Re: [PATCH] rust_binder: fix oneway spam detection

[Alice Ryhl <aliceryhl@google.com>]

On Tue, Feb 10, 2026 at 11:28:20PM +0000, Carlos Llamas wrote:
> The spam detection logic in TreeRange was executed before the current
> request was inserted into the tree. So the new request was not being
> factored in the spam calculation. Fix this by moving the logic after
> the new range has been inserted.
> 
> Also, the detection logic for ArrayRange was missing altogether which
> meant large spamming transactions could get away without being detected.
> Fix this by implementing an equivalent low_oneway_space() in ArrayRange.
> 
> Note that I looked into centralizing this logic in RangeAllocator but
> iterating through 'state' and 'size' got a bit too complicated (for me)
> and I abandoned this effort.

I think current approach is fine.

> Cc: stable@vger.kernel.org
> Cc: Alice Ryhl <aliceryhl@google.com>
> Fixes: eafedbc7c050 ("rust_binder: add Rust Binder driver")
> Signed-off-by: Carlos Llamas <cmllamas@google.com>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>

> +    /// Find the amount and size of buffers allocated by the current caller.
> +    ///
> +    /// The idea is that once we cross the threshold, whoever is responsible
> +    /// for the low async space is likely to try to send another async transaction,
> +    /// and at some point we'll catch them in the act.  This is more efficient
> +    /// than keeping a map per pid.
> +    fn low_oneway_space(&self, calling_pid: Pid) -> bool {
> +        let mut total_alloc_size = 0;
> +        let mut num_buffers = 0;
> +
> +        // Warn if this pid has more than 50 transactions, or more than 50% of
> +        // async space (which is 25% of total buffer size). Oneway spam is only
> +        // detected when the threshold is exceeded.
> +        for range in &self.ranges {
> +            if range.state.is_oneway() && range.state.pid() == calling_pid {
> +                total_alloc_size += range.size;
> +                num_buffers += 1;
> +            }
> +        }
> +        num_buffers > 50 || total_alloc_size > self.size / 4

The array can never contain 50 buffers, but we should still keep this
check in case that's changed in the future.

Alice