HDFS-15910. Improve security with explicit_bzero

[GauthamBanasandra]

• Replacing bzero with explicit_bezero since it
  is more secure.
• explicit_bzero guarantees that the buffer is
  cleared irrespective of the compiler optimization,
  unlike bzero.

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	0m 33s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 1s		codespell was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
-1 ❌	test4tests	0m 0s		The patch doesn't appear to include any new or modified tests. Please justify why no new tests are needed for this patch. Also please list what manual steps were performed to verify this patch.
			_ trunk Compile Tests _
+1 💚	mvninstall	33m 1s		trunk passed
+1 💚	compile	2m 35s		trunk passed with JDK Ubuntu-11.0.10+9-Ubuntu-0ubuntu1.20.04
+1 💚	compile	2m 43s		trunk passed with JDK Private Build-1.8.0_282-8u282-b08-0ubuntu1~20.04-b08
+1 💚	mvnsite	0m 27s		trunk passed
+1 💚	shadedclient	52m 6s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	0m 16s		the patch passed
+1 💚	compile	2m 29s		the patch passed with JDK Ubuntu-11.0.10+9-Ubuntu-0ubuntu1.20.04
-1 ❌	cc	2m 29s	/results-compile-cc-hadoop-hdfs-project_hadoop-hdfs-native-client-jdkUbuntu-11.0.10+9-Ubuntu-0ubuntu1.20.04.txt	hadoop-hdfs-project_hadoop-hdfs-native-client-jdkUbuntu-11.0.10+9-Ubuntu-0ubuntu1.20.04 with JDK Ubuntu-11.0.10+9-Ubuntu-0ubuntu1.20.04 generated 11 new + 82 unchanged - 11 fixed = 93 total (was 93)
+1 💚	golang	2m 29s		the patch passed
+1 💚	javac	2m 29s		the patch passed
+1 💚	compile	2m 29s		the patch passed with JDK Private Build-1.8.0_282-8u282-b08-0ubuntu1~20.04-b08
-1 ❌	cc	2m 29s	/results-compile-cc-hadoop-hdfs-project_hadoop-hdfs-native-client-jdkPrivateBuild-1.8.0_282-8u282-b08-0ubuntu1~20.04-b08.txt	hadoop-hdfs-project_hadoop-hdfs-native-client-jdkPrivateBuild-1.8.0_282-8u282-b08-0ubuntu120.04-b08 with JDK Private Build-1.8.0_282-8u282-b08-0ubuntu120.04-b08 generated 14 new + 79 unchanged - 14 fixed = 93 total (was 93)
+1 💚	golang	2m 29s		the patch passed
+1 💚	javac	2m 29s		the patch passed
+1 💚	blanks	0m 1s		The patch has no blanks issues.
+1 💚	mvnsite	0m 19s		the patch passed
+1 💚	shadedclient	13m 15s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	31m 33s		hadoop-hdfs-native-client in the patch passed.
+1 💚	asflicense	0m 34s		The patch does not generate ASF License warnings.
		105m 50s

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-2793/1/artifact/out/Dockerfile
GITHUB PR	#2793
Optional Tests	dupname asflicense compile cc mvnsite javac unit codespell golang
uname	Linux b7cfd159c732 4.15.0-60-generic #67-Ubuntu SMP Thu Aug 22 16:55:30 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / b6c2605
Default Java	Private Build-1.8.0_282-8u282-b08-0ubuntu1~20.04-b08
Multi-JDK versions	/usr/lib/jvm/java-11-openjdk-amd64:Ubuntu-11.0.10+9-Ubuntu-0ubuntu1.20.04 /usr/lib/jvm/java-8-openjdk-amd64:Private Build-1.8.0_282-8u282-b08-0ubuntu1~20.04-b08
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-2793/1/testReport/
Max. process+thread count	540 (vs. ulimit of 5500)
modules	C: hadoop-hdfs-project/hadoop-hdfs-native-client U: hadoop-hdfs-project/hadoop-hdfs-native-client
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-2793/1/console
versions	git=2.25.1 maven=3.6.3
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[goiri]

Thanks @GauthamBanasandra for the patch.
Can you add some links describing the advantages of explicit bzero you mentioned?

[GauthamBanasandra]

This page describes why we should prefer using explicit_bzero over bzero - https://www.gnu.org/software/libc/manual/html_node/Erasing-Sensitive-Data.html.