selftests/bpf: Test packet range of pointers sharing an idgrafted

Add tests where two packet pointers share an id and tightening one
pointer's umax from its var_off would put it less than their constant
distance from the other's umax: with an index & 0x38 capped at 50, the
base pointer keeps umax 50, so the pointer 8 bytes further on must keep
umax 58, even though its known bits allow at most 56.

These refused a valid program or accepted an out-of-bounds access before
the fix:

- check the advanced copy, load through the base: valid, was refused;
- check the base, load the byte at base + 1 through a copy advanced by
  8: was accepted;
- check base + 4, load 4 bytes at base + 2 through base + 8: reads two
  bytes past the checked range, was accepted;
- the same as the second with data_meta pointers checked against data:
  was accepted.

These pass with and without the fix and cover nearby paths:

- subtract an unknown scalar from a checked pointer and load below it
  (the range is kept across a new id);
- reach a load through two paths whose checks cover 8 and 7 bytes after
  the loaded pointer; the second path must not be pruned by the first;
- spill a copy of a pointer, check the pointer, fill the copy and load
  one byte past the checked range: the load is refused, and the copy
  has the range of the check.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20261001145255.855630-2-alexei.starovoitov@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

1 files changed, 60 insertions, 0 deletions

diff --git a/rust/syn/drops.rs b/rust/syn/drops.rs
new file mode 100644
index 000000000..2c4ae333d
--- /dev/null
+++ b/rust/syn/drops.rs
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+use std::iter;
+use std::mem::ManuallyDrop;
+use std::ops::{Deref, DerefMut};
+use std::option;
+use std::slice;
+
+#[repr(transparent)]
+pub(crate) struct NoDrop<T: ?Sized>(ManuallyDrop<T>);
+
+impl<T> NoDrop<T> {
+    pub(crate) fn new(value: T) -> Self
+    where
+        T: TrivialDrop,
+    {
+        NoDrop(ManuallyDrop::new(value))
+    }
+}
+
+impl<T: ?Sized> Deref for NoDrop<T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<T: ?Sized> DerefMut for NoDrop<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+pub(crate) trait TrivialDrop {}
+
+impl<T> TrivialDrop for iter::Empty<T> {}
+impl<T> TrivialDrop for slice::Iter<'_, T> {}
+impl<T> TrivialDrop for slice::IterMut<'_, T> {}
+impl<T> TrivialDrop for option::IntoIter<&T> {}
+impl<T> TrivialDrop for option::IntoIter<&mut T> {}
+
+#[test]
+fn test_needs_drop() {
+    use std::mem::needs_drop;
+
+    struct NeedsDrop;
+
+    impl Drop for NeedsDrop {
+        fn drop(&mut self) {}
+    }
+
+    assert!(needs_drop::<NeedsDrop>());
+
+    // Test each of the types with a handwritten TrivialDrop impl above.
+    assert!(!needs_drop::<iter::Empty<NeedsDrop>>());
+    assert!(!needs_drop::<slice::Iter<NeedsDrop>>());
+    assert!(!needs_drop::<slice::IterMut<NeedsDrop>>());
+    assert!(!needs_drop::<option::IntoIter<&NeedsDrop>>());
+    assert!(!needs_drop::<option::IntoIter<&mut NeedsDrop>>());
+}