8000 expr: gnu generates a division by zero when we don't · Issue #5576 · uutils/coreutils · GitHub
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expr: gnu generates a division by zero when we don't #5576

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sylvestre opened this issue Nov 22, 2023 · 2 comments · Fixed by #5577
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expr: gnu generates a division by zero when we don't #5576

sylvestre opened this issue Nov 22, 2023 · 2 comments · Fixed by #5577
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good first issue For newcomers! U - expr

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@sylvestre
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with GNU:

$ /usr/bin/expr  "85" "/" "983" ":" "83"
/usr/bin/expr: division by zero

With our implementation:

$ ./target/debug/coreutils expr  "85" "/" "983" ":" "83"  
42

Found by the fuzzer
@cobaweel
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I'm gonna take a look.

@cobaweel
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Seems like the problem has nothing to do with division and instead is about the regex match operator (:).

According to POSIX and the GNU manual, the regex on the right side of the operator needs to be read with an implicit ^ at the start, i.e., it should only match at the beginning of the string.

Indeed, running /usr/bin/expr abc : bc gives 0, but ./target/debug/coreutils expr abc : bc gives 2. The code does indeed seem to not prepend the ^. I'm working on a fix now.

@cobaweel cobaweel mentioned this issue Nov 23, 2023
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good first issue For newcomers! U - expr
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Fix issue 5576 (regex matching bug in expr) cobaweel/coreutils
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@cobaweel @sylvestre
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