Missing error handling in the MySQL plugin leads to segmentation violation

[marieof9]

Upon start of telegraf it imminently exited with a segmentation violation.

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x999806]

goroutine 52 [running]:
panic(0xf19ae0, 0xc420012050)
	/usr/local/go/src/runtime/panic.go:500 +0x1a1
database/sql.(*Rows).Next(0x0, 0x10a6d7f)
	/usr/local/go/src/database/sql/sql.go:1752 +0x26
github.com/influxdata/telegraf/plugins/inputs/mysql.(*Mysql).gatherGlobalStatuses(0xc420421420, 0xc420266210, 0xc42026c4b0, 0x4f, 0x18dfd20, 0xc420248e10, 0x0, 0xc420466730)
	/home/ubuntu/telegraf-build/src/github.com/influxdata/telegraf/plugins/inputs/mysql/mysql.go:860 +0xf5c
github.com/influxdata/telegraf/plugins/inputs/mysql.(*Mysql).gatherServer(0xc420421420, 0xc42026c4b0, 0x4f, 0x18dfd20, 0xc420248e10, 0x0, 0x0)
	/home/ubuntu/telegraf-build/src/github.com/influxdata/telegraf/plugins/inputs/mysql/mysql.go:550 +0x155
github.com/influxdata/telegraf/plugins/inputs/mysql.(*Mysql).Gather.func1(0xc4200fb950, 0xc420114068, 0xc420421420, 0x18dfd20, 0xc420248e10, 0xc420053771, 0x44)
	/home/ubuntu/telegraf-build/src/github.com/influxdata/telegraf/plugins/inputs/mysql/mysql.go:138 +0x89
created by github.com/influxdata/telegraf/plugins/inputs/mysql.(*Mysql).Gather
	/home/ubuntu/telegraf-build/src/github.com/influxdata/telegraf/plugins/inputs/mysql/mysql.go:139 +0x19a

The behaviour was triggered through miss configured file system permission. The query used to gather connection metrics from process list would simply return an error instead of a result.

mysql> SELECT user, sum(1) FROM INFORMATION_SCHEMA.PROCESSLIST GROUP BY user;
ERROR 1 (HY000): Can't create/write to file '/tmp/#sql_418_0.MYI' (Errcode: 13 - Permission denied)

For the SHOW GLOBAL STATUS query there is an error detection after the query. However for the
GatherProcessList and GatherUserStatistics this is missing and the non existent rows are iterated directly leading to a crash.

Version Information

• Telegraf v1.1.1 (git: release-1.1.0 94de9dc)
• Ubuntu 14.04.5 LTS

[sparrc]

thanks for the report! will get this fixed for version 1.3.

if anyone else hits this, the workaround is to disable gather_process_list & gather_user_statistics