Auto merge of #9247 - clubby789:raw_slice_pointer_cast, r=Alexendoo

New lint: Raw slice pointer cast

Adds a lint to check for a raw slice being created and cast back to a pointer, suggesting `ptr::slice_from_raw_parts`, to identify UB such as https://github.com/SimonSapin/rust-typed-arena/pull/54.
```
changelog: [`cast_slice_from_raw_parts`]: Add lint to check for `slice::from_raw_parts(.., ..) as *const _`
```

CHANGELOG.md

@@ -3627,6 +3627,7 @@ Released 2018-09-13
 [`cast_ref_to_mut`]: https://rust-lang.github.io/rust-clippy/master/index.html#cast_ref_to_mut
 [`cast_sign_loss`]: https://rust-lang.github.io/rust-clippy/master/index.html#cast_sign_loss
 [`cast_slice_different_sizes`]: https://rust-lang.github.io/rust-clippy/master/index.html#cast_slice_different_sizes
+[`cast_slice_from_raw_parts`]: https://rust-lang.github.io/rust-clippy/master/index.html#cast_slice_from_raw_parts
 [`char_lit_as_u8`]: https://rust-lang.github.io/rust-clippy/master/index.html#char_lit_as_u8
 [`chars_last_cmp`]: https://rust-lang.github.io/rust-clippy/master/index.html#chars_last_cmp
 [`chars_next_cmp`]: https://rust-lang.github.io/rust-clippy/master/index.html#chars_next_cmp

clippy_lints/src/casts/cast_slice_from_raw_parts.rs

@@ -0,0 +1,63 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::{match_def_path, meets_msrv, msrvs, paths};
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir::{def_id::DefId, Expr, ExprKind};
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, Ty};
+use rustc_semver::RustcVersion;
+
+use super::CAST_SLICE_FROM_RAW_PARTS;
+
+enum RawPartsKind {
+    Immutable,
+    Mutable,
+}
+
+fn raw_parts_kind(cx: &LateContext<'_>, did: DefId) -> Option<RawPartsKind> {
+    if match_def_path(cx, did, &paths::SLICE_FROM_RAW_PARTS) {
+        Some(RawPartsKind::Immutable)
+    } else if match_def_path(cx, did, &paths::SLICE_FROM_RAW_PARTS_MUT) {
+        Some(RawPartsKind::Mutable)
+    } else {
+        None
+    }
+}
+
+pub(super) fn check(
+    cx: &LateContext<'_>,
+    expr: &Expr<'_>,
+    cast_expr: &Expr<'_>,
+    cast_to: Ty<'_>,
+    msrv: Option<RustcVersion>,
+) {
+    if_chain! {
+        if meets_msrv(msrv, msrvs::PTR_SLICE_RAW_PARTS);
+        if let ty::RawPtr(ptrty) = cast_to.kind();
+        if let ty::Slice(_) = ptrty.ty.kind();
+        if let ExprKind::Call(fun, [ptr_arg, len_arg]) = cast_expr.peel_blocks().kind;
+        if let ExprKind::Path(ref qpath) = fun.kind;
+        if let Some(fun_def_id) = cx.qpath_res(qpath, fun.hir_id).opt_def_id();
+        if let Some(rpk) = raw_parts_kind(cx, fun_def_id);
+        then {
+            let func = match rpk {
+                RawPartsKind::Immutable => "from_raw_parts",
+                RawPartsKind::Mutable => "from_raw_parts_mut"
+            };
+            let span = expr.span;
+            let mut applicability = Applicability::MachineApplicable;
+            let ptr = snippet_with_applicability(cx, ptr_arg.span, "ptr", &mut applicability);
+            let len = snippet_with_applicability(cx, len_arg.span, "len", &mut applicability);
+            span_lint_and_sugg(
+                cx,
+                CAST_SLICE_FROM_RAW_PARTS,
+                span,
+                &format!("casting the result of `{func}` to {cast_to}"),
+                "replace with",
+                format!("core::ptr::slice_{func}({ptr}, {len})"),
+                applicability
+            );
+        }
+    }
+}

