Creating a new logger on Linux without write permissions to /var causes panic

[timraymond]

When creating a new log.(*Logger) with NewLogger, and then subsequently initializing it with log.(*Logger).Init, a panic will result when any of the logging methods are invoked (e.g. log.(*Logger).Debugf). The resulting panic (abridged for privacy) is:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x4feb76]

goroutine 1 [running]:
log.(*Logger).Output(0xc00051e7d0, 0x13, {0xc000524b70, 0x23})
        /home/tim/goroots/go1.17/src/log/log.go:184 +0x356
log.(*Logger).Printf(0x198e233, {0xc00055e198, 0xc000511ac8}, {0xc00022d9a0, 0x2, 0x73e3a5})
        /home/tim/goroots/go1.17/src/log/log.go:191 +0x4c
github.com/Azure/azure-container-networking/log.(*Logger).logf(0xc000213810, {0x19937f5, 0xb}, {0xc00022d9a0, 0x1, 0x1})
        /home/tim/go/pkg/mod/github.com/!azure/azure-container-networking@v1.4.16/log/logger.go:204 +0xf0
github.com/Azure/azure-container-networking/log.(*Logger).Logf(0xc000213810, {0x19937f5, 0x7fa856e433a0}, {0xc00022d9a0, 0x10, 0x7fa87dc72a68})
        /home/tim/go/pkg/mod/github.com/!azure/azure-container-networking@v1.4.16/log/logger.go:210 +0x8c
github.com/Azure/azure-container-networking/log.(*Logger).Debugf(...)
        /home/tim/go/pkg/mod/github.com/!azure/azure-container-networking@v1.4.16/log/logger.go:229

The root cause of this is the nil writer being provided to the log.New invocation. If write permissions were available, this would be set properly by log.SetOutput.

I don't know if this behavior is also present on Windows since I haven't personally tested it. In an out-of-band conversation, @ramiro-gamarra mentioned that this is a Linux-specific issue with this package.