[PATCH 0/3] cast sizeof to int for comparison

[PATCH 0/3] cast sizeof to int for comparison

[Julia Lawall]

Comparing an int to a size, which is unsigned, causes the int to become
unsigned, giving the wrong result.

The semantic match that finds this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@safe disable not_int2@
int x;
position p;
binary operator op = {<,<=};
expression e;
@@

(
x < 0 || (x@p op e)
|
x <= 0 || (x@p op e)
|
x > 0 && (x@p op e)
|
x >= 0 && (x@p op e)
)

@@
int x;
type t;
expression e,e1;
identifier f != {strlen,resource_size};
position p != safe.p;
binary operator op = {<,<=};
@@

*x = f(...);
... when != x = e1
    when != if (x < 0 || ...) { ... return ...; }
(
*x@p op sizeof(e)
|
*x@p op sizeof(t)
)
// </smpl>

---

 drivers/input/mouse/elan_i2c_smbus.c |    2 +-
 drivers/media/usb/gspca/kinect.c     |    2 +-
 drivers/usb/wusbcore/security.c      |    2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

[PATCH 1/3] Input: elan_i2c_smbus - cast sizeof to int for comparison

[Julia Lawall]

Comparing an int to a size, which is unsigned, causes the int to become
unsigned, giving the wrong result.  i2c_smbus_read_block_data can return the
result of i2c_smbus_xfer, whih can return a negative error code.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
int x;
expression e,e1;
identifier f;
@@

*x = f(...);
... when != x = e1
    when != if (x < 0 || ...) { ... return ...; }
*x < sizeof(e)
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>

---
 drivers/input/mouse/elan_i2c_smbus.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/input/mouse/elan_i2c_smbus.c b/drivers/input/mouse/elan_i2c_smbus.c
index c060d27..88e315d 100644
--- a/drivers/input/mouse/elan_i2c_smbus.c
+++ b/drivers/input/mouse/elan_i2c_smbus.c
@@ -387,7 +387,7 @@ static int elan_smbus_prepare_fw_update(struct i2c_client *client)
 		len = i2c_smbus_read_block_data(client,
 						ETP_SMBUS_IAP_PASSWORD_READ,
 						val);
-		if (len < sizeof(u16)) {
+		if (len < (int)sizeof(u16)) {
 			error = len < 0 ? len : -EIO;
 			dev_err(dev, "failed to read iap password: %d\n",
 				error);

Re: [PATCH 1/3] Input: elan_i2c_smbus - cast sizeof to int for comparison

[Dmitry Torokhov]

On Sun, Jul 01, 2018 at 07:32:03PM +0200, Julia Lawall wrote:
> Comparing an int to a size, which is unsigned, causes the int to become
> unsigned, giving the wrong result.  i2c_smbus_read_block_data can return the
> result of i2c_smbus_xfer, whih can return a negative error code.
> 
> A simplified version of the semantic match that finds this problem is as
> follows: (http://coccinelle.lip6.fr/)
> 
> // <smpl>
> @@
> int x;
> expression e,e1;
> identifier f;
> @@
> 
> *x = f(...);
> ... when != x = e1
>     when != if (x < 0 || ...) { ... return ...; }
> *x < sizeof(e)
> // </smpl>
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
> 

Applied, thank you.

> ---
>  drivers/input/mouse/elan_i2c_smbus.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/input/mouse/elan_i2c_smbus.c b/drivers/input/mouse/elan_i2c_smbus.c
> index c060d27..88e315d 100644
> --- a/drivers/input/mouse/elan_i2c_smbus.c
> +++ b/drivers/input/mouse/elan_i2c_smbus.c
> @@ -387,7 +387,7 @@ static int elan_smbus_prepare_fw_update(struct i2c_client *client)
>  		len = i2c_smbus_read_block_data(client,
>  						ETP_SMBUS_IAP_PASSWORD_READ,
>  						val);
> -		if (len < sizeof(u16)) {
> +		if (len < (int)sizeof(u16)) {
>  			error = len < 0 ? len : -EIO;
>  			dev_err(dev, "failed to read iap password: %d\n",
>  				error);
> 

-- 
Dmitry

Re: [PATCH 0/3] cast sizeof to int for comparison

[Joe Perches]

On Sun, 2018-07-01 at 19:32 +0200, Julia Lawall wrote:
> Comparing an int to a size, which is unsigned, causes the int to become
> unsigned, giving the wrong result.
> 
> The semantic match that finds this problem is as follows:
> (http://coccinelle.lip6.fr/)

Great, thanks.