clippy_lints/src/casts/mod.rs

@@ -10,6 +10,7 @@ mod cast_ptr_alignment;
 mod cast_ref_to_mut;
 mod cast_sign_loss;
 mod cast_slice_different_sizes;
+mod cast_slice_from_raw_parts;
 mod char_lit_as_u8;
 mod fn_to_numeric_cast;
 mod fn_to_numeric_cast_any;
@@ -568,6 +569,32 @@ declare_clippy_lint! {
     pedantic,
     "borrowing just to cast to a raw pointer"
 }
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for a raw slice being cast to a slice pointer
+    ///
+    /// ### Why is this bad?
+    /// This can result in multiple `&mut` references to the same location when only a pointer is
+    /// required.
+    /// `ptr::slice_from_raw_parts` is a safe alternative that doesn't require
+    /// the same [safety requirements] to be upheld.
+    ///
+    /// ### Example
+    /// ```rust,ignore
+    /// let _: *const [u8] = std::slice::from_raw_parts(ptr, len) as *const _;
+    /// let _: *mut [u8] = std::slice::from_raw_parts_mut(ptr, len) as *mut _;
+    /// ```
+    /// Use instead:
+    /// ```rust,ignore
+    /// let _: *const [u8] = std::ptr::slice_from_raw_parts(ptr, len);
+    /// let _: *mut [u8] = std::ptr::slice_from_raw_parts_mut(ptr, len);
+    /// ```
+    /// [safety requirements]: https://doc.rust-lang.org/std/slice/fn.from_raw_parts.html#safety
+    #[clippy::version = "1.64.0"]
+    pub CAST_SLICE_FROM_RAW_PARTS,
+    suspicious,
+    "casting a slice created from a pointer and length to a slice pointer"
+}
 
 pub struct Casts {
     msrv: Option<RustcVersion>,
@@ -600,6 +627,7 @@ impl_lint_pass!(Casts => [
     CAST_ABS_TO_UNSIGNED,
     AS_UNDERSCORE,
     BORROW_AS_PTR,
+    CAST_SLICE_FROM_RAW_PARTS
 ]);
 
 impl<'tcx> LateLintPass<'tcx> for Casts {
@@ -624,7 +652,7 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
             if unnecessary_cast::check(cx, expr, cast_expr, cast_from, cast_to) {
                 return;
             }
-
+            cast_slice_from_raw_parts::check(cx, expr, cast_expr, cast_to, self.msrv);
             fn_to_numeric_cast_any::check(cx, expr, cast_expr, cast_from, cast_to);
             fn_to_numeric_cast::check(cx, expr, cast_expr, cast_from, cast_to);
             fn_to_numeric_cast_with_truncation::check(cx, expr, cast_expr, cast_from, cast_to);

clippy_lints/src/lib.register_all.rs

@@ -25,6 +25,7 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(casts::CAST_ENUM_TRUNCATION),
     LintId::of(casts::CAST_REF_TO_MUT),
     LintId::of(casts::CAST_SLICE_DIFFERENT_SIZES),
+    LintId::of(casts::CAST_SLICE_FROM_RAW_PARTS),
     LintId::of(casts::CHAR_LIT_AS_U8),
     LintId::of(casts::FN_TO_NUMERIC_CAST),
     LintId::of(casts::FN_TO_NUMERIC_CAST_WITH_TRUNCATION),

clippy_lints/src/lib.register_lints.rs

@@ -77,6 +77,7 @@ store.register_lints(&[
     casts::CAST_REF_TO_MUT,
     casts::CAST_SIGN_LOSS,
     casts::CAST_SLICE_DIFFERENT_SIZES,
+    casts::CAST_SLICE_FROM_RAW_PARTS,
     casts::CHAR_LIT_AS_U8,
     casts::FN_TO_NUMERIC_CAST,
     casts::FN_TO_NUMERIC_CAST_ANY,

clippy_lints/src/lib.register_suspicious.rs

@@ -11,6 +11,7 @@ store.register_group(true, "clippy::suspicious", Some("clippy_suspicious"), vec!
     LintId::of(casts::CAST_ABS_TO_UNSIGNED),
     LintId::of(casts::CAST_ENUM_CONSTRUCTOR),
     LintId::of(casts::CAST_ENUM_TRUNCATION),
+    LintId::of(casts::CAST_SLICE_FROM_RAW_PARTS),
     LintId::of(crate_in_macro_def::CRATE_IN_MACRO_DEF),
     LintId::of(drop_forget_ref::DROP_NON_DROP),
     LintId::of(drop_forget_ref::FORGET_NON_DROP),

tests/ui/cast_raw_slice_pointer_cast.fixed

@@ -0,0 +1,24 @@
+// run-rustfix
+#![warn(clippy::cast_slice_from_raw_parts)]
+
+#[allow(unused_imports, unused_unsafe)]
+fn main() {
+    let mut vec = vec![0u8; 1];
+    let ptr: *const u8 = vec.as_ptr();
+    let mptr = vec.as_mut_ptr();
+    let _: *const [u8] = unsafe { core::ptr::slice_from_raw_parts(ptr, 1) };
+    let _: *const [u8] = unsafe { core::ptr::slice_from_raw_parts_mut(mptr, 1) };
+    let _: *const [u8] = core::ptr::slice_from_raw_parts(ptr, 1);
+    {
+        use core::slice;
+        let _: *const [u8] = core::ptr::slice_from_raw_parts(ptr, 1);
+        use slice as one;
+        let _: *const [u8] = core::ptr::slice_from_raw_parts(ptr, 1);
+    }
+    {
+        use std::slice;
+        let _: *const [u8] = core::ptr::slice_from_raw_parts(ptr, 1);
+        use slice as one;
+        let _: *const [u8] = core::ptr::slice_from_raw_parts(ptr, 1);
+    }
+}

