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