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

[Colin Ian King <colin.king@canonical.com>]

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