situation where the buffer is partially filled with
randomness and the remaining part of the buffer is zeroed since
qcom_rng_generate() doesn't check the return value. This issue can
be reproduced by running the following from libkcapi:
kcapi-rng -b 9000000 > OUTFILE
The generated OUTFILE will have three huge sections that contain all
zeros, and this is caused by the code where the test
'val & PRNG_STATUS_DATA_AVAIL' fails.
Let's fix this issue by ensuring that qcom_rng_read() always returns
with a full buffer if the function returns success. Let's also have
qcom_rng_generate() return the correct value.
Here's some statistics from the ent project
(https://www.fourmilab.ch/random/) that shows information about the
quality of the generated numbers:
$ ent -c qcom-random-before
Value Char Occurrences Fraction
0           606748   0.067416
1            33104   0.003678
2            33001   0.003667
...
253   �        32883   0.003654
254   �        33035   0.003671
255   �        33239   0.003693
Total:       9000000   1.000000
Entropy = 7.811590 bits per byte.
Optimum compression would reduce the size
of this 9000000 byte file by 2 percent.
Chi square distribution for 9000000 samples is 9329962.81, and
randomly would exceed this value less than 0.01 percent of the
times.
Arithmetic mean value of data bytes is 119.3731 (127.5 = random).
Monte Carlo value for Pi is 3.197293333 (error 1.77 percent).
Serial correlation coefficient is 0.159130 (totally uncorrelated =
0.0).
Without this patch, the results of the chi-square test is 0.01%, and
the numbers are certainly not random according to ent's project page.
The results improve with this patch:
$ ent -c qcom-random-after
Value Char Occurrences Fraction
0            35432   0.003937
1            35127   0.003903
2            35424   0.003936
...
253   �        35201   0.003911
254   �        34835   0.003871
255   �        35368   0.003930
Total:       9000000   1.000000
Entropy = 7.999979 bits per byte.
Optimum compression would reduce the size
of this 9000000 byte file by 0 percent.
Chi square distribution for 9000000 samples is 258.77, and randomly
would exceed this value 42.24 percent of the times.
Arithmetic mean value of data bytes is 127.5006 (127.5 = random).
Monte Carlo value for Pi is 3.141277333 (error 0.01 percent).
Serial correlation coefficient is 0.000468 (totally uncorrelated =
0.0).
This change was tested on a Nexus 5 phone (msm8974 SoC).
affected:
{
product: Linux
vendor: Linux
defaultStatus: unaffected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions:
version: ceec5f5b5988, lessThan: a8e32bbb96c2, status: affected, versionType: git
version: ceec5f5b5988, lessThan: 184f7bd08ce5, status: affected, versionType: git
version: ceec5f5b5988, lessThan: 0f9b7b8df175, status: affected, versionType: git
version: ceec5f5b5988, lessThan: ab9337c7cb6f, status: affected, versionType: git
version: ceec5f5b5988, lessThan: 485995cbc98a, status: affected, versionType: git
version: ceec5f5b5988, lessThan: a680b1832ced, status: affected, versionType: git
}
{
product: Linux
vendor: Linux
defaultStatus: affected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions:
version: 4.19, status: affected
version: 0, lessThan: 4.19, status: unaffected, versionType: custom
version: 4.19.236, lessThanOrEqual: 4.19.*, status: unaffected, versionType: custom
version: 5.4.187, lessThanOrEqual: 5.4.*, status: unaffected, versionType: custom
version: 5.10.108, lessThanOrEqual: 5.10.*, status: unaffected, versionType: custom
version: 5.15.31, lessThanOrEqual: 5.15.*, status: unaffected, versionType: custom
version: 5.16.17, lessThanOrEqual: 5.16.*, status: unaffected, versionType: custom
version: 5.17, lessThanOrEqual: *, status: unaffected, versionType: original_commit_for_fix
}
