[PATCH] firmware: arm_scmi: Fix possible scmi_linux_errmap buffer overflow

[PATCH] firmware: arm_scmi: Fix possible scmi_linux_errmap buffer overflow

[Sudeep Holla]

The scmi_linux_errmap buffer access index is supposed to depend on the
array size to prevent element out of bounds access. It uses SCMI_ERR_MAX
to check bounds but that can mismatch with the array size. It also
changes the success into -EIO though scmi_linux_errmap is never used in
case of success, it is expected to work for success case too.

It is slightly confusing code as the negative of the error code
is used as index to the buffer. Fix it by negating it at the start and
make it more readable.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
---
 drivers/firmware/arm_scmi/driver.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

(Based on https://lore.kernel.org/r/20210707134739.1869481-1-sudeep.holla@arm.com)

diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index 66e5e694be7d..2a5c1b3658c4 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -166,8 +166,10 @@ static const int scmi_linux_errmap[] = {
 
 static inline int scmi_to_linux_errno(int errno)
 {
-	if (errno < SCMI_SUCCESS && errno > SCMI_ERR_MAX)
-		return scmi_linux_errmap[-errno];
+	int err_idx = -errno;
+
+	if (err_idx >= SCMI_SUCCESS && err_idx < ARRAY_SIZE(scmi_linux_errmap))
+		return scmi_linux_errmap[err_idx];
 	return -EIO;
 }
 
-- 
2.25.1


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Re: [PATCH] firmware: arm_scmi: Fix possible scmi_linux_errmap buffer overflow

[Cristian Marussi]

On Wed, Jul 07, 2021 at 02:50:28PM +0100, Sudeep Holla wrote:
> The scmi_linux_errmap buffer access index is supposed to depend on the
> array size to prevent element out of bounds access. It uses SCMI_ERR_MAX
> to check bounds but that can mismatch with the array size. It also
> changes the success into -EIO though scmi_linux_errmap is never used in
> case of success, it is expected to work for success case too.
> 
> It is slightly confusing code as the negative of the error code
> is used as index to the buffer. Fix it by negating it at the start and
> make it more readable.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> ---
>  drivers/firmware/arm_scmi/driver.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> (Based on https://lore.kernel.org/r/20210707134739.1869481-1-sudeep.holla@arm.com)
> 
> diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> index 66e5e694be7d..2a5c1b3658c4 100644
> --- a/drivers/firmware/arm_scmi/driver.c
> +++ b/drivers/firmware/arm_scmi/driver.c
> @@ -166,8 +166,10 @@ static const int scmi_linux_errmap[] = {
>  
>  static inline int scmi_to_linux_errno(int errno)
>  {
> -	if (errno < SCMI_SUCCESS && errno > SCMI_ERR_MAX)
> -		return scmi_linux_errmap[-errno];
> +	int err_idx = -errno;
> +
> +	if (err_idx >= SCMI_SUCCESS && err_idx < ARRAY_SIZE(scmi_linux_errmap))
> +		return scmi_linux_errmap[err_idx];
>  	return -EIO;
>  }
>  
Hi,

Looks good to me; now SCMI_ERR_MAX is not referenced anymore by anyone
but I suppose is good practice to still keep it as an end-marker for
scmi_error_codes enum.

Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>

Thanks,
Cristian

> -- 
> 2.25.1
> 

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Re: [PATCH] firmware: arm_scmi: Fix possible scmi_linux_errmap buffer overflow

[Sudeep Holla]

On Wed, Jul 07, 2021 at 03:06:25PM +0100, Cristian Marussi wrote:
> On Wed, Jul 07, 2021 at 02:50:28PM +0100, Sudeep Holla wrote:
> > The scmi_linux_errmap buffer access index is supposed to depend on the
> > array size to prevent element out of bounds access. It uses SCMI_ERR_MAX
> > to check bounds but that can mismatch with the array size. It also
> > changes the success into -EIO though scmi_linux_errmap is never used in
> > case of success, it is expected to work for success case too.
> > 
> > It is slightly confusing code as the negative of the error code
> > is used as index to the buffer. Fix it by negating it at the start and
> > make it more readable.
> > 
> > Reported-by: kernel test robot <lkp@intel.com>
> > Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> > Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> > ---
> >  drivers/firmware/arm_scmi/driver.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > (Based on https://lore.kernel.org/r/20210707134739.1869481-1-sudeep.holla@arm.com)
> > 
> > diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> > index 66e5e694be7d..2a5c1b3658c4 100644
> > --- a/drivers/firmware/arm_scmi/driver.c
> > +++ b/drivers/firmware/arm_scmi/driver.c
> > @@ -166,8 +166,10 @@ static const int scmi_linux_errmap[] = {
> >  
> >  static inline int scmi_to_linux_errno(int errno)
> >  {
> > -	if (errno < SCMI_SUCCESS && errno > SCMI_ERR_MAX)
> > -		return scmi_linux_errmap[-errno];
> > +	int err_idx = -errno;
> > +
> > +	if (err_idx >= SCMI_SUCCESS && err_idx < ARRAY_SIZE(scmi_linux_errmap))
> > +		return scmi_linux_errmap[err_idx];
> >  	return -EIO;
> >  }
> >  
> Hi,
> 
> Looks good to me; now SCMI_ERR_MAX is not referenced anymore by anyone
> but I suppose is good practice to still keep it as an end-marker for
> scmi_error_codes enum.
>

Good point, I will drop it as there are no users. It can be added later
if needed.

> Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
>

Thanks !

-- 
Regards,
Sudeep

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Re: [PATCH] firmware: arm_scmi: Fix possible scmi_linux_errmap buffer overflow

[Sudeep Holla]

On Wed, 7 Jul 2021 14:50:28 +0100, Sudeep Holla wrote:
> The scmi_linux_errmap buffer access index is supposed to depend on the
> array size to prevent element out of bounds access. It uses SCMI_ERR_MAX
> to check bounds but that can mismatch with the array size. It also
> changes the success into -EIO though scmi_linux_errmap is never used in
> case of success, it is expected to work for success case too.
> 
> It is slightly confusing code as the negative of the error code
> is used as index to the buffer. Fix it by negating it at the start and
> make it more readable.

Applied to sudeep.holla/linux (for-next/scmi), thanks!

[1/1] firmware: arm_scmi: Fix possible scmi_linux_errmap buffer overflow
      https://git.kernel.org/sudeep.holla/c/7a691f16cc

--
Regards,
Sudeep


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