But what about the ones in net/smc like:

> net/smc/smc_clc.c:	
> 
>         len = kernel_sendmsg(smc->clcsock, &msg, &vec, 1,
>                              sizeof(struct smc_clc_msg_decline));
>         if (len < sizeof(struct smc_clc_msg_decline))

Are those detected by the semantic match and ignored?

Re: [PATCH 0/3] cast sizeof to int for comparison

[Julia Lawall]

On Sun, 1 Jul 2018, Joe Perches wrote:

> On Sun, 2018-07-01 at 19:32 +0200, Julia Lawall wrote:
> > Comparing an int to a size, which is unsigned, causes the int to become
> > unsigned, giving the wrong result.
> >
> > The semantic match that finds this problem is as follows:
> > (http://coccinelle.lip6.fr/)
>
> Great, thanks.
>
> But what about the ones in net/smc like:
>
> > net/smc/smc_clc.c:
> >
> >         len = kernel_sendmsg(smc->clcsock, &msg, &vec, 1,
> >                              sizeof(struct smc_clc_msg_decline));
> >         if (len < sizeof(struct smc_clc_msg_decline))
>
> Are those detected by the semantic match and ignored?

I wasn't sure how to justify that kernel_sendmsg returns a negative value.
If it is the case, I can send the patch.  I only found this in one file,
but there were multiple occurrences.

julia

Re: [PATCH 0/3] cast sizeof to int for comparison

[Dan Carpenter]

On Sun, Jul 01, 2018 at 08:51:55PM +0200, Julia Lawall wrote:
> 
> 
> On Sun, 1 Jul 2018, Joe Perches wrote:
> 
> > On Sun, 2018-07-01 at 19:32 +0200, Julia Lawall wrote:
> > > Comparing an int to a size, which is unsigned, causes the int to become
> > > unsigned, giving the wrong result.
> > >
> > > The semantic match that finds this problem is as follows:
> > > (http://coccinelle.lip6.fr/)
> >
> > Great, thanks.
> >
> > But what about the ones in net/smc like:
> >
> > > net/smc/smc_clc.c:
> > >
> > >         len = kernel_sendmsg(smc->clcsock, &msg, &vec, 1,
> > >                              sizeof(struct smc_clc_msg_decline));
> > >         if (len < sizeof(struct smc_clc_msg_decline))
> >
> > Are those detected by the semantic match and ignored?
> 
> I wasn't sure how to justify that kernel_sendmsg returns a negative value.
> If it is the case, I can send the patch.  I only found this in one file,
> but there were multiple occurrences.
> 

In theory, Smatch is supposed to know return values but kernel_sendmsg()
is too complicated for Smatch.  It's a tricky thing...  That particular
check is correct and deliberate, but there is another check which is
wrong.

net/smc/smc_clc.c
   369          len = kernel_sendmsg(smc->clcsock, &msg, &vec, 1,
   370                               sizeof(struct smc_clc_msg_decline));
   371          if (len < sizeof(struct smc_clc_msg_decline))
   372                  smc->sk.sk_err = EPROTO;
   373          if (len < 0)
   374                  smc->sk.sk_err = -len;

If it's invalid we set an error code, if it's already an error we
preserve the error code.

   375          return sock_error(&smc->sk);

[ snip ]

   442          /* due to the few bytes needed for clc-handshake this cannot block */
   443          len = kernel_sendmsg(smc->clcsock, &msg, vec, i, plen);
   444          if (len < sizeof(pclc)) {
   445                  if (len >= 0) {
                            ^^^^^^^^
This is always true.

   446                          reason_code = -ENETUNREACH;
   447                          smc->sk.sk_err = -reason_code;
   448                  } else {
   449                          smc->sk.sk_err = smc->clcsock->sk->sk_err;
   450                          reason_code = -smc->sk.sk_err;
   451                  }
   452          }

The other two checks are not type promoted so they also work as
intended.

This is an interesting sort of bug I've written a Smatch script inspired
by your work here.  One for the type promotion and one for the
impossible condition.  I'll let you know how it goes.

regards,
dan carpenter