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x/crypto/bn256: TestG1Marshal fails with Go tip #25199

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mundaym opened this issue May 1, 2018 · 5 comments
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x/crypto/bn256: TestG1Marshal fails with Go tip #25199

mundaym opened this issue May 1, 2018 · 5 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done. release-blocker
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Go1.11

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@mundaym
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mundaym commented May 1, 2018

This package calls math/big.ModInverse and does not check that the result is non-nil, which appears to result in a segmentation fault when it is tested against Go tip.

See https://storage.googleapis.com/go-build-log/9ecf899b/freebsd-amd64-11_1_a2ef6f73.log for an example.
@gopherbot gopherbot added this to the Unreleased milestone May 1, 2018
@mundaym mundaym added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label May 1, 2018
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mundaym commented May 1, 2018

Presumably a result of CL 108996.

cc @bmkessler @griesemer @FiloSottile

@bradfitz bradfitz modified the milestones: Unreleased, Go1.11 May 1, 2018
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bradfitz commented May 1, 2018

Presumably a result of CL 108996.

Yes, it was CL 108996.

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diff --git a/bn256/curve.go b/bn256/curve.go
index 55b7063..9b8ff23 100644
--- a/bn256/curve.go
+++ b/bn256/curve.go
@@ -251,6 +251,9 @@ func (c *curvePoint) MakeAffine(pool *bnPool) *curvePoint {
        }
 
        zInv := pool.Get().ModInverse(c.z, p)
+       if zInv == nil {
+               zInv = pool.Get()
+       }
        t := pool.Get().Mul(c.y, zInv)
        t.Mod(t, p)
        zInv2 := pool.Get().Mul(zInv, zInv)

essentially restores the old behavior and makes the test pass. But I don't know if this is the correct fix. (If the ModInverse does not exist, in the past the returned value was undefined/the behavior of ModInverse was not specified.)

@agl ?

@griesemer griesemer added NeedsFix The path to resolution is known, but the work has not been done. and removed NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels May 1, 2018
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Change https://golang.org/cl/110695 mentions this issue: bn256: skip converting to affine coordinates for ∞

@FiloSottile FiloSottile assigned FiloSottile and unassigned agl May 1, 2018
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I honestly have no idea how it used to work. I think it relied on the fact that pool.Get() was returning 0, and that ModInverse was returning 0 as well.

@gopherbot gopherbot mentioned this issue May 2, 2018
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@FiloSottile FiloSottile mentioned this issue Jun 29, 2018
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@golang golang locked and limited conversation to collaborators May 2, 2019
c-expert-zigbee pushed a commit to c-expert-zigbee/crypto_go that referenced this issue Mar 28, 2022
@FiloSottile
bn256: explicitly fix MakeAffine for ∞
ed5ca68 
When c = ∞, z = 0 and 0 does not have a modular inverse, triggering
undefined behavior (recently changed to returning nil) in ModInverse.

Unclear how this used to work anyway. Looks like ModInverse was
leaving the receiver untouched, making zInv = 0 when pool = nil.

Fixes golang/go#25199

Change-Id: Ib39abf59f0e71cf43cdb5836142ebdd3b206fb3f
Reviewed-on: https://go-review.googlesource.com/110695
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>
c-expert-zigbee added a commit to c-expert-zigbee/crypto_go that referenced this issue Mar 29, 2022
@c-expert-zigbee
bn256: explicitly fix MakeAffine for ∞
8e7f0c7 
When c = ∞, z = 0 and 0 does not have a modular inverse, triggering
undefined behavior (recently changed to returning nil) in ModInverse.

Unclear how this used to work anyway. Looks like ModInverse was
leaving the receiver untouched, making zInv = 0 when pool = nil.

Fixes golang/go#25199

Change-Id: Ib39abf59f0e71cf43cdb5836142ebdd3b206fb3f
Reviewed-on: https://go-review.googlesource.com/110695
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>
c-expert-zigbee added a commit to c-expert-zigbee/crypto_go that referenced this issue Mar 29, 2022
@c-expert-zigbee
bn256: explicitly fix MakeAffine for ∞
2fda71e 
When c = ∞, z = 0 and 0 does not have a modular inverse, triggering
undefined behavior (recently changed to returning nil) in ModInverse.

Unclear how this used to work anyway. Looks like ModInverse was
leaving the receiver untouched, making zInv = 0 when pool = nil.

Fixes golang/go#25199

Change-Id: Ib39abf59f0e71cf43cdb5836142ebdd3b206fb3f
Reviewed-on: https://go-review.googlesource.com/110695
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>
LewiGoddard pushed a commit to LewiGoddard/crypto that referenced this issue Feb 16, 2023
@FiloSottile
bn256: explicitly fix MakeAffine for ∞
e50c3e1 
When c = ∞, z = 0 and 0 does not have a modular inverse, triggering
undefined behavior (recently changed to returning nil) in ModInverse.

Unclear how this used to work anyway. Looks like ModInverse was
leaving the receiver untouched, making zInv = 0 when pool = nil.

Fixes golang/go#25199

Change-Id: Ib39abf59f0e71cf43cdb5836142ebdd3b206fb3f
Reviewed-on: https://go-review.googlesource.com/110695
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>
BiiChris pushed a commit to BiiChris/crypto that referenced this issue Sep 15, 2023
@FiloSottile
bn256: explicitly fix MakeAffine for ∞
6e92842 
When c = ∞, z = 0 and 0 does not have a modular inverse, triggering
undefined behavior (recently changed to returning nil) in ModInverse.

Unclear how this used to work anyway. Looks like ModInverse was
leaving the receiver untouched, making zInv = 0 when pool = nil.

Fixes golang/go#25199

Change-Id: Ib39abf59f0e71cf43cdb5836142ebdd3b206fb3f
Reviewed-on: https://go-review.googlesource.com/110695
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>
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