out of bounds access on array error_text[] because of -ETIMEDOUT return from __send_command()

out of bounds access on array error_text[] because of -ETIMEDOUT return from __send_command()

[Colin Ian King]

Hi,

static analysis with coverity has found a buffer overflow issue with the
brcmstb driver, I believe it may have been introduced with the following
commit:

commit a7c25759d8d84b64c437a78f05df7314b02934e5
Author: Markus Mayer <mmayer@broadcom.com>
Date:   Tue Apr 2 16:01:00 2019 -0700

    memory: brcmstb: dpfe: wait for DCPU to be ready

The static analysis is as follows for the source file
/drivers/memory/brcmstb_dpfe.c :

684 static ssize_t generic_show(unsigned int command, u32 response[],
685                            struct brcmstb_dpfe_priv *priv, char *buf)
686 {
687        int ret;
688
   1. Condition !priv, taking false branch.

689        if (!priv)
690                return sprintf(buf, "ERROR: driver private data not
set\n");
691
   2. return_constant: Function call __send_command(priv, command,
response) may return -110.
   3. assignment: Assigning: ret = __send_command(priv, command,
response). The value of ret is now -110.

692        ret = __send_command(priv, command, response);
   4. Condition ret < 0, taking true branch.

693        if (ret < 0)

Out-of-bounds read (OVERRUN)
   5. overrun-local: Overrunning array error_text of 6 8-byte elements
at element index 110 (byte offset 887) using index -ret (which evaluates
to 110).
694                return sprintf(buf, "ERROR: %s\n", error_text[-ret]);
695
696        return 0;
697 }


Function __send_command() can return -ETIMEDOUT and this causes an
out-of-bounds access on error_text[].

Colin

Re: out of bounds access on array error_text[] because of -ETIMEDOUT return from __send_command()

[Florian Fainelli]

On 8/18/20 5:21 AM, Colin Ian King wrote:
> Hi,
> 
> static analysis with coverity has found a buffer overflow issue with the
> brcmstb driver, I believe it may have been introduced with the following
> commit:
> 
> commit a7c25759d8d84b64c437a78f05df7314b02934e5
> Author: Markus Mayer <mmayer@broadcom.com>
> Date:   Tue Apr 2 16:01:00 2019 -0700
> 
>     memory: brcmstb: dpfe: wait for DCPU to be ready
> 
> The static analysis is as follows for the source file
> /drivers/memory/brcmstb_dpfe.c :
> 
> 684 static ssize_t generic_show(unsigned int command, u32 response[],
> 685                            struct brcmstb_dpfe_priv *priv, char *buf)
> 686 {
> 687        int ret;
> 688
>    1. Condition !priv, taking false branch.
> 
> 689        if (!priv)
> 690                return sprintf(buf, "ERROR: driver private data not
> set\n");
> 691
>    2. return_constant: Function call __send_command(priv, command,
> response) may return -110.
>    3. assignment: Assigning: ret = __send_command(priv, command,
> response). The value of ret is now -110.
> 
> 692        ret = __send_command(priv, command, response);
>    4. Condition ret < 0, taking true branch.
> 
> 693        if (ret < 0)
> 
> Out-of-bounds read (OVERRUN)
>    5. overrun-local: Overrunning array error_text of 6 8-byte elements
> at element index 110 (byte offset 887) using index -ret (which evaluates
> to 110).
> 694                return sprintf(buf, "ERROR: %s\n", error_text[-ret]);
> 695
> 696        return 0;
> 697 }
> 
> 
> Function __send_command() can return -ETIMEDOUT and this causes an
> out-of-bounds access on error_text[].

Markus, what do you think of this:

diff --git a/drivers/memory/brcmstb_dpfe.c b/drivers/memory/brcmstb_dpfe.c
index 60e8633b1175..b41c6251ddc3 100644
--- a/drivers/memory/brcmstb_dpfe.c
+++ b/drivers/memory/brcmstb_dpfe.c
@@ -445,7 +445,7 @@ static int __send_command(struct brcmstb_dpfe_priv
*priv, unsigned int cmd,
        }
        if (resp != 0) {
                mutex_unlock(&priv->lock);
-               return -ETIMEDOUT;
+               return -ffs(DCPU_RET_ERR_TIMEDOUT);
        }

        /* Compute checksum over the message */

That way we only return DCPU-style error code from __send_command and we
de-reference error_text accordingly? Or we could just introduce a proper
lookup with a function instead of a direct array de-reference.
-- 
Florian

Re: out of bounds access on array error_text[] because of -ETIMEDOUT return from __send_command()

[Markus Mayer]

