--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libpam-sys/libpam-sys-helpers/src/memory.rs	Thu Jul 03 14:28:04 2025 -0400
@@ -0,0 +1,510 @@
+//! Helpers to deal with annoying memory management in the PAM API.
+//!
+//!
+
+use std::error::Error;
+use std::marker::{PhantomData, PhantomPinned};
+use std::mem::ManuallyDrop;
+use std::ptr::NonNull;
+use std::{any, fmt, mem, slice};
+
+/// A pointer-to-pointer-to-message container for PAM's conversation callback.
+///
+/// The PAM conversation callback requires a pointer to a pointer of
+/// `pam_message`s. Linux-PAM handles this differently than all other
+/// PAM implementations (including the X/SSO PAM standard).
+///
+/// X/SSO appears to specify a pointer-to-pointer-to-array:
+///
+/// ```text
+///           points to  ┌────────────┐       ╔═ Message[] ═╗
+/// messages ┄┄┄┄┄┄┄┄┄┄> │ *messages ┄┼┄┄┄┄┄> ║ style       ║
+///                      └────────────┘       ║ data ┄┄┄┄┄┄┄╫┄┄> ...
+///                                           ╟─────────────╢
+///                                           ║ style       ║
+///                                           ║ data ┄┄┄┄┄┄┄╫┄┄> ...
+///                                           ╟─────────────╢
+///                                           ║ ...         ║
+/// ```
+///
+/// whereas Linux-PAM uses an `**argv`-style pointer-to-array-of-pointers:
+///
+/// ```text
+///           points to  ┌──────────────┐      ╔═ Message ═╗
+/// messages ┄┄┄┄┄┄┄┄┄┄> │ messages[0] ┄┼┄┄┄┄> ║ style     ║
+///                      │ messages[1] ┄┼┄┄┄╮  ║ data ┄┄┄┄┄╫┄┄> ...
+///                      │ ...          │   ┆  ╚═══════════╝
+///                                         ┆
+///                                         ┆    ╔═ Message ═╗
+///                                         ╰┄┄> ║ style     ║
+///                                              ║ data ┄┄┄┄┄╫┄┄> ...
+///                                              ╚═══════════╝
+/// ```
+///
+/// Because the `messages` remain owned by the application which calls into PAM,
+/// we can solve this with One Simple Trick: make the intermediate list point
+/// into the same array:
+///
+/// ```text
+///           points to  ┌──────────────┐      ╔═ Message[] ═╗
+/// messages ┄┄┄┄┄┄┄┄┄┄> │ messages[0] ┄┼┄┄┄┄> ║ style       ║
+///                      │ messages[1] ┄┼┄┄╮   ║ data ┄┄┄┄┄┄┄╫┄┄> ...
+///                      │ ...          │  ┆   ╟─────────────╢
+///                                        ╰┄> ║ style       ║
+///                                            ║ data ┄┄┄┄┄┄┄╫┄┄> ...
+///                                            ╟─────────────╢
+///                                            ║ ...         ║
+///
+/// ```
+#[derive(Debug)]
+pub struct PtrPtrVec<T> {
+    data: Vec<T>,
+    pointers: Vec<*const T>,
+}
+
+// Since this is a wrapper around a Vec with no dangerous functionality*,
+// this can be Send and Sync provided the original Vec is.
+//
+// * It will only become unsafe when the user dereferences a pointer or sends it
+// to an unsafe function.
+unsafe impl<T> Send for PtrPtrVec<T> where Vec<T>: Send {}
+unsafe impl<T> Sync for PtrPtrVec<T> where Vec<T>: Sync {}
+
+impl<T> PtrPtrVec<T> {
+    /// Takes ownership of the given Vec and creates a vec of pointers to it.
+    pub fn new(data: Vec<T>) -> Self {
+        let pointers: Vec<_> = data.iter().map(|r| r as *const T).collect();
+        Self { data, pointers }
+    }
+
+    /// Gives you back your Vec.
+    pub fn into_inner(self) -> Vec<T> {
+        self.data
+    }
+
+    /// Gets a pointer-to-pointer suitable for passing into the Conversation.
