Re: [PATCH] i2c: Fix OOB access in trace_event_raw_event_smbus_write

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 21 Aug 2025 01:23:12 +0000
Xiaomeng Zhang <zhangxiaomeng13@huawei.com> wrote:

> The smbus_write tracepoint copies __entry->len bytes into a fixed
> I2C_SMBUS_BLOCK_MAX + 2 buffer. Oversized lengths (e.g., 46)
> exceed the destination and over-read the source buffer, triggering
> OOB warning:
> 
> memcpy: detected field-spanning write (size 48) of single field
> "entry->buf" at include/trace/events/smbus.h:60 (size 34)
> 
> Clamp the copy size to I2C_SMBUS_BLOCK_MAX + 2 before memcpy().
> This only affects tracing and does not change I2C transfer behavior.
> 
> Fixes: 8a325997d95d ("i2c: Add message transfer tracepoints for SMBUS [ver #2]")
> Signed-off-by: Xiaomeng Zhang <zhangxiaomeng13@huawei.com>
> ---
>  include/trace/events/smbus.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/include/trace/events/smbus.h b/include/trace/events/smbus.h
> index 71a87edfc46d..e306d8b928c3 100644
> --- a/include/trace/events/smbus.h
> +++ b/include/trace/events/smbus.h
> @@ -57,6 +57,8 @@ TRACE_EVENT_CONDITION(smbus_write,
>  		case I2C_SMBUS_I2C_BLOCK_DATA:
>  			__entry->len = data->block[0] + 1;
>  		copy:
> +			if (__entry->len > I2C_SMBUS_BLOCK_MAX + 2)
> +				__entry->len = I2C_SMBUS_BLOCK_MAX + 2;
>  			memcpy(__entry->buf, data->block, __entry->len);
>  			break;
>  		case I2C_SMBUS_QUICK:

The code has:

                switch (protocol) {
                case I2C_SMBUS_BYTE_DATA:
                        __entry->len = 1;
                        goto copy;
                case I2C_SMBUS_WORD_DATA:
                case I2C_SMBUS_PROC_CALL:
                        __entry->len = 2;
                        goto copy;
                case I2C_SMBUS_BLOCK_DATA:
                case I2C_SMBUS_BLOCK_PROC_CALL:
                case I2C_SMBUS_I2C_BLOCK_DATA:
                        __entry->len = data->block[0] + 1;
                copy:   
                        memcpy(__entry->buf, data->block, __entry->len);
                        break;
                case I2C_SMBUS_QUICK:
                case I2C_SMBUS_BYTE:
                case I2C_SMBUS_I2C_BLOCK_BROKEN:
                default:
                        __entry->len = 0;
                }

I only see two calls to the copy where one is len = 1 and the other is
len = 2. Why not put the check before the copy label?

-- Steve