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|
use rustc_ast::Mutability;
use rustc_data_structures::fx::FxHashMap;
use rustc_hir::{def::Res, Expr, ExprKind, HirId, Local, QPath, StmtKind, UnOp};
use rustc_middle::ty::{self, TypeAndMut};
use rustc_span::{sym, Span};
use crate::{lints::InvalidReferenceCastingDiag, LateContext, LateLintPass, LintContext};
declare_lint! {
/// The `invalid_reference_casting` lint checks for casts of `&T` to `&mut T`
/// without using interior mutability.
///
/// ### Example
///
/// ```rust,compile_fail
/// fn x(r: &i32) {
/// unsafe {
/// *(r as *const i32 as *mut i32) += 1;
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Casting `&T` to `&mut T` without using interior mutability is undefined behavior,
/// as it's a violation of Rust reference aliasing requirements.
///
/// `UnsafeCell` is the only way to obtain aliasable data that is considered
/// mutable.
INVALID_REFERENCE_CASTING,
Deny,
"casts of `&T` to `&mut T` without interior mutability"
}
#[derive(Default)]
pub struct InvalidReferenceCasting {
casted: FxHashMap<HirId, Span>,
}
impl_lint_pass!(InvalidReferenceCasting => [INVALID_REFERENCE_CASTING]);
impl<'tcx> LateLintPass<'tcx> for InvalidReferenceCasting {
fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx rustc_hir::Stmt<'tcx>) {
let StmtKind::Local(local) = stmt.kind else {
return;
};
let Local { init: Some(init), els: None, .. } = local else {
return;
};
if is_cast_from_const_to_mut(cx, init) {
self.casted.insert(local.pat.hir_id, init.span);
}
}
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
let Some((is_assignment, e)) = is_operation_we_care_about(cx, expr) else {
return;
};
let orig_cast = if is_cast_from_const_to_mut(cx, e) {
None
} else if let ExprKind::Path(QPath::Resolved(_, path)) = e.kind
&& let Res::Local(hir_id) = &path.res
&& let Some(orig_cast) = self.casted.get(hir_id) {
Some(*orig_cast)
} else {
return;
};
cx.emit_spanned_lint(
INVALID_REFERENCE_CASTING,
expr.span,
if is_assignment {
InvalidReferenceCastingDiag::AssignToRef { orig_cast }
} else {
InvalidReferenceCastingDiag::BorrowAsMut { orig_cast }
},
);
}
}
fn is_operation_we_care_about<'tcx>(
cx: &LateContext<'tcx>,
e: &'tcx Expr<'tcx>,
) -> Option<(bool, &'tcx Expr<'tcx>)> {
fn deref_assign_or_addr_of<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<(bool, &'tcx Expr<'tcx>)> {
// &mut <expr>
let inner = if let ExprKind::AddrOf(_, Mutability::Mut, expr) = expr.kind {
expr
// <expr> = ...
} else if let ExprKind::Assign(expr, _, _) = expr.kind {
expr
// <expr> += ...
} else if let ExprKind::AssignOp(_, expr, _) = expr.kind {
expr
} else {
return None;
};
if let ExprKind::Unary(UnOp::Deref, e) = &inner.kind {
Some((!matches!(expr.kind, ExprKind::AddrOf(..)), e))
} else {
None
}
}
fn ptr_write<'tcx>(
cx: &LateContext<'tcx>,
e: &'tcx Expr<'tcx>,
) -> Option<(bool, &'tcx Expr<'tcx>)> {
if let ExprKind::Call(path, [arg_ptr, _arg_val]) = e.kind
&& let ExprKind::Path(ref qpath) = path.kind
&& let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
&& matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::ptr_write | sym::ptr_write_volatile | sym::ptr_write_unaligned))
{
Some((true, arg_ptr))
} else {
None
}
}
deref_assign_or_addr_of(e).or_else(|| ptr_write(cx, e))
}
fn is_cast_from_const_to_mut<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'tcx>) -> bool {
let e = e.peel_blocks();
fn from_casts<'tcx>(
cx: &LateContext<'tcx>,
e: &'tcx Expr<'tcx>,
need_check_freeze: &mut bool,
) -> Option<&'tcx Expr<'tcx>> {
// <expr> as *mut ...
