include/trace/events/smbus.h | 2 ++ 1 file changed, 2 insertions(+)
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:
--
2.34.1On 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
I previously attempted to apply a fix within the i2cdev_ioctl_smbus function. While this approach was successful in preventing the warning, I found that the required changes were quite extensive. The WARN is triggered by the trace_smbus_write tracepoint, which performs a memcpy(__entry->buf, data->block, len) for write operations on three specific block protocols: I2C_SMBUS_BLOCK_DATA, I2C_SMBUS_I2C_BLOCK_DATA, and I2C_SMBUS_BLOCK_PROC_CALL. To fix this in i2cdev_ioctl_smbus, it would be necessary to add checks for all three of these cases, which makes the solution rather complex.
--xiaomeng
-----邮件原件-----
发件人: Steven Rostedt <rostedt@goodmis.org>
发送时间: 2025年9月3日 3:50
收件人: zhangxiaomeng (A) <zhangxiaomeng13@huawei.com>
抄送: mhiramat@kernel.org; dhowells@redhat.com; wsa@kernel.org; linux-kernel@vger.kernel.org; linux-trace-kernel@vger.kernel.org
主题: Re: [PATCH] i2c: Fix OOB access in trace_event_raw_event_smbus_write
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
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