[PATCH net-next v4] rust: net: netlink: validate attribute length before casting to `c_int`
From: Sagar Taunk <hidden>
Date: 2026-09-23 12:05:34
Also in:
lkml, rust-for-linux
Subsystem:
networking [general], rust, the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Miguel Ojeda, Linus Torvalds
`put()` trusted an unchecked `as` cast from `usize` to `c_int`.
When the length exceeds `i32::MAX` that cast wraps around to a
negative value.
This ultimately resulted in a kernel panic when the reinterpreted
value via `__nla_reserve()` and `skb_put()` became enormous.
Validate payload and header both fit together in a `u16`, rejecting
any payload that wouldn't leave room for `NLA_HDRLEN`.
Fixes: 5eaa5fbb6e6c ("rust: netlink: add raw netlink abstraction")
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Sagar Taunk <redacted>
---
Changes Since V3:
Rebased on the upstream rust-next tree.
No functional changes.
rust/kernel/net/netlink.rs | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/rust/kernel/net/netlink.rs b/rust/kernel/net/netlink.rs
index 22ef3dde36fa..2f8733a694a9 100644
--- a/rust/kernel/net/netlink.rs
+++ b/rust/kernel/net/netlink.rs@@ -11,6 +11,7 @@ use kernel::{ alloc::{self, AllocError}, error::to_result, + num::casts::u16_as_usize, prelude::*, transmute::AsBytes, types::Opaque,
@@ -86,9 +87,17 @@ fn put<T>(&mut self, attrtype: c_int, value: &T) -> Result where T: ?Sized + AsBytes, { + // `nla_len` is a 16-bit field that encodes the total attribute length + // (header + payload). Subtracting the header size from `u16::MAX` gives + // the largest payload that still fits within that field. + const MAX_PAYLOAD_LEN: usize = u16_as_usize(u16::MAX) - size_of::<bindings::nlattr>(); + let skb = self.skb.skb.as_ptr(); let len = size_of_val(value); let ptr = core::ptr::from_ref(value).cast::<c_void>(); + if len > MAX_PAYLOAD_LEN { + return Err(EMSGSIZE); + } // SAFETY: `skb` is valid by `NetlinkSkBuff` type invariants, and the provided value is // readable and initialized for its `size_of` bytes. to_result(unsafe { bindings::nla_put(skb, attrtype, len as c_int, ptr) })
--
2.55.0