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fix: kernel: ipld::read not using offset correctly. #551

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fix: kernel: ipld::read not using offset correctly. #551

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14 changes: 8 additions & 6 deletions fvm/src/kernel/default.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -364,18 +364,20 @@ where

fn block_read(&mut self, id: BlockId, offset: u32, buf: &mut [u8]) -> Result<u32> {
let data = self.blocks.get(id).or_illegal_argument()?.data();
let data_len = data.len();

let len = if offset as usize >= data.len() {
0
} else {
buf.len().min(data.len())
};
// Calculate the number of bytes we are effectively copying.
// If the offset is beyond or equal to the length of data, we copy no bytes.
// Else, we copy as many bytes as the supplied buffer will allow.
let len = (offset as usize >= data_len)
.then_some(0)
.unwrap_or_else(|| buf.len().min(data_len - offset as usize)); // can't overflow

self.call_manager
.charge_gas(self.call_manager.price_list().on_block_read(len))?;

if len != 0 {
buf.copy_from_slice(&data[offset as usize..][..len]);
buf[..len].copy_from_slice(&data[offset as usize..][..len]);
}

Ok(len as u32)
Expand Down