in_docker: fix error handling if some resources not found

[nokute78]

This patch is to add NULL check to prevent SIGSEGV which is reported at #5149

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Enter [N/A] in the box, if an item is not applicable to your change.

Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change
• Debug log output from testing the change

• Attached Valgrind output that shows no leaks or memory corruption was found

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• [N/A] Attached local packaging test output showing all targets (including any new ones) build.

Documentation

• [N/A] Documentation required for this feature

Backporting

• [N/A] Backport to latest stable release.

Configuration

1. Run a container.
2. sudo fluent-bit -i docker -o stdout

Debug log

I tested renaming invalid cpu resource file name.

diff --git a/plugins/in_docker/docker.h b/plugins/in_docker/docker.h
index 98a9a94ed..317264d7d 100644
--- a/plugins/in_docker/docker.h
+++ b/plugins/in_docker/docker.h
@@ -35,7 +35,7 @@
 #define DOCKER_CGROUP_CPU_DIR "/sys/fs/cgroup/cpu/docker"
 #define DOCKER_MEM_LIMIT_FILE "memory.limit_in_bytes"
 #define DOCKER_MEM_USAGE_FILE "memory.usage_in_bytes"
-#define DOCKER_CPU_USAGE_FILE "cpuacct.usage"
+#define DOCKER_CPU_USAGE_FILE "cpuacct.usagd"
 #define DOCKER_LIB_ROOT       "/var/lib/docker/containers"
 #define DOCKER_CONFIG_JSON    "config.v2.json"
 #define DOCKER_NAME_ARG       "\"Name\""

No SIGSEGVs.

$ sudo bin/fluent-bit -i docker -o stdout
Fluent Bit v1.9.1
* Copyright (C) 2015-2021 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2022/03/26 09:09:06] [ info] [fluent bit] version=1.9.1, commit=1b89b4711b, pid=37257
[2022/03/26 09:09:06] [ info] [storage] version=1.1.6, type=memory-only, sync=normal, checksum=disabled, max_chunks_up=128
[2022/03/26 09:09:06] [ info] [cmetrics] version=0.3.0
[2022/03/26 09:09:06] [ info] [sp] stream processor started
[2022/03/26 09:09:06] [ info] [output:stdout:stdout.0] worker #0 started
[2022/03/26 09:09:07] [error] [plugins/in_docker/docker.c:315 errno=2] No such file or directory
[2022/03/26 09:09:07] [error] [input:docker:docker.0] error gathering CPU data from /sys/fs/cgroup/cpu/docker/58c33a47212e777cafb7014e44aa6c829b09a62f5f7e3aa316fd5c5144bce2be/cpuacct.usagd
[2022/03/26 09:09:08] [error] [plugins/in_docker/docker.c:315 errno=2] No such file or directory
[2022/03/26 09:09:08] [error] [input:docker:docker.0] error gathering CPU data from /sys/fs/cgroup/cpu/docker/58c33a47212e777cafb7014e44aa6c829b09a62f5f7e3aa316fd5c5144bce2be/cpuacct.usagd
[2022/03/26 09:09:09] [error] [plugins/in_docker/docker.c:315 errno=2] No such file or directory
[2022/03/26 09:09:09] [error] [input:docker:docker.0] error gathering CPU data from /sys/fs/cgroup/cpu/docker/58c33a47212e777cafb7014e44aa6c829b09a62f5f7e3aa316fd5c5144bce2be/cpuacct.usagd
^C[2022/03/26 09:09:09] [engine] caught signal (SIGINT)
[2022/03/26 09:09:09] [ info] [input] pausing docker.0
[2022/03/26 09:09:09] [ warn] [engine] service will shutdown in max 5 seconds
[2022/03/26 09:09:10] [ info] [engine] service has stopped (0 pending tasks)
[2022/03/26 09:09:10] [ info] [output:stdout:stdout.0] thread worker #0 stopping...
[2022/03/26 09:09:10] [ info] [output:stdout:stdout.0] thread worker #0 stopped

Valgrind output

$ sudo valgrind --leak-check=full bin/fluent-bit -i docker -o stdout
==37262== Memcheck, a memory error detector
==37262== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==37262== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==37262== Command: bin/fluent-bit -i docker -o stdout
==37262== 
Fluent Bit v1.9.1
* Copyright (C) 2015-2021 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2022/03/26 09:09:44] [ info] [fluent bit] version=1.9.1, commit=1b89b4711b, pid=37262
[2022/03/26 09:09:44] [ info] [storage] version=1.1.6, type=memory-only, sync=normal, checksum=disabled, max_chunks_up=128
[2022/03/26 09:09:44] [ info] [cmetrics] version=0.3.0
[2022/03/26 09:09:44] [ info] [sp] stream processor started
[2022/03/26 09:09:44] [ info] [output:stdout:stdout.0] worker #0 started
[2022/03/26 09:09:45] [error] [plugins/in_docker/docker.c:315 errno=2] No such file or directory
[2022/03/26 09:09:45] [error] [input:docker:docker.0] error gathering CPU data from /sys/fs/cgroup/cpu/docker/58c33a47212e777cafb7014e44aa6c829b09a62f5f7e3aa316fd5c5144bce2be/cpuacct.usagd
[2022/03/26 09:09:46] [error] [plugins/in_docker/docker.c:315 errno=2] No such file or directory
[2022/03/26 09:09:46] [error] [input:docker:docker.0] error gathering CPU data from /sys/fs/cgroup/cpu/docker/58c33a47212e777cafb7014e44aa6c829b09a62f5f7e3aa316fd5c5144bce2be/cpuacct.usagd
^C[2022/03/26 09:09:46] [engine] caught signal (SIGINT)
[2022/03/26 09:09:46] [ info] [input] pausing docker.0
[2022/03/26 09:09:46] [ warn] [engine] service will shutdown in max 5 seconds
[2022/03/26 09:09:47] [ info] [engine] service has stopped (0 pending tasks)
[2022/03/26 09:09:47] [ info] [output:stdout:stdout.0] thread worker #0 stopping...
[2022/03/26 09:09:47] [ info] [output:stdout:stdout.0] thread worker #0 stopped
==37262== 
==37262== HEAP SUMMARY:
==37262==     in use at exit: 0 bytes in 0 blocks
==37262==   total heap usage: 1,066 allocs, 1,066 frees, 315,501 bytes allocated
==37262== 
==37262== All heap blocks were freed -- no leaks are possible
==37262== 
==37262== For lists of detected and suppressed errors, rerun with: -s
==37262== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

[nokute78]

Note: https://github.com/fluent/fluent-bit/blob/v1.9.0/plugins/in_docker/docker.c#L576