math/rand: read can panic

[tcsato995]

go version go1.23.2 linux/amd64

Happened only once, so not sure how to reproduce it, however calling rand.read with a rngSource caused a panic, see stack trace below. It was called in a 3rd party library, but if that matters the buffer slice given to the read method has a hardcoded size of 56, and rand instance was created with rand.NewSource(time.Now().UnixNano())

panic: runtime error: index out of range [-1]

goroutine 138 [running]:
math/rand.(*rngSource).Uint64(...)
	/usr/local/go/src/math/rand/rng.go:249
math/rand.(*rngSource).Int63(...)
	/usr/local/go/src/math/rand/rng.go:234
math/rand.read({0xc000117680, 0x38, 0xc000df1888?}, {0x1eb34e0?, 0xc000375500?}, 0xc000364a70, 0xc000364a78)
	/usr/local/go/src/math/rand/rand.go:285 +0x185
math/rand.(*Rand).Read(0xc000bcf0e0?, {0xc000117680?, 0x7f1d0cc6c108?, 0x30?})
	/usr/local/go/src/math/rand/rand.go:275 +0x65
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[mvdan]

It looks like your program may have a data race causing memory corruption. Please try running your program with -race: https://go.dev/doc/articles/race_detector

[gabyhelp]

Related Issues

• math/rand panic:runtime error: index out of range #16205 (closed)
• math/rand: document that math.Rand is not safe for concurrent use #3611 (closed)
• math/rand: Intn: panic index out of range #17629 (closed)
• rand panic #34369 (closed)
• math/rand: panic generating NormFloat64 #66086 (closed)
• math/rand: index out of range in (*rngSource).Int63 #21099 (closed)
• crypto/rand: Int panics if argument is zero #5187 (closed)
• math/rand: Calling single rand.Rand object from multiple threaded gorouttiness panics #8308 (closed)
• crypto/rand: panic in rand.Read() when called from wasm in a browser #46256 (closed)

Related Discussions

• Go 1.6: panic in math/rand/rng.go

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[tcsato995]

@mvdan

It looks like your program may have a data race causing memory corruption. Please try running your program with -race: https://go.dev/doc/articles/race_detector

Indeed, looks like it was a data race issue. Thanks for pointing me in the right direction. Closing the issue.

==================
WARNING: DATA RACE
Read at 0x00c000310ef8 by goroutine 55:
  math/rand.read()
      /usr/local/go/src/math/rand/rand.go:283 +0x53
  math/rand.(*Rand).Read()
      /usr/local/go/src/math/rand/rand.go:279 +0x144
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