On Wed, 19 Aug 2020 at 11:34, Florian Fainelli <f.fainelli@gmail.com> wrote:
>
> On 8/18/20 5:21 AM, Colin Ian King wrote:
> > Hi,
> >
> > static analysis with coverity has found a buffer overflow issue with the
> > brcmstb driver, I believe it may have been introduced with the following
> > commit:
> >
> > commit a7c25759d8d84b64c437a78f05df7314b02934e5
> > Author: Markus Mayer <mmayer@broadcom.com>
> > Date:   Tue Apr 2 16:01:00 2019 -0700
> >
> >     memory: brcmstb: dpfe: wait for DCPU to be ready
> >
> > The static analysis is as follows for the source file
> > /drivers/memory/brcmstb_dpfe.c :
> >
> > 684 static ssize_t generic_show(unsigned int command, u32 response[],
> > 685                            struct brcmstb_dpfe_priv *priv, char *buf)
> > 686 {
> > 687        int ret;
> > 688
> >    1. Condition !priv, taking false branch.
> >
> > 689        if (!priv)
> > 690                return sprintf(buf, "ERROR: driver private data not
> > set\n");
> > 691
> >    2. return_constant: Function call __send_command(priv, command,
> > response) may return -110.
> >    3. assignment: Assigning: ret = __send_command(priv, command,
> > response). The value of ret is now -110.
> >
> > 692        ret = __send_command(priv, command, response);
> >    4. Condition ret < 0, taking true branch.
> >
> > 693        if (ret < 0)
> >
> > Out-of-bounds read (OVERRUN)
> >    5. overrun-local: Overrunning array error_text of 6 8-byte elements
> > at element index 110 (byte offset 887) using index -ret (which evaluates
> > to 110).
> > 694                return sprintf(buf, "ERROR: %s\n", error_text[-ret]);
> > 695
> > 696        return 0;
> > 697 }
> >
> >
> > Function __send_command() can return -ETIMEDOUT and this causes an
> > out-of-bounds access on error_text[].
>
> Markus, what do you think of this:
>
> diff --git a/drivers/memory/brcmstb_dpfe.c b/drivers/memory/brcmstb_dpfe.c
> index 60e8633b1175..b41c6251ddc3 100644
> --- a/drivers/memory/brcmstb_dpfe.c
> +++ b/drivers/memory/brcmstb_dpfe.c
> @@ -445,7 +445,7 @@ static int __send_command(struct brcmstb_dpfe_priv
> *priv, unsigned int cmd,
>         }
>         if (resp != 0) {
>                 mutex_unlock(&priv->lock);
> -               return -ETIMEDOUT;
> +               return -ffs(DCPU_RET_ERR_TIMEDOUT);
>         }
>
>         /* Compute checksum over the message */
>
> That way we only return DCPU-style error code from __send_command and we
> de-reference error_text accordingly? Or we could just introduce a proper
> lookup with a function instead of a direct array de-reference.

Let me do some experiments. What you are proposing should work and is
in line with the current code. A lookup function might be cleaner,
though.

Thanks,
-Markus

> --
> Florian

Re: out of bounds access on array error_text[] because of -ETIMEDOUT return from __send_command()

[Markus Mayer]

On Thu, 20 Aug 2020 at 10:23, Markus Mayer <mmayer@broadcom.com> wrote:
>
> On Wed, 19 Aug 2020 at 11:34, Florian Fainelli <f.fainelli@gmail.com> wrote:
> >
> > On 8/18/20 5:21 AM, Colin Ian King wrote:
> > > Hi,
> > >
> > > static analysis with coverity has found a buffer overflow issue with the
> > > brcmstb driver, I believe it may have been introduced with the following
> > > commit:
> > >
> > > commit a7c25759d8d84b64c437a78f05df7314b02934e5
> > > Author: Markus Mayer <mmayer@broadcom.com>
> > > Date:   Tue Apr 2 16:01:00 2019 -0700
> > >
> > >     memory: brcmstb: dpfe: wait for DCPU to be ready
> > >
> > > The static analysis is as follows for the source file
> > > /drivers/memory/brcmstb_dpfe.c :
> > >
> > > 684 static ssize_t generic_show(unsigned int command, u32 response[],
> > > 685                            struct brcmstb_dpfe_priv *priv, char *buf)
> > > 686 {
> > > 687        int ret;
> > > 688
> > >    1. Condition !priv, taking false branch.
> > >
> > > 689        if (!priv)
> > > 690                return sprintf(buf, "ERROR: driver private data not
> > > set\n");
> > > 691
> > >    2. return_constant: Function call __send_command(priv, command,
> > > response) may return -110.
> > >    3. assignment: Assigning: ret = __send_command(priv, command,
> > > response). The value of ret is now -110.
> > >
> > > 692        ret = __send_command(priv, command, response);
> > >    4. Condition ret < 0, taking true branch.
> > >
> > > 693        if (ret < 0)
> > >
> > > Out-of-bounds read (OVERRUN)
> > >    5. overrun-local: Overrunning array error_text of 6 8-byte elements
> > > at element index 110 (byte offset 887) using index -ret (which evaluates
> > > to 110).
> > > 694                return sprintf(buf, "ERROR: %s\n", error_text[-ret]);
> > > 695
> > > 696        return 0;
> > > 697 }
> > >
> > >
> > > Function __send_command() can return -ETIMEDOUT and this causes an
> > > out-of-bounds access on error_text[].
> >
> > Markus, what do you think of this:
> >
> > diff --git a/drivers/memory/brcmstb_dpfe.c b/drivers/memory/brcmstb_dpfe.c
> > index 60e8633b1175..b41c6251ddc3 100644
> > --- a/drivers/memory/brcmstb_dpfe.c
> > +++ b/drivers/memory/brcmstb_dpfe.c
> > @@ -445,7 +445,7 @@ static int __send_command(struct brcmstb_dpfe_priv
> > *priv, unsigned int cmd,
> >         }
> >         if (resp != 0) {
> >                 mutex_unlock(&priv->lock);
> > -               return -ETIMEDOUT;
> > +               return -ffs(DCPU_RET_ERR_TIMEDOUT);
> >         }
> >
> >         /* Compute checksum over the message */
> >
> > That way we only return DCPU-style error code from __send_command and we
> > de-reference error_text accordingly? Or we could just introduce a proper
> > lookup with a function instead of a direct array de-reference.
>
> Let me do some experiments. What you are proposing should work and is
> in line with the current code. A lookup function might be cleaner,
> though.

I submitted a patch for review. See https://lkml.org/lkml/2020/8/20/2291.

Regards,
-Markus