Affected: Linux

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 f…