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base64 decode error about asm HOT 3 CLOSED

segmentio commented on May 26, 2024

base64 decode error

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Comments (3)

kalamay commented on May 26, 2024

Hi @Mrs4s, thanks for sending this in. I'll take a look!

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wdvxdr1123 commented on May 26, 2024

asm/base64/base64_amd64.go

Lines 145 to 147 in 86603cd

 func (enc *Encoding) DecodeString(s string) ([]byte, error) { 

 src := *(*[]byte)(unsafe.Pointer(&s)) 

 dst := make([]byte, enc.base.DecodedLen(len(s)))

Hi @kalamay , I think this unsafe usage is not correct, because string header has only 2 field but slice header has 3 field.
I have a program using this lib and it panics in std library encoding/json randomly on a computer without avx2 feature.
with panic info:

runtime error: slice bounds out of range [:8] with capacity 4

panic({0xc5d660, 0xc0003ce0a8})
        runtime/panic.go:1038 +0x215
encoding/base64.(*Encoding).Decode(0xc0000ca580, {0xc000418000, 0x5fc7, 0x5fc7}, {0xc0008120d1, 0x7fb4, 0xc000058c00})
        encoding/base64/base64.go:483 +0x605
github.com/segmentio/asm/base64.(*Encoding).Decode(0x41259a, {0xc000418000, 0x6a34044efc013184, 0x636f727070410f01}, {0xc0008120d1, 0xb2e589b8e41701b1, 0x0})
        github.com/segmentio/[email protected]/base64/base64_amd64.go:138 +0x14d
github.com/segmentio/asm/base64.(*Encoding).DecodeString(0xc00007e370, {0xc0008120d1, 0x7fb4})
        github.com/segmentio/[email protected]/base64/base64_amd64.go:148 +0xb7

I am convinced that it is caused by the unsafe convertion which produced incorrect slice capacity.

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kalamay commented on May 26, 2024

Yep, that was this issue. I've included a few updates to some internal table handling as well, but this issue should be resolved now. I appreciate you reporting this issue to us.

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