+    pub fn as_ptr<Dest>(&self) -> *const *const Dest {
+        Self::assert_size::<Dest>();
+        self.pointers.as_ptr().cast::<*const Dest>()
+    }
+
+    /// Iterates over a Linux-PAM–style pointer-to-array-of-pointers.
+    ///
+    /// # Safety
+    ///
+    /// `ptr_ptr` must be a valid pointer to an array of pointers,
+    /// there must be at least `count` valid pointers in the array,
+    /// and each pointer in that array must point to a valid `T`.
+    #[deprecated = "use [`Self::iter_over`] instead, unless you really need this specific version"]
+    #[allow(dead_code)]
+    pub unsafe fn iter_over_linux<'a, Src>(
+        ptr_ptr: *const *const Src,
+        count: usize,
+    ) -> impl Iterator<Item = &'a T>
+    where
+        T: 'a,
+    {
+        Self::assert_size::<Src>();
+        slice::from_raw_parts(ptr_ptr.cast::<&T>(), count)
+            .iter()
+            .copied()
+    }
+
+    /// Iterates over an X/SSO–style pointer-to-pointer-to-array.
+    ///
+    /// # Safety
+    ///
+    /// You must pass a valid pointer to a valid pointer to an array,
+    /// there must be at least `count` elements in the array,
+    /// and each value in that array must be a valid `T`.
+    #[deprecated = "use [`Self::iter_over`] instead, unless you really need this specific version"]
+    #[allow(dead_code)]
+    pub unsafe fn iter_over_xsso<'a, Src>(
+        ptr_ptr: *const *const Src,
+        count: usize,
+    ) -> impl Iterator<Item = &'a T>
+    where
+        T: 'a,
+    {
+        Self::assert_size::<Src>();
+        slice::from_raw_parts(*ptr_ptr.cast(), count).iter()
+    }
+
+    /// Iterates over a PAM message list appropriate to your system's impl.
+    ///
+    /// This selects the correct pointer/array structure to use for a message
+    /// that was given to you by your system.
+    ///
+    /// # Safety
+    ///
+    /// `ptr_ptr` must point to a valid message list, there must be at least
+    /// `count` messages in the list, and all messages must be a valid `Src`.
+    #[allow(deprecated)]
+    pub unsafe fn iter_over<'a, Src>(
+        ptr_ptr: *const *const Src,
+        count: usize,
+    ) -> impl Iterator<Item = &'a T>
+    where
+        T: 'a,
+    {
+        #[cfg(pam_impl = "LinuxPam")]
+        return Self::iter_over_linux(ptr_ptr, count);
+        #[cfg(not(pam_impl = "LinuxPam"))]
+        return Self::iter_over_xsso(ptr_ptr, count);
+    }
+
+    fn assert_size<That>() {
+        debug_assert_eq!(
+            mem::size_of::<T>(),
+            mem::size_of::<That>(),
+            "type {t} is not the size of {that}",
+            t = any::type_name::<T>(),
+            that = any::type_name::<That>(),
+        );
+    }
+}
+
+/// Error returned when attempting to allocate a buffer that is too big.
+///
+/// This is specifically used in [`OwnedBinaryPayload`] when you try to allocate
+/// a message larger than 2<sup>32</sup> bytes.
+#[derive(Debug, PartialEq)]
+pub struct TooBigError {
+    pub size: usize,
+    pub max: usize,
+}
+
+impl Error for TooBigError {}
+
+impl fmt::Display for TooBigError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            f,
+            "can't allocate a message of {size} bytes (max {max})",
+            size = self.size,
+            max = self.max
+        )
+    }
+}
+
+/// A trait wrapping memory management.
+///
+/// This is intended to allow you to bring your own allocator for
+/// [`OwnedBinaryPayload`]s.
+///
+/// For an implementation example, see the implementation of this trait
+/// for [`Vec`].
+pub trait Buffer<T: Default> {
+    /// Allocates a buffer of `len` elements, filled with the default.
+    fn allocate(len: usize) -> Self;
+
+    fn as_ptr(&self) -> *const T;
+
+    /// Returns a slice view of `size` elements of the given memory.
+    ///
+    /// # Safety
+    ///
+    /// The caller must not request more elements than are allocated.