let mut e = if let ExprKind::Cast(e, t) = e.kind
&& let ty::RawPtr(TypeAndMut { mutbl: Mutability::Mut, .. }) = cx.typeck_results().node_type(t.hir_id).kind() {
e
// <expr>.cast_mut()
} else if let ExprKind::MethodCall(_, expr, [], _) = e.kind
&& let Some(def_id) = cx.typeck_results().type_dependent_def_id(e.hir_id)
&& cx.tcx.is_diagnostic_item(sym::ptr_cast_mut, def_id) {
expr
// UnsafeCell::raw_get(<expr>)
} else if let ExprKind::Call(path, [arg]) = e.kind
&& let ExprKind::Path(ref qpath) = path.kind
&& let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
&& cx.tcx.is_diagnostic_item(sym::unsafe_cell_raw_get, def_id)
{
*need_check_freeze = true;
arg
} else {
return None;
};
let mut had_at_least_one_cast = false;
loop {
e = e.peel_blocks();
// <expr> as *mut/const ... or <expr> as <uint>
e = if let ExprKind::Cast(expr, t) = e.kind
&& matches!(cx.typeck_results().node_type(t.hir_id).kind(), ty::RawPtr(_) | ty::Uint(_)) {
had_at_least_one_cast = true;
expr
// <expr>.cast(), <expr>.cast_mut() or <expr>.cast_const()
} else if let ExprKind::MethodCall(_, expr, [], _) = e.kind
&& let Some(def_id) = cx.typeck_results().type_dependent_def_id(e.hir_id)
&& matches!(
cx.tcx.get_diagnostic_name(def_id),
Some(sym::ptr_cast | sym::const_ptr_cast | sym::ptr_cast_mut | sym::ptr_cast_const)
)
{
had_at_least_one_cast = true;
expr
// ptr::from_ref(<expr>) or UnsafeCell::raw_get(<expr>)
} else if let ExprKind::Call(path, [arg]) = e.kind
&& let ExprKind::Path(ref qpath) = path.kind
&& let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
&& matches!(
cx.tcx.get_diagnostic_name(def_id),
Some(sym::ptr_from_ref | sym::unsafe_cell_raw_get)
)
{
if cx.tcx.is_diagnostic_item(sym::unsafe_cell_raw_get, def_id) {
*need_check_freeze = true;
}
return Some(arg);
} else if had_at_least_one_cast {
return Some(e);
} else {
return None;
};
}
}
fn from_transmute<'tcx>(
cx: &LateContext<'tcx>,
e: &'tcx Expr<'tcx>,
) -> Option<&'tcx Expr<'tcx>> {
// mem::transmute::<_, *mut _>(<expr>)
if let ExprKind::Call(path, [arg]) = e.kind
&& let ExprKind::Path(ref qpath) = path.kind
&& let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
&& cx.tcx.is_diagnostic_item(sym::transmute, def_id)
&& let ty::RawPtr(TypeAndMut { mutbl: Mutability::Mut, .. }) = cx.typeck_results().node_type(e.hir_id).kind() {
Some(arg)
} else {
None
}
}
let mut need_check_freeze = false;
let Some(e) = from_casts(cx, e, &mut need_check_freeze).or_else(|| from_transmute(cx, e))
else {
return false;
};
let e = e.peel_blocks();
let node_type = cx.typeck_results().node_type(e.hir_id);
if let ty::Ref(_, inner_ty, Mutability::Not) = node_type.kind() {
// If an UnsafeCell method is involved we need to additionaly check the
// inner type for the presence of the Freeze trait (ie does NOT contain
// an UnsafeCell), since in that case we would incorrectly lint on valid casts.
//
// We also consider non concrete skeleton types (ie generics)
// to be an issue since there is no way to make it safe for abitrary types.
!need_check_freeze
|| inner_ty.is_freeze(cx.tcx, cx.param_env)
|| !inner_ty.has_concrete_skeleton()
} else {
false
}
}
|
