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net: IPNet.String panics with nil receiver #50271

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Beginner18 opened this issue Dec 20, 2021 · 2 comments
Closed

net: IPNet.String panics with nil receiver #50271

Beginner18 opened this issue Dec 20, 2021 · 2 comments
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FrozenDueToAge help wanted NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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@Beginner18
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Beginner18 commented Dec 20, 2021 •
edited by seankhliao

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

1.15.5

Does this issue reproduce with the latest release?

YES

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

go env Output
$ go env

What did you do?

panic, if IPNet is nil

func (n *IPNet) String() string {
	nn, m := networkNumberAndMask(n)
	if nn == nil || m == nil {
		return "<nil>"
	}
	l := simpleMaskLength(m)
	if l == -1 {
		return nn.String() + "/" + m.String()
	}
	return nn.String() + "/" + uitoa(uint(l))
}

What did you expect to see?

IPNet.String() should not panic, even IPNet is nil

What did you see instead?

    panic(0x194abc0, 0x2156090)
        	/usr/local/go/src/runtime/panic.go:969 +0x1b9
        net.networkNumberAndMask(0x0, 0x0, 0x10, 0x23bb108, 0xc000123d30, 0xc00003ed00, 0xc000077dd0)
        	/usr/local/go/src/net/ip.go:476 +0x26
        net.(*IPNet).String(0x0, 0xc00011f470, 0x18eed80)
        	/usr/local/go/src/net/ip.go:526 +0x45
@Beginner18 Beginner18 changed the title affected/package: net/ip.go IPNet.String panic Dec 20, 2021
@ianlancetaylor ianlancetaylor changed the title net/ip.go IPNet.String panic net: IPNet.String panic Dec 20, 2021
@ianlancetaylor ianlancetaylor changed the title net: IPNet.String panic net: IPNet.String panics with nil receiver Dec 20, 2021
@ianlancetaylor ianlancetaylor added help wanted NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Dec 20, 2021
@ianlancetaylor ianlancetaylor added this to the Backlog milestone Dec 20, 2021
@ianlancetaylor
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While in general the standard library is happy to panic when invoked on an invalid value, I agree that perhaps the String method should not do so.

@gopherbot
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Change https://golang.org/cl/373075 mentions this issue: net: do not panic on nil IPNet.String()

jproberts pushed a commit to jproberts/go that referenced this issue Jun 21, 2022
@zx2c4 @jproberts
net: do not panic on nil IPNet.String()
d9c0aeb 
The code looks like it was already trying to avoid this but missed a
spot.

Fixes golang#50271.

Change-Id: I450adac3f618b9535b61a28e6a160eacc351d47c
Reviewed-on: https://go-review.googlesource.com/c/go/+/373075
Trust: Jason Donenfeld <Jason@zx2c4.com>
Run-TryBot: Jason Donenfeld <Jason@zx2c4.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
@golang golang locked and limited conversation to collaborators Jan 5, 2023
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