+    unsafe fn as_mut_slice(&mut self, len: usize) -> &mut [T];
+
+    /// Consumes this ownership and returns a pointer to the start of the arena.
+    fn into_ptr(self) -> NonNull<T>;
+
+    /// "Adopts" the memory at the given pointer, taking it under management.
+    ///
+    /// Running the operation:
+    ///
+    /// ```
+    /// # use libpam_sys_helpers::memory::Buffer;
+    /// # fn test<T: Default, OwnerType: Buffer<T>>(bytes: usize) {
+    /// let owner = OwnerType::allocate(bytes);
+    /// let ptr = owner.into_ptr();
+    /// let owner = unsafe { OwnerType::from_ptr(ptr, bytes) };
+    /// # }
+    /// ```
+    ///
+    /// must be a no-op.
+    ///
+    /// # Safety
+    ///
+    /// The pointer must be valid, and the caller must provide the exact size
+    /// of the given arena.
+    unsafe fn from_ptr(ptr: NonNull<T>, bytes: usize) -> Self;
+}
+
+impl<T: Default> Buffer<T> for Vec<T> {
+    fn allocate(bytes: usize) -> Self {
+        (0..bytes).map(|_| Default::default()).collect()
+    }
+
+    fn as_ptr(&self) -> *const T {
+        Vec::as_ptr(self)
+    }
+
+    unsafe fn as_mut_slice(&mut self, bytes: usize) -> &mut [T] {
+        debug_assert!(bytes <= self.len());
+        Vec::as_mut(self)
+    }
+
+    fn into_ptr(self) -> NonNull<T> {
+        let mut me = ManuallyDrop::new(self);
+        // SAFETY: a Vec is guaranteed to have a nonzero pointer.
+        unsafe { NonNull::new_unchecked(me.as_mut_ptr()) }
+    }
+
+    unsafe fn from_ptr(ptr: NonNull<T>, bytes: usize) -> Self {
+        Vec::from_raw_parts(ptr.as_ptr(), bytes, bytes)
+    }
+}
+
+/// The structure of the "binary message" payload for the `PAM_BINARY_PROMPT`
+/// extension from Linux-PAM.
+pub struct BinaryPayload {
+    /// The total byte size of the message, including this header,
+    /// as a u32 in network byte order (big endian).
+    pub total_bytes_u32be: [u8; 4],
+    /// A tag used to provide some kind of hint as to what the data is.
+    /// Its meaning is undefined.
+    pub data_type: u8,
+    /// Where the data itself would start, used as a marker to make this
+    /// not [`Unpin`] (since it is effectively an intrusive data structure
+    /// pointing to immediately after itself).
+    pub _marker: PhantomData<PhantomPinned>,
+}
+
+impl BinaryPayload {
+    /// The most data it's possible to put into a [`BinaryPayload`].
+    pub const MAX_SIZE: usize = (u32::MAX - 5) as usize;
+
+    /// Fills in the provided buffer with the given data.
+    ///
+    /// This uses [`copy_from_slice`](slice::copy_from_slice) internally,
+    /// so `buf` must be exactly 5 bytes longer than `data`, or this function
+    /// will panic.
+    pub fn fill(buf: &mut [u8], data_type: u8, data: &[u8]) {
+        let ptr: *mut Self = buf.as_mut_ptr().cast();
+        // SAFETY: We're given a slice, which always has a nonzero pointer.
+        let me = unsafe { ptr.as_mut().unwrap_unchecked() };
+        me.total_bytes_u32be = u32::to_be_bytes(buf.len() as u32);
+        me.data_type = data_type;
+        buf[5..].copy_from_slice(data)
+    }
+
+    /// The total storage needed for the message, including header.
+    pub fn total_bytes(&self) -> usize {
+        u32::from_be_bytes(self.total_bytes_u32be) as usize
+    }
+
+    /// Gets the total byte buffer of the BinaryMessage stored at the pointer.
+    ///
+    /// The returned data slice is borrowed from where the pointer points to.
+    ///
+    /// # Safety
+    ///
+    /// - The pointer must point to a valid `BinaryPayload`.
+    /// - The borrowed data must not outlive the pointer's validity.
