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Prevent repeat slice length overflow #9819

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alamb merged 1 commit into from
Apr 25, 2026
+22 −1
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Prevent repeat slice length overflow #9819

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23 changes: 22 additions & 1 deletion arrow-buffer/src/buffer/mutable.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -284,9 +284,15 @@ impl MutableBuffer {
}

let bytes_to_repeat = size_of_val(slice_to_repeat);
let repeated_bytes = repeat_count
.checked_mul(bytes_to_repeat)
.expect("repeated slice byte length overflow");
self.len
.checked_add(repeated_bytes)
.expect("mutable buffer length overflow");
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@scovich scovich Apr 27, 2026

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I don't love introducing panics (tho clearly that's better than UB).

Any possibility to make this API more robust?

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@alamb alamb Apr 27, 2026

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I think it would be fine to add another function like try_repeat_slice_n_times... that returned a Result for those that wanted it


// Ensure capacity
self.reserve(repeat_count * bytes_to_repeat);
self.reserve(repeated_bytes);

// Save the length before we do all the copies to know where to start from
let length_before = self.len;
Expand Down Expand Up @@ -1474,6 +1480,21 @@ mod tests {
test_repeat_count(0, &[1i32, 2, 3]);
}

#[test]
#[should_panic(expected = "repeated slice byte length overflow")]
fn test_repeat_slice_count_multiply_overflow() {
let mut buffer = MutableBuffer::new(0);
buffer.repeat_slice_n_times(&[0_u64], usize::MAX / mem::size_of::<u64>() + 1);
}

#[test]
#[should_panic(expected = "mutable buffer length overflow")]
fn test_repeat_slice_count_len_overflow() {
let mut buffer = MutableBuffer::new(0);
buffer.push(0_u8);
buffer.repeat_slice_n_times(&[0_u8], usize::MAX);
}

#[test]
fn test_small_repeats_counts() {
// test any special implementation for small repeat counts
Expand Down
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