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|
use rustc_ast::Mutability;
use rustc_hir::{Expr, ExprKind, UnOp};
use rustc_middle::ty::{self, TypeAndMut};
use rustc_span::sym;
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"
}
declare_lint_pass!(InvalidReferenceCasting => [INVALID_REFERENCE_CASTING]);
impl<'tcx> LateLintPass<'tcx> for InvalidReferenceCasting {
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 init = cx.expr_or_init(e);
let Some(ty_has_interior_mutability) = is_cast_from_const_to_mut(cx, init) else {
return;
};
let orig_cast = if init.span != e.span { Some(init.span) } else { None };
let ty_has_interior_mutability = ty_has_interior_mutability.then_some(());
cx.emit_spanned_lint(
INVALID_REFERENCE_CASTING,
expr.span,
if is_assignment {
InvalidReferenceCastingDiag::AssignToRef { orig_cast, ty_has_interior_mutability }
} else {
InvalidReferenceCastingDiag::BorrowAsMut { orig_cast, ty_has_interior_mutability }
},
);
}
}
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>,
orig_expr: &'tcx Expr<'tcx>,
) -> Option<bool> {
let mut need_check_freeze = false;
let mut e = orig_expr;
let end_ty = cx.typeck_results().node_type(orig_expr.hir_id);
// Bail out early if the end type is **not** a mutable pointer.
if !matches!(end_ty.kind(), ty::RawPtr(TypeAndMut { ty: _, mutbl: Mutability::Mut })) {
return None;
}
loop {
e = e.peel_blocks();
// <expr> as ...
e = if let ExprKind::Cast(expr, _) = e.kind {
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)
)
{
expr
// ptr::from_ref(<expr>), UnsafeCell::raw_get(<expr>) or mem::transmute<_, _>(<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 | sym::transmute)
)
{
if cx.tcx.is_diagnostic_item(sym::unsafe_cell_raw_get, def_id) {
need_check_freeze = true;
}
arg
} else {
break;
};
}
let start_ty = cx.typeck_results().node_type(e.hir_id);
if let ty::Ref(_, inner_ty, Mutability::Not) = start_ty.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.
let inner_ty_has_interior_mutability =
!inner_ty.is_freeze(cx.tcx, cx.param_env) && inner_ty.has_concrete_skeleton();
(!need_check_freeze || !inner_ty_has_interior_mutability)
.then_some(inner_ty_has_interior_mutability)
} else {
None
}
}
|
