Subject: CVE-2022-48629: crypto: qcom-rng - ensure buffer for generate is completely filled

From: Greg Kroah-Hartman <[email-masked]>

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).

The Linux kernel CVE team has assigned CVE-2022-48629 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 4.19 with commit ceec5f5b5988 and fixed in 4.19.236 with commit a8e32bbb96c2
	Issue introduced in 4.19 with commit ceec5f5b5988 and fixed in 5.4.187 with commit 184f7bd08ce5
	Issue introduced in 4.19 with commit ceec5f5b5988 and fixed in 5.10.108 with commit 0f9b7b8df175
	Issue introduced in 4.19 with commit ceec5f5b5988 and fixed in 5.15.31 with commit ab9337c7cb6f
	Issue introduced in 4.19 with commit ceec5f5b5988 and fixed in 5.16.17 with commit 485995cbc98a
	Issue introduced in 4.19 with commit ceec5f5b5988 and fixed in 5.17 with commit a680b1832ced

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2022-48629
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	drivers/crypto/qcom-rng.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/a8e32bbb96c25b7ab29b1894dcd45e0b3b08fd9d
	https://git.kernel.org/stable/c/184f7bd08ce56f003530fc19f160d54e75bf5c9d
	https://git.kernel.org/stable/c/0f9b7b8df17525e464294c916acc8194ce38446b
	https://git.kernel.org/stable/c/ab9337c7cb6f875b6286440b1adfbeeef2b2b2bd
	https://git.kernel.org/stable/c/485995cbc98a4f77cfd4f8ed4dd7ff8ab262964d
	https://git.kernel.org/stable/c/a680b1832ced3b5fa7c93484248fd221ea0d614b