collector SIGSEGV

[fld-opensource]

Describe the bug
Using the nginx receiver, where nginx is not present, we dereference invalid pointer.

Steps to reproduce
$> opentelemetry-collector-builder --config the_following_yaml

What did you expect to see?
Not a crash :)

What did you see instead?

2021-03-16T13:01:28.110+0100 INFO service/service.go:267 Everything is ready. Begin running and processing data.
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xffc676]

goroutine 112 [running]:
go.opentelemetry.io/collector/consumer/pdata.ResourceMetricsSlice.Len(...)
go.opentelemetry.io/collector@v0.22.0/consumer/pdata/generated_metrics.go:52
go.opentelemetry.io/collector/receiver/scraperhelper.metricCount(0x0, 0xc00077f1a0)
go.opentelemetry.io/collector@v0.22.0/receiver/scraperhelper/scraper.go:160 +0x26
go.opentelemetry.io/collector/receiver/scraperhelper.resourceMetricsScraper.Scrape(0x34db9e0, 0xc00058b4d0, 0x2e73235, 0x5, 0xc00058b4b0, 0x3520460, 0xc00077f1a0, 0xc0002685c8, 0x5, 0x0, ...)
go.opentelemetry.io/collector@v0.22.0/receiver/scraperhelper/scraper.go:153 +0x110
go.opentelemetry.io/collector/receiver/scraperhelper.(*controller).scrapeMetricsAndReport(0xc00042e0e0, 0x35203e0, 0xc000120000)
go.opentelemetry.io/collector@v0.22.0/receiver/scraperhelper/scrapercontroller.go:204 +0x12e
go.opentelemetry.io/collector/receiver/scraperhelper.(*controller).startScraping.func1(0xc00042e0e0)
go.opentelemetry.io/collector@v0.22.0/receiver/scraperhelper/scrapercontroller.go:186 +0x84
created by go.opentelemetry.io/collector/receiver/scraperhelper.(*controller).startScraping
go.opentelemetry.io/collector@v0.22.0/receiver/scraperhelper/scrapercontroller.go:175 +0x3f

What version did you use?
Version: 0.22

What config did you use?
Config:

receivers:
nginx:
endpoint: "http://localhost:44444/nginx_status"
collection_interval: 1s

processors:
batch:

exporters:
logging:
logLevel: debug

service:
pipelines:
metrics:
receivers: [nginx]
processors: [batch]
exporters: [logging]

Environment
OS: RHEL8.0
go version go1.14.12 linux/amd64, same crash with 1.16

Additional context

The nginx scraper returns an error (which is justified), but it is not caught in the calling functions. receiver/scraperhelper/scraper.go::Scrape(), then the code unconditionally calls metricCount(resourceMetrics) on a undefined resourceMetrics.

I have identified the same pattern twice in this file.

Fix
The following patch fixes the problem.

diff --git a/receiver/scraperhelper/scraper.go b/receiver/scraperhelper/scraper.go
index 06e0aa2b..2c5cb7e6 100644
--- a/receiver/scraperhelper/scraper.go
+++ b/receiver/scraperhelper/scraper.go
@@ -111,7 +111,9 @@ func (ms metricsScraper) Scrape(ctx context.Context, receiverName string) (pdata
        ctx = obsreport.ScraperContext(ctx, receiverName, ms.Name())
        ctx = obsreport.StartMetricsScrapeOp(ctx, receiverName, ms.Name())
        metrics, err := ms.ScrapeMetrics(ctx)
-       obsreport.EndMetricsScrapeOp(ctx, metrics.Len(), err)
+       if err == nil {
+               obsreport.EndMetricsScrapeOp(ctx, metrics.Len(), err)
+       }
        return metrics, err
 }

@@ -150,7 +152,9 @@ func (rms resourceMetricsScraper) Scrape(ctx context.Context, receiverName strin
        ctx = obsreport.ScraperContext(ctx, receiverName, rms.Name())
        ctx = obsreport.StartMetricsScrapeOp(ctx, receiverName, rms.Name())
        resourceMetrics, err := rms.ScrapeResourceMetrics(ctx)
-       obsreport.EndMetricsScrapeOp(ctx, metricCount(resourceMetrics), err)
+       if err == nil {
+               obsreport.EndMetricsScrapeOp(ctx, metricCount(resourceMetrics), err)
+       }
        return resourceMetrics, err
 }

[bogdandrutu]

@iror00 please open a PR :), I would not avoid calling the obsreport func, but fix calculation of the len, and pass 0 when error happend that did not produce any metric.

[codeboten]

Fixed by #2902