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Cap count twice

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This commit is contained in:
Christian Poveda
2019-11-13 11:57:20 -05:00
parent 6e37f2f3e1
commit edd0157069
1 changed files with 12 additions and 2 deletions
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src/shims/fs.rs
+12 -2
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@@ -168,10 +168,13 @@ fn read(
let ptr_size = this.pointer_size().bits();
// We cap the number of read bytes to the largest value that we are able to fit in both the
// host's and target's `isize`.
let count = this
.read_scalar(count_op)?
.to_machine_usize(&*this.tcx)?
.min(1 << (ptr_size - 1));
.min(1 << (ptr_size - 1))
.min(isize::max_value() as u64);
// Reading zero bytes should not change `buf`.
if count == 0 {
return Ok(0);
@@ -180,6 +183,8 @@ fn read(
let buf = this.read_scalar(buf_op)?.not_undef()?;
if let Some(handle) = this.machine.file_handler.handles.get_mut(&fd) {
// This can never fail because `count` was capped to be smaller than
// `isize::max_value()`.
let count = isize::try_from(count).unwrap();
// We want to read at most `count` bytes. We are sure that `count` is not negative
// because it was a target's `usize`. Also we are sure that its smaller than
@@ -188,6 +193,8 @@ fn read(
let result = handle
.file
.read(&mut bytes)
// `File::read` never returns a value larger than `i64::max_value()`, so this
// unwrap cannot fail.
.map(|c| i64::try_from(c).unwrap());
match result {
@@ -218,10 +225,13 @@ fn write(
let ptr_size = this.pointer_size().bits();
// We cap the number of read bytes to the largest value that we are able to fit in both the
// host's and target's `isize`.
let count = this
.read_scalar(count_op)?
.to_machine_usize(&*this.tcx)?
.min(1 << (ptr_size - 1));
.min(1 << (ptr_size - 1))
.min(isize::max_value() as u64);
// Writing zero bytes should not change `buf`.
if count == 0 {
return Ok(0);