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image/gif: decode fails with "gif: too much image data" #35503

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wodim opened this issue Nov 11, 2019 · 2 comments
Open

image/gif: decode fails with "gif: too much image data" #35503

wodim opened this issue Nov 11, 2019 · 2 comments

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@wodim
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@wodim wodim commented Nov 11, 2019

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

$ go version
go version go1.13.4 windows/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
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\User\AppData\Local\go-build
set GOENV=C:\Users\User\AppData\Roaming\go\env
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=E:\vagrant\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=c:\go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=c:\go\pkg\tool\windows_amd64
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=C:\Users\User\AppData\Local\Temp\go-build365934466=/tmp/go-build -gno-record-gcc-switches

What did you do?

I have attached a zip file with three gif images that image/gif can't open (I get the message "gif: too much image data") but that other viewers can open fine. I assume they are actually invalid but perhaps image/gif could be changed to be more forgiving?

unknown.zip

@smasher164 smasher164 changed the title image/gif: images that fail to decode with "gif: too much image data" image/gif: decode fails with "gif: too much image data" Nov 11, 2019
@smasher164
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@smasher164 smasher164 commented Nov 11, 2019

/cc @nigeltao

as referenced this issue in as/goissues Nov 12, 2019
The author provides three example images which fail to decode
with the standard library's 'image/gif' package. The underlying
cause appears to be reading the "End of Information Code" from
the LZW decoder.

The decoder returns 1 byte read instead of zero, as well as a nil
error instead of io.EOF or io.ErrUnexpectedEOF. This triggers
the errTooMuch condition.

The solution to this is to comment out the errTooMuch return,
this results in a successful decode, but also fails some of the
tests. More investigation is necessary to determine whether
this solution is sound in practice.
@as
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@as as commented Nov 12, 2019

The underlying cause appears to be reading the "End of Information Code" from the LZW decoder.

The decoder returns 1 byte read instead of 0, as well as a nil error instead of io.EOF or io.ErrUnexpectedEOF. This triggers the errTooMuch condition.

One solution to this is to comment out the errTooMuch return in the if statement, this results in a successful decode, but also fails some of the tests. More investigation is necessary to determine whether this solution is sound in practice.

return errTooMuch

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