[PATCH] memory: brcmstb_dpfe: fix array index out of bounds

[Markus Mayer]

We would overrun the error_text array if we hit a TIMEOUT condition,
because we were using the error code "ETIMEDOUT" (which is 110) as an
array index.

We fix the problem by correcting the array index and by providing a
function to retrieve error messages rather than accessing the array
directly. The function includes a bounds check that prevents the array
from being overrun.

Signed-off-by: Markus Mayer <mma...@broadcom.com>
---

This patch was prepared in response to https://lkml.org/lkml/2020/8/18/505.

 drivers/memory/brcmstb_dpfe.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/drivers/memory/brcmstb_dpfe.c b/drivers/memory/brcmstb_dpfe.c
index 81abc4a98a27..a986a849f58e 100644
--- a/drivers/memory/brcmstb_dpfe.c
+++ b/drivers/memory/brcmstb_dpfe.c
@@ -190,11 +190,6 @@ struct brcmstb_dpfe_priv {
        struct mutex lock;
 };
 
-static const char * const error_text[] = {
-       "Success", "Header code incorrect", "Unknown command or argument",
-       "Incorrect checksum", "Malformed command", "Timed out",
-};
-
 /*
  * Forward declaration of our sysfs attribute functions, so we can declare the
  * attribute data structures early.
@@ -307,6 +302,20 @@ static const struct dpfe_api dpfe_api_v3 = {
        },
 };
 
+static const char * const get_error_text(unsigned int i)
+{
+       static const char * const error_text[] = {
+               "Success", "Header code incorrect",
+               "Unknown command or argument", "Incorrect checksum",
+               "Malformed command", "Timed out", "Unknown error",
+       };
+
+       if (unlikely(i >= ARRAY_SIZE(error_text)))
+               i = ARRAY_SIZE(error_text) - 1;
+
+       return error_text[i];
+}
+
 static bool is_dcpu_enabled(struct brcmstb_dpfe_priv *priv)
 {
        u32 val;
@@ -446,7 +455,7 @@ 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 */
@@ -695,7 +704,7 @@ static ssize_t generic_show(unsigned int command, u32 
response[],
 
        ret = __send_command(priv, command, response);
        if (ret < 0)
-               return sprintf(buf, "ERROR: %s\n", error_text[-ret]);
+               return sprintf(buf, "ERROR: %s\n", get_error_text(-ret));
 
        return 0;
 }
-- 
2.17.1