+    pub unsafe fn buffer_of<'a>(ptr: *const Self) -> &'a [u8] {
+        let header: &Self = ptr.as_ref().unwrap_unchecked();
+        slice::from_raw_parts(ptr.cast(), header.total_bytes().max(5))
+    }
+
+    /// Gets the contents of the BinaryMessage stored at the given pointer.
+    ///
+    /// The returned data slice is borrowed from where the pointer points to.
+    /// This is a cheap operation and doesn't do *any* copying.
+    ///
+    /// We don't take a `&self` reference here because accessing beyond
+    /// the range of the `Self` data (i.e., beyond the 5 bytes of `self`)
+    /// is undefined behavior. Instead, you have to pass a raw pointer
+    /// directly to the data.
+    ///
+    /// # Safety
+    ///
+    /// - The pointer must point to a valid `BinaryPayload`.
+    /// - The borrowed data must not outlive the pointer's validity.
+    pub unsafe fn contents<'a>(ptr: *const Self) -> (u8, &'a [u8]) {
+        let header: &Self = ptr.as_ref().unwrap_unchecked();
+        (header.data_type, &Self::buffer_of(ptr)[5..])
+    }
+}
+
+/// A binary message owned by some storage.
+///
+/// This is an owned, memory-managed version of [`BinaryPayload`].
+/// The `O` type manages the memory where the payload lives.
+/// [`Vec<u8>`] is one such manager and can be used when ownership
+/// of the data does not need to transit through PAM.
+#[derive(Debug)]
+pub struct OwnedBinaryPayload<Owner: Buffer<u8>>(Owner);
+
+impl<O: Buffer<u8>> OwnedBinaryPayload<O> {
+    /// Allocates a new OwnedBinaryPayload.
+    ///
+    /// This will return a [`TooBigError`] if you try to allocate too much
+    /// (more than [`BinaryPayload::MAX_SIZE`]).
+    pub fn new(data_type: u8, data: &[u8]) -> Result<Self, TooBigError> {
+        let total_len: u32 = (data.len() + 5).try_into().map_err(|_| TooBigError {
+            size: data.len(),
+            max: BinaryPayload::MAX_SIZE,
+        })?;
+        let total_len = total_len as usize;
+        let mut buf = O::allocate(total_len);
+        // SAFETY: We just allocated this exact size.
+        BinaryPayload::fill(unsafe { buf.as_mut_slice(total_len) }, data_type, data);
+        Ok(Self(buf))
+    }
+
+    /// The contents of the buffer.
+    pub fn contents(&self) -> (u8, &[u8]) {
+        unsafe { BinaryPayload::contents(self.as_ptr()) }
+    }
+
+    /// The total bytes needed to store this, including the header.
+    pub fn total_bytes(&self) -> usize {
+        unsafe { BinaryPayload::buffer_of(self.0.as_ptr().cast()).len() }
+    }
+
+    /// Unwraps this into the raw storage backing it.
+    pub fn into_inner(self) -> O {
+        self.0
+    }
+
+    /// Gets a const pointer to the start of the message's buffer.
+    pub fn as_ptr(&self) -> *const BinaryPayload {
+        self.0.as_ptr().cast()
+    }
+
+    /// Consumes ownership of this message and converts it to a raw pointer
+    /// to the start of the message.
+    ///
+    /// To clean this up, you should eventually pass it into [`Self::from_ptr`]
+    /// with the same `O` ownership type.
+    pub fn into_ptr(self) -> NonNull<BinaryPayload> {
+        self.0.into_ptr().cast()
+    }
+
+    /// Takes ownership of the given pointer.
+    ///
+    /// # Safety
+    ///
+    /// You must provide a valid pointer, allocated by (or equivalent to one
+    /// allocated by) [`Self::new`]. For instance, passing a pointer allocated
+    /// by `malloc` to `OwnedBinaryPayload::<Vec<u8>>::from_ptr` is not allowed.
