CVE-2022-48629

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).

Notes