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Auto merge of #116070 - eduardosm:IoSlice-advance_slices-checked_add, r=Mark-Simulacrum

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Avoid overflow in `IoSlice::advance_slices`

Noticed in https://github.com/rust-lang/rust/issues/62726#issuecomment-1713997431.
This commit is contained in:
bors 2023-09-25 18:29:26 +00:00
commit 7bf47a4792
1 changed files with 19 additions and 16 deletions
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35
library/std/src/io/mod.rs
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@ -1236,22 +1236,22 @@ impl<'a> IoSliceMut<'a> {
pub fn advance_slices(bufs: &mut &mut [IoSliceMut<'a>], n: usize) {
// Number of buffers to remove.
let mut remove = 0;
// Total length of all the to be removed buffers.
let mut accumulated_len = 0;
// Remaining length before reaching n.
let mut left = n;
for buf in bufs.iter() {
if accumulated_len + buf.len() > n {
break;
} else {
accumulated_len += buf.len();
if let Some(remainder) = left.checked_sub(buf.len()) {
left = remainder;
remove += 1;
} else {
break;
}
}
*bufs = &mut take(bufs)[remove..];
if bufs.is_empty() {
assert!(n == accumulated_len, "advancing io slices beyond their length");
assert!(left == 0, "advancing io slices beyond their length");
} else {
bufs[0].advance(n - accumulated_len)
bufs[0].advance(left);
}
}
}
@ -1379,22 +1379,25 @@ impl<'a> IoSlice<'a> {
pub fn advance_slices(bufs: &mut &mut [IoSlice<'a>], n: usize) {
// Number of buffers to remove.
let mut remove = 0;
// Total length of all the to be removed buffers.
let mut accumulated_len = 0;
// Remaining length before reaching n. This prevents overflow
// that could happen if the length of slices in `bufs` were instead
// accumulated. Those slice may be aliased and, if they are large
// enough, their added length may overflow a `usize`.
let mut left = n;
for buf in bufs.iter() {
if accumulated_len + buf.len() > n {
break;
} else {
accumulated_len += buf.len();
if let Some(remainder) = left.checked_sub(buf.len()) {
left = remainder;
remove += 1;
} else {
break;
}
}
*bufs = &mut take(bufs)[remove..];
if bufs.is_empty() {
assert!(n == accumulated_len, "advancing io slices beyond their length");
assert!(left == 0, "advancing io slices beyond their length");
} else {
bufs[0].advance(n - accumulated_len)
bufs[0].advance(left);
}
}
}