+    pub unsafe fn from_ptr(ptr: NonNull<BinaryPayload>) -> Self {
+        Self(O::from_ptr(ptr.cast(), ptr.as_ref().total_bytes()))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::ptr;
+
+    type VecPayload = OwnedBinaryPayload<Vec<u8>>;
+
+    #[test]
+    fn test_binary_payload() {
+        let simple_message = &[0u8, 0, 0, 16, 0xff, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+        let empty = &[0u8; 5];
+
+        assert_eq!((0xff, &[0u8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10][..]), unsafe {
+            BinaryPayload::contents(simple_message.as_ptr().cast())
+        });
+        assert_eq!((0x00, &[][..]), unsafe {
+            BinaryPayload::contents(empty.as_ptr().cast())
+        });
+    }
+
+    #[test]
+    fn test_owned_binary_payload() {
+        let (typ, data) = (
+            112,
+            &[0, 1, 1, 8, 9, 9, 9, 8, 8, 1, 9, 9, 9, 1, 1, 9, 7, 2, 5, 3][..],
+        );
+        let payload = VecPayload::new(typ, data).unwrap();
+        assert_eq!((typ, data), payload.contents());
+        let ptr = payload.into_ptr();
+        let payload = unsafe { VecPayload::from_ptr(ptr) };
+        assert_eq!((typ, data), payload.contents());
+    }
+
+    #[test]
+    #[ignore]
+    fn test_owned_too_big() {
+        let data = vec![0xFFu8; 0x1_0000_0001];
+        assert_eq!(
+            TooBigError {
+                max: 0xffff_fffa,
+                size: 0x1_0000_0001
+            },
+            VecPayload::new(5, &data).unwrap_err()
+        )
+    }
+
+    #[cfg(debug_assertions)]
+    #[test]
+    #[should_panic]
+    fn test_new_wrong_size() {
+        let bad_vec = vec![0; 19];
+        let msg = PtrPtrVec::new(bad_vec);
+        let _ = msg.as_ptr::<u64>();
+    }
+
+    #[allow(deprecated)]
+    #[cfg(debug_assertions)]
+    #[test]
+    #[should_panic]
+    fn test_iter_xsso_wrong_size() {
+        unsafe {
+            let _ = PtrPtrVec::<u8>::iter_over_xsso::<f64>(ptr::null(), 1);
+        }
+    }
+
+    #[allow(deprecated)]
+    #[cfg(debug_assertions)]
+    #[test]
+    #[should_panic]
+    fn test_iter_linux_wrong_size() {
+        unsafe {
+            let _ = PtrPtrVec::<u128>::iter_over_linux::<()>(ptr::null(), 1);
+        }
+    }
+
+    #[allow(deprecated)]
+    #[test]
+    fn test_right_size() {
+        let good_vec = vec![(1u64, 2u64), (3, 4), (5, 6)];
+        let ptr = good_vec.as_ptr();
+        let msg = PtrPtrVec::new(good_vec);
+        let msg_ref: *const *const (i64, i64) = msg.as_ptr();
+        assert_eq!(unsafe { *msg_ref }, ptr.cast());
+
+        let linux_result: Vec<(i64, i64)> = unsafe { PtrPtrVec::iter_over_linux(msg_ref, 3) }
+            .cloned()
+            .collect();
+        let xsso_result: Vec<(i64, i64)> = unsafe { PtrPtrVec::iter_over_xsso(msg_ref, 3) }
+            .cloned()
+            .collect();
+        assert_eq!(vec![(1, 2), (3, 4), (5, 6)], linux_result);
+        assert_eq!(vec![(1, 2), (3, 4), (5, 6)], xsso_result);
+        drop(msg)
+    }
+
+    #[allow(deprecated)]
+    #[test]
+    fn test_iter_ptr_ptr() {
+        let strs = vec![Box::new("a"), Box::new("b"), Box::new("c"), Box::new("D")];
+        let ptr: *const *const &str = strs.as_ptr().cast();
+        let got: Vec<&str> = unsafe { PtrPtrVec::iter_over_linux(ptr, 4) }
+            .cloned()
+            .collect();
+        assert_eq!(vec!["a", "b", "c", "D"], got);
+
+        let nums = [-1i8, 2, 3];
+        let ptr = nums.as_ptr();
+        let got: Vec<u8> = unsafe { PtrPtrVec::iter_over_xsso(&ptr, 3) }
+            .cloned()
+            .collect();
+        assert_eq!(vec![255, 2, 3], got);
+    }
+}