tests/ui/cast_raw_slice_pointer_cast.rs

@@ -0,0 +1,24 @@
+// run-rustfix
+#![warn(clippy::cast_slice_from_raw_parts)]
+
+#[allow(unused_imports, unused_unsafe)]
+fn main() {
+    let mut vec = vec![0u8; 1];
+    let ptr: *const u8 = vec.as_ptr();
+    let mptr = vec.as_mut_ptr();
+    let _: *const [u8] = unsafe { std::slice::from_raw_parts(ptr, 1) as *const [u8] };
+    let _: *const [u8] = unsafe { std::slice::from_raw_parts_mut(mptr, 1) as *mut [u8] };
+    let _: *const [u8] = unsafe { std::slice::from_raw_parts(ptr, 1) } as *const [u8];
+    {
+        use core::slice;
+        let _: *const [u8] = unsafe { slice::from_raw_parts(ptr, 1) } as *const [u8];
+        use slice as one;
+        let _: *const [u8] = unsafe { one::from_raw_parts(ptr, 1) } as *const [u8];
+    }
+    {
+        use std::slice;
+        let _: *const [u8] = unsafe { slice::from_raw_parts(ptr, 1) } as *const [u8];
+        use slice as one;
+        let _: *const [u8] = unsafe { one::from_raw_parts(ptr, 1) } as *const [u8];
+    }
+}

tests/ui/cast_raw_slice_pointer_cast.stderr

@@ -0,0 +1,46 @@
+error: casting the result of `from_raw_parts` to *const [u8]
+  --> $DIR/cast_raw_slice_pointer_cast.rs:9:35
+   |
+LL |     let _: *const [u8] = unsafe { std::slice::from_raw_parts(ptr, 1) as *const [u8] };
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `core::ptr::slice_from_raw_parts(ptr, 1)`
+   |
+   = note: `-D clippy::cast-slice-from-raw-parts` implied by `-D warnings`
+
+error: casting the result of `from_raw_parts_mut` to *mut [u8]
+  --> $DIR/cast_raw_slice_pointer_cast.rs:10:35
+   |
+LL |     let _: *const [u8] = unsafe { std::slice::from_raw_parts_mut(mptr, 1) as *mut [u8] };
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `core::ptr::slice_from_raw_parts_mut(mptr, 1)`
+
+error: casting the result of `from_raw_parts` to *const [u8]
+  --> $DIR/cast_raw_slice_pointer_cast.rs:11:26
+   |
+LL |     let _: *const [u8] = unsafe { std::slice::from_raw_parts(ptr, 1) } as *const [u8];
+   |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `core::ptr::slice_from_raw_parts(ptr, 1)`
+
+error: casting the result of `from_raw_parts` to *const [u8]
+  --> $DIR/cast_raw_slice_pointer_cast.rs:14:30
+   |
+LL |         let _: *const [u8] = unsafe { slice::from_raw_parts(ptr, 1) } as *const [u8];
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `core::ptr::slice_from_raw_parts(ptr, 1)`
+
+error: casting the result of `from_raw_parts` to *const [u8]
+  --> $DIR/cast_raw_slice_pointer_cast.rs:16:30
+   |
+LL |         let _: *const [u8] = unsafe { one::from_raw_parts(ptr, 1) } as *const [u8];
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `core::ptr::slice_from_raw_parts(ptr, 1)`
+
+error: casting the result of `from_raw_parts` to *const [u8]
+  --> $DIR/cast_raw_slice_pointer_cast.rs:20:30
+   |
+LL |         let _: *const [u8] = unsafe { slice::from_raw_parts(ptr, 1) } as *const [u8];
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `core::ptr::slice_from_raw_parts(ptr, 1)`
+
+error: casting the result of `from_raw_parts` to *const [u8]
+  --> $DIR/cast_raw_slice_pointer_cast.rs:22:30
+   |
+LL |         let _: *const [u8] = unsafe { one::from_raw_parts(ptr, 1) } as *const [u8];
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `core::ptr::slice_from_raw_parts(ptr, 1)`
+
+error: aborting due to 7 previous errors
+