read: Fix subtraction overflow when Abbreviations::get is given 0
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philipc
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May 14, 2020
src/read/abbrev.rs
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| let code_usize = code as usize; | ||
| if code_usize as u64 == code && code_usize - 1 < self.vec.len() { | ||
| Some(&self.vec[code_usize - 1]) | ||
| let index = (code as usize).checked_sub(1)?; |
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Can you change this to try_into as well?
I also feel like we should simply use wrapping_sub here, but it probably doesn't matter. That would mean we might end up looking up a 0 in the map, but it would still be correct and this function should never be called with 0 anyway. Is this something you encountered, or are you just auditing arithmetic?
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Is this something you encountered, or are you just auditing arithmetic?
Encountered during fuzzing. Not that any gimli-internal debug_info look up code was doing get(0) but the fuzz target itself did.
If we don't want this to ever be called with zero, then we should probably switch it to use NonZeroU64.
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Alternatively, we could make this take
NonZeroU64instead ofu64, but those can be kind of a pain to work with.