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Use checked arithmetic for the entry index in Extents #314

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Use checked arithmetic for the entry index in Extents #314

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12 changes: 8 additions & 4 deletions src/iters/extents.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ use crate::checksum::Checksum;
use crate::error::{Corrupt, Ext4Error};
use crate::extent::Extent;
use crate::inode::{Inode, InodeIndex};
use crate::util::{read_u16le, read_u32le, u64_from_hilo};
use crate::util::{read_u16le, read_u32le, u64_from_hilo, usize_from_u32};
use crate::Ext4;
use alloc::vec;
use alloc::vec::Vec;
Expand Down Expand Up @@ -88,7 +88,7 @@ struct ToVisitItem {

// Current index within the node. 0 is the node header, 1 is the
// first entry, etc.
entry: u16,
entry: u32,

// Node depth, copied from the node header.
depth: u16,
Expand All @@ -115,7 +115,7 @@ impl ToVisitItem {
}

fn entry(&self) -> Option<&[u8]> {
let start = usize::from(self.entry) * ENTRY_SIZE_IN_BYTES;
let start = usize_from_u32(self.entry) * ENTRY_SIZE_IN_BYTES;
self.node.get(start..start + ENTRY_SIZE_IN_BYTES)
}
}
Expand Down Expand Up @@ -167,7 +167,11 @@ impl Extents {
// Increment at the start to ensure that early returns don't
// accidentally skip the increment. Since entry 0 is the node
// header, entry 1 is the first actual node entry.
item.entry += 1;
//
// OK to unwrap: there are at most `2^16-1` entries, plus 1 for
// the header. Adding 1 here brings the maximum value to
// `2^16+1`. This fits in `item.entry` since it is a `u32`.
item.entry = item.entry.checked_add(1).unwrap();

let Some(entry) = &item.entry() else {
// Reached end of this node.
Expand Down