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encoding/json: Inconsistent results with pointers and duplicated keys #31776

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elwinar opened this issue May 1, 2019 · 2 comments

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@elwinar
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commented May 1, 2019

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

$ go version
go version go1.12.4 linux/amd64

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
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/elwinar/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/elwinar/.go"
GOPROXY=""
GORACE=""
GOROOT="/usr/lib/go"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build786320136=/tmp/go-build -gno-record-gcc-switches"

What did you do?

https://play.golang.org/p/8ELiG37J-JI

What did you expect to see?

{<nil>} <nil>
{<nil>} <nil>

What did you see instead?

{0x40c1e8} <nil>
{<nil>} <nil>

As mentioned is dvyukov/go-fuzz-corpus#3, although the result itself is valid stricto sensu, it is inconsistent. We would expect either the first or the last indirection to be always nil, while it seems to depends on the previous value of the field.

@elwinar

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commented May 1, 2019

@gopherbot

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commented May 1, 2019

Change https://golang.org/cl/174699 mentions this issue: encoding/json: check the type of a value when indirecting it

@katiehockman katiehockman added this to the Go1.14 milestone May 1, 2019

elwinar pushed a commit to elwinar/go that referenced this issue Sep 9, 2019
Romain Baugue
encoding/json: don't indirect pointers when decoding null
The indirect method checked the type of the child when indirecting a
pointer. If the current value is a pointer and we are decoding null, we
can skip this entirely and return early, avoiding the whole descent.

Fixes golang#31776

Change-Id: Ib8b2a2357572c41f56fceac59b5a858980f3f65e
elwinar added a commit to elwinar/go that referenced this issue Sep 10, 2019
encoding/json: don't indirect pointers when decoding null
The indirect method checked the type of the child when indirecting a
pointer. If the current value is a pointer and we are decoding null, we
can skip this entirely and return early, avoiding the whole descent.

Fixes golang#31776

Change-Id: Ib8b2a2357572c41f56fceac59b5a858980f3f65e

@gopherbot gopherbot closed this in b6ec56b Sep 10, 2019

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