go: image/png: panic in Decode

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What version of Go are you using (go version)?

1.8

What operating system and processor architecture are you using (go env)?

linux/amd64

What did you do?

Calling png.Decode panicked at image/png.(*decoder).readImagePass, here’s the call stack:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x97f9c8]

goroutine 52345 [running]:
image/png.(*decoder).readImagePass(0xc423806400, 0x7f91a3f47ac8, 0xc42130b6d0, 0x0, 0xc42130b600, 0x0, 0x0, 0xc422d84000, 0xc423806478)
        /usr/local/go/src/image/png/reader.go:615 +0x1028
image/png.(*decoder).decode(0xc423806400, 0x0, 0x0, 0x0, 0x0)
        /usr/local/go/src/image/png/reader.go:365 +0x621
image/png.(*decoder).parseIDAT(0xc423806400, 0x4f, 0xfdb929, 0x4)
        /usr/local/go/src/image/png/reader.go:827 +0x36
image/png.(*decoder).parseChunk(0xc423806400, 0x0, 0x0)
        /usr/local/go/src/image/png/reader.go:887 +0x45a
image/png.Decode(0x1783fe0, 0xc42675ef30, 0xfdad15, 0x1, 0xc42316f740, 0x2)
        /usr/local/go/src/image/png/reader.go:946 +0x161
(caller deducted)

Looking at image/png/reader.go:615, I think it might be because of gray was nil. gray was only initialized before on line 438, in the case of !d.useTransparent, so when d.useTransparent == true and it’s the cbG8 case, it might panic. (I’m no PNG expert so I’m not sure whether that’s a case that’s not supposed to happen)

What did you expect to see?

What did you see instead?