| use crate::consts::{constant_context, Constant}; |
| use crate::utils::{match_qpath, paths, span_lint}; |
| use if_chain::if_chain; |
| use rustc_ast::ast::LitKind; |
| use rustc_hir::{Expr, ExprKind}; |
| use rustc_lint::{LateContext, LateLintPass, LintContext}; |
| use rustc_middle::lint::in_external_macro; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| |
| declare_clippy_lint! { |
| /// **What it does:** Checks for transmute calls which would receive a null pointer. |
| /// |
| /// **Why is this bad?** Transmuting a null pointer is undefined behavior. |
| /// |
| /// **Known problems:** Not all cases can be detected at the moment of this writing. |
| /// For example, variables which hold a null pointer and are then fed to a `transmute` |
| /// call, aren't detectable yet. |
| /// |
| /// **Example:** |
| /// ```rust |
| /// let null_ref: &u64 = unsafe { std::mem::transmute(0 as *const u64) }; |
| /// ``` |
| pub TRANSMUTING_NULL, |
| correctness, |
| "transmutes from a null pointer to a reference, which is undefined behavior" |
| } |
| |
| declare_lint_pass!(TransmutingNull => [TRANSMUTING_NULL]); |
| |
| const LINT_MSG: &str = "transmuting a known null pointer into a reference."; |
| |
| impl<'tcx> LateLintPass<'tcx> for TransmutingNull { |
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { |
| if in_external_macro(cx.sess(), expr.span) { |
| return; |
| } |
| |
| if_chain! { |
| if let ExprKind::Call(ref func, ref args) = expr.kind; |
| if let ExprKind::Path(ref path) = func.kind; |
| if match_qpath(path, &paths::STD_MEM_TRANSMUTE); |
| if args.len() == 1; |
| |
| then { |
| |
| // Catching transmute over constants that resolve to `null`. |
| let mut const_eval_context = constant_context(cx, cx.tables()); |
| if_chain! { |
| if let ExprKind::Path(ref _qpath) = args[0].kind; |
| let x = const_eval_context.expr(&args[0]); |
| if let Some(constant) = x; |
| if let Constant::RawPtr(0) = constant; |
| then { |
| span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG) |
| } |
| } |
| |
| // Catching: |
| // `std::mem::transmute(0 as *const i32)` |
| if_chain! { |
| if let ExprKind::Cast(ref inner_expr, ref _cast_ty) = args[0].kind; |
| if let ExprKind::Lit(ref lit) = inner_expr.kind; |
| if let LitKind::Int(0, _) = lit.node; |
| then { |
| span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG) |
| } |
| } |
| |
| // Catching: |
| // `std::mem::transmute(std::ptr::null::<i32>())` |
| if_chain! { |
| if let ExprKind::Call(ref func1, ref args1) = args[0].kind; |
| if let ExprKind::Path(ref path1) = func1.kind; |
| if match_qpath(path1, &paths::STD_PTR_NULL); |
| if args1.is_empty(); |
| then { |
| span_lint(cx, TRANSMUTING_NULL, expr.span, LINT_MSG) |
| } |
| } |
| |
| // FIXME: |
| // Also catch transmutations of variables which are known nulls. |
| // To do this, MIR const propagation seems to be the better tool. |
| // Whenever MIR const prop routines are more developed, this will |
| // become available. As of this writing (25/03/19) it is not yet. |
| } |
| } |
| } |
| } |