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Allowing passing a null pointer to getrandom() when length is 0 #884

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Merged
merged 3 commits into from
Aug 4, 2019
Merged

Allowing passing a null pointer to getrandom() when length is 0 #884

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0505868
Do nothing when we try to generate random data of length 0
Aaron1011 Aug 4, 2019
c2f681f
Add semicolon
Aaron1011 Aug 4, 2019
4d3398f
Replace match with expect()
Aaron1011 Aug 4, 2019
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17 changes: 13 additions & 4 deletions src/helpers.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -81,12 +81,21 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
ptr: Scalar<Tag>,
len: usize,
) -> InterpResult<'tcx> {
// Some programs pass in a null pointer and a length of 0
// to their platform's random-generation function (e.g. getrandom())
// on Linux. For compatibility with these programs, we don't perform
// any additional checks - it's okay if the pointer is invalid,
// since we wouldn't actually be writing to it.
if len == 0 {
return Ok(());
}
let this = self.eval_context_mut();

let ptr = match this.memory().check_ptr_access(ptr, Size::from_bytes(len as u64), Align::from_bytes(1).unwrap())? {
Some(ptr) => ptr,
None => return Ok(()), // zero-sized access
};
let ptr = this.memory().check_ptr_access(
ptr,
Size::from_bytes(len as u64),
Align::from_bytes(1).unwrap()
)?.expect("we already checked for size 0");

let rng = this.memory_mut().extra.rng.get_mut();
let mut data = vec![0; len];
Expand Down