[PATCH 6.18 042/175] rust_binder: add additional alignment checks

Greg Kroah-Hartman
2026-02-09T14:27:25Z

From: Alice Ryhl <aliceryhl@google.com>

commit d047248190d86a52164656d47bec9bfba61dc71e upstream.

This adds some alignment checks to match C Binder more closely. This
causes the driver to reject more transactions. I don't think any of the
transactions in question are harmful, but it's still a bug because it's
the wrong uapi to accept them.

The cases where usize is changed for u64, it will affect only 32-bit
kernels.

Cc: stable@vger.kernel.org
Fixes: eafedbc7c050 ("rust_binder: add Rust Binder driver")
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Carlos Llamas <cmllamas@google.com>
Link: https://patch.msgid.link/20260123-binder-alignment-more-checks-v1-1-7e1cea77411d@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/android/binder/thread.rs | 50 +++++++++++++++++++++++---------
1 file changed, 36 insertions(+), 14 deletions(-)

diff --git a/drivers/android/binder/thread.rs b/drivers/android/binder/thread.rs
index dcd47e10aeb8..e0ea33ccfe58 100644
--- a/drivers/android/binder/thread.rs
+++ b/drivers/android/binder/thread.rs
@@ -39,6 +39,10 @@
sync::atomic::{AtomicU32, Ordering},
};

+fn is_aligned(value: usize, to: usize) -> bool {
+ value % to == 0
+}
+
/// Stores the layout of the scatter-gather entries. This is used during the `translate_objects`
/// call and is discarded when it returns.
struct ScatterGatherState {
@@ -795,6 +799,10 @@ fn translate_object(
let num_fds = usize::try_from(obj.num_fds).map_err(|_| EINVAL)?;
let fds_len = num_fds.checked_mul(size_of::<u32>()).ok_or(EINVAL)?;

+ if !is_aligned(parent_offset, size_of::<u32>()) {
+ return Err(EINVAL.into());
+ }
+
let info = sg_state.validate_parent_fixup(parent_index, parent_offset, fds_len)?;
view.alloc.info_add_fd_reserve(num_fds)?;

@@ -809,6 +817,10 @@ fn translate_object(
}
};

+ if !is_aligned(parent_entry.sender_uaddr, size_of::<u32>()) {
+ return Err(EINVAL.into());
+ }
+
parent_entry.fixup_min_offset = info.new_min_offset;
parent_entry
.pointer_fixups
@@ -825,6 +837,7 @@ fn translate_object(
.sender_uaddr
.checked_add(parent_offset)
.ok_or(EINVAL)?;
+
let mut fda_bytes = KVec::new();
UserSlice::new(UserPtr::from_addr(fda_uaddr as _), fds_len)
.read_all(&mut fda_bytes, GFP_KERNEL)?;
@@ -958,25 +971,30 @@ pub(crate) fn copy_transaction_data(

let data_size = trd.data_size.try_into().map_err(|_| EINVAL)?;
let aligned_data_size = ptr_align(data_size).ok_or(EINVAL)?;
- let offsets_size = trd.offsets_size.try_into().map_err(|_| EINVAL)?;
- let aligned_offsets_size = ptr_align(offsets_size).ok_or(EINVAL)?;
- let buffers_size = tr.buffers_size.try_into().map_err(|_| EINVAL)?;
- let aligned_buffers_size = ptr_align(buffers_size).ok_or(EINVAL)?;
+ let offsets_size: usize = trd.offsets_size.try_into().map_err(|_| EINVAL)?;
+ let buffers_size: usize = tr.buffers_size.try_into().map_err(|_| EINVAL)?;
let aligned_secctx_size = match secctx.as_ref() {
Some((_offset, ctx)) => ptr_align(ctx.len()).ok_or(EINVAL)?,
None => 0,
};

+ if !is_aligned(offsets_size, size_of::<u64>()) {
+ return Err(EINVAL.into());
+ }
+ if !is_aligned(buffers_size, size_of::<u64>()) {
+ return Err(EINVAL.into());
+ }
+
// This guarantees that at least `sizeof(usize)` bytes will be allocated.
let len = usize::max(
aligned_data_size
- .checked_add(aligned_offsets_size)
- .and_then(|sum| sum.checked_add(aligned_buffers_size))
+ .checked_add(offsets_size)
+ .and_then(|sum| sum.checked_add(buffers_size))
.and_then(|sum| sum.checked_add(aligned_secctx_size))
.ok_or(ENOMEM)?,
- size_of::<usize>(),
+ size_of::<u64>(),
);
- let secctx_off = aligned_data_size + aligned_offsets_size + aligned_buffers_size;
+ let secctx_off = aligned_data_size + offsets_size + buffers_size;
let mut alloc =
match to_process.buffer_alloc(debug_id, len, is_oneway, self.process.task.pid()) {
Ok(alloc) => alloc,
@@ -1008,13 +1026,13 @@ pub(crate) fn copy_transaction_data(
}

let offsets_start = aligned_data_size;
- let offsets_end = aligned_data_size + aligned_offsets_size;
+ let offsets_end = aligned_data_size + offsets_size;

// This state is used for BINDER_TYPE_PTR objects.
let sg_state = sg_state.insert(ScatterGatherState {
unused_buffer_space: UnusedBufferSpace {
offset: offsets_end,
- limit: len,
+ limit: offsets_end + buffers_size,
},
sg_entries: KVec::new(),
ancestors: KVec::new(),
@@ -1023,12 +1041,16 @@ pub(crate) fn copy_transaction_data(
// Traverse the objects specified.
let mut view = AllocationView::new(&mut alloc, data_size);
for (index, index_offset) in (offsets_start..offsets_end)
- .step_by(size_of::<usize>())
+ .step_by(size_of::<u64>())
.enumerate()
{
- let offset = view.alloc.read(index_offset)?;
+ let offset: usize = view
+ .alloc
+ .read::<u64>(index_offset)?
+ .try_into()
+ .map_err(|_| EINVAL)?;

- if offset < end_of_previous_object {
+ if offset < end_of_previous_object || !is_aligned(offset, size_of::<u32>()) {
pr_warn!("Got transaction with invalid offset.");
return Err(EINVAL.into());
}
@@ -1060,7 +1082,7 @@ pub(crate) fn copy_transaction_data(
}

// Update the indexes containing objects to clean up.
- let offset_after_object = index_offset + size_of::<usize>();
+ let offset_after_object = index_offset + size_of::<u64>();
view.alloc
.set_info_offsets(offsets_start..offset_after_object);
}
--
2.53.0