[PATCH] i2c: core-smbus: don't trace smbus_reply data on errors

[John Sperbeck]

If an smbus transfer fails, there's no guarantee that the output
buffer was written.  So, avoid copying from the output buffer when
tracing after an error.  This was 'mostly harmless', but would trip
up kasan checking if left-over cruft in byte 0 is a large length,
causing us to read from unwritten memory.

Signed-off-by: John Sperbeck <jsperbeck@xxxxxxxxxx>
---
 drivers/i2c/i2c-core-smbus.c |  2 +-
 include/trace/events/smbus.h | 10 +++++-----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
index 9cd66cabb84f..132119112596 100644
--- a/drivers/i2c/i2c-core-smbus.c
+++ b/drivers/i2c/i2c-core-smbus.c
@@ -585,7 +585,7 @@ s32 __i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
 trace:
 	/* If enabled, the reply tracepoint is conditional on read_write. */
 	trace_smbus_reply(adapter, addr, flags, read_write,
-			  command, protocol, data);
+			  command, protocol, data, res);
 	trace_smbus_result(adapter, addr, flags, read_write,
 			   command, protocol, res);
 
diff --git a/include/trace/events/smbus.h b/include/trace/events/smbus.h
index d2fb6e1d3e10..b6376a7c7e74 100644
--- a/include/trace/events/smbus.h
+++ b/include/trace/events/smbus.h
@@ -138,8 +138,8 @@ TRACE_EVENT_CONDITION(smbus_reply,
 	TP_PROTO(const struct i2c_adapter *adap,
 		 u16 addr, unsigned short flags,
 		 char read_write, u8 command, int protocol,
-		 const union i2c_smbus_data *data),
-	TP_ARGS(adap, addr, flags, read_write, command, protocol, data),
+		 const union i2c_smbus_data *data, int res),
+	TP_ARGS(adap, addr, flags, read_write, command, protocol, data, res),
 	TP_CONDITION(read_write == I2C_SMBUS_READ),
 	TP_STRUCT__entry(
 		__field(int,	adapter_nr		)
@@ -159,16 +159,16 @@ TRACE_EVENT_CONDITION(smbus_reply,
 		switch (protocol) {
 		case I2C_SMBUS_BYTE:
 		case I2C_SMBUS_BYTE_DATA:
-			__entry->len = 1;
+			__entry->len = res < 0 ? 0 : 1;
 			goto copy;
 		case I2C_SMBUS_WORD_DATA:
 		case I2C_SMBUS_PROC_CALL:
-			__entry->len = 2;
+			__entry->len = res < 0 ? 0 : 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;
+			__entry->len = res < 0 ? 0 : data->block[0] + 1;
 		copy:
 			memcpy(__entry->buf, data->block, __entry->len);
 			break;
-- 
2.20.1.415.g653613c723-goog