i2c: core-smbus: don't trace smbus_reply data on errors
diff mbox series

Message ID 20190104004203.116155-1-jsperbeck@google.com
State Superseded
Headers show
Series
  • i2c: core-smbus: don't trace smbus_reply data on errors
Related show

Commit Message

John Sperbeck Jan. 4, 2019, 12:42 a.m. UTC
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@google.com>
---
 drivers/i2c/i2c-core-smbus.c |  2 +-
 include/trace/events/smbus.h | 10 +++++-----
 2 files changed, 6 insertions(+), 6 deletions(-)

Comments

Steven Rostedt Jan. 4, 2019, 2:49 a.m. UTC | #1
On Thu,  3 Jan 2019 16:42:03 -0800
John Sperbeck <jsperbeck@google.com> wrote:

> 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@google.com>
> ---
>  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),

Hmm, instead of tracing nothing, as this is already a "conditional
trace event", why not add to that condition:

	TP_CONDITION(res >= 0 && read_write == I2C_SMBUS_READ),

Unless you want to still trace some data on failure.

-- Steve

>  	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;
Wolfram Sang Feb. 5, 2019, 12:13 p.m. UTC | #2
On Thu, Jan 03, 2019 at 09:49:27PM -0500, Steven Rostedt wrote:
> On Thu,  3 Jan 2019 16:42:03 -0800
> John Sperbeck <jsperbeck@google.com> wrote:
> 
> > 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@google.com>
> > ---
> >  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),
> 
> Hmm, instead of tracing nothing, as this is already a "conditional
> trace event", why not add to that condition:
> 
> 	TP_CONDITION(res >= 0 && read_write == I2C_SMBUS_READ),
> 
> Unless you want to still trace some data on failure.

John, any comment to this?
John Sperbeck Feb. 5, 2019, 5:19 p.m. UTC | #3
On Tue, Feb 5, 2019 at 4:14 AM Wolfram Sang <wsa@the-dreams.de> wrote:
>
> On Thu, Jan 03, 2019 at 09:49:27PM -0500, Steven Rostedt wrote:
> > On Thu,  3 Jan 2019 16:42:03 -0800
> > John Sperbeck <jsperbeck@google.com> wrote:
> >
> > > 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@google.com>
> > > ---
> > >  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),
> >
> > Hmm, instead of tracing nothing, as this is already a "conditional
> > trace event", why not add to that condition:
> >
> >       TP_CONDITION(res >= 0 && read_write == I2C_SMBUS_READ),
> >
> > Unless you want to still trace some data on failure.
>
> John, any comment to this?
>

The issue we were dealing with was access to uninitialized memory on the stack.
The change '30f939feaeee i2c: fix kernel memory disclosure in dev interface'
does the initialization, so the tracing code is no longer affected.
We just didn't
have that change in the particular kernel we were testing.

Still, Steven's suggestion seems fine to me.  Would you like me to create a new
patch based on that?
Wolfram Sang Feb. 5, 2019, 7:08 p.m. UTC | #4
> > > Hmm, instead of tracing nothing, as this is already a "conditional
> > > trace event", why not add to that condition:
> > >
> > >       TP_CONDITION(res >= 0 && read_write == I2C_SMBUS_READ),
> > >
> > > Unless you want to still trace some data on failure.
> >
> > John, any comment to this?
> >
> 
> The issue we were dealing with was access to uninitialized memory on the stack.
> The change '30f939feaeee i2c: fix kernel memory disclosure in dev interface'
> does the initialization, so the tracing code is no longer affected.
> We just didn't
> have that change in the particular kernel we were testing.
> 
> Still, Steven's suggestion seems fine to me.  Would you like me to create a new
> patch based on that?

I am not a tracing expert, but all that was said here tell me that it
would be better to have the change. So, yes, please, that would be
appreciated.

Patch
diff mbox series

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;