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Running with UBSan throws runtime error regarding bitshift #52

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DanielG opened this issue Dec 18, 2019 · 0 comments · May be fixed by #53
Open

Running with UBSan throws runtime error regarding bitshift #52

DanielG opened this issue Dec 18, 2019 · 0 comments · May be fixed by #53

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@DanielG
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DanielG commented Dec 18, 2019

When running theft with ubsan enabled (-fsanitize=undefined) I get the following error:

.src/theft_random.c:79:21: runtime error: shift exponent 64 is too large for 64-bit type 'long unsigned int'

At the mentioned source location we have:

    uint8_t shift = 0;
[...]
        uint8_t take = 64 - shift;
[...]
        t->prng.buf >>= take;

According to the C standard shifting by more than the types size is undefined behaviour:

The behavior is undefined in the following circumstances:
[...]

  • An expression is shifted by a negative number or by an amount greater than or equal
    to the width of the promoted expression (6.5.7).
DanielG added a commit to DanielG/theft that referenced this issue Dec 18, 2019
@DanielG
Fix UBSan error: Shifting 64 bit type by 64 is undefined behaviour
d4f4a02 
Shifting a type by >=sizeof(type)*8 is undefined behaviour in C. Since
t->prng.buf is overwritten on the next iteration anyways this thankfully
isn't a real bug here.

Fixes silentbicycle#52
DanielG added a commit to DanielG/theft that referenced this issue Dec 18, 2019
@DanielG
Fix UBSan error: Shifting 64 bit type by 64 is undefined behaviour
8a5b577 
Shifting a type by >=sizeof(type)*8 is undefined behaviour in C. Since
t->prng.buf is overwritten on the next iteration anyways this thankfully
isn't a real bug here.

Fixes silentbicycle#52
@DanielG DanielG linked a pull request Dec 18, 2019 that will close this issue
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Fix UBSan error: Shifting 64 bit type by 64 is undefined behaviour DanielG/theft
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@DanielG