stm32_i2c: ensure that unexpected ISR can't overwrite stale data

if we get an ISR leftover from a previous read transfer it could use
stale values for priv->dcnt and priv->ptr to overwrite stack that is
no longer in scope. This resets dcnt and ptr on each new
stm32_i2c_process() call to ensure that any unexpected data bytes are
discarded

1 files changed, 10 insertions, 1 deletions

diff --git a/nuttx/arch/arm/src/stm32/stm32_i2c.c b/nuttx/arch/arm/src/stm32/stm32_i2c.c
index c02bf4543..996e8af39 100644
--- a/nuttx/arch/arm/src/stm32/stm32_i2c.c
+++ b/nuttx/arch/arm/src/stm32/stm32_i2c.c
@@ -1600,7 +1600,12 @@ static int stm32_i2c_process(FAR struct i2c_dev_s *dev, FAR struct i2c_msg_s *ms
     stm32_i2c_clrstart(priv);
     
     /* Old transfers are done */
-    
+
+    /* reset ptr and dcnt to ensure an unexpected data 
+       interrupt doesn't overwrite stale data */
+    priv->dcnt = 0;
+    priv->ptr = NULL;
+
     priv->msgv = msgs;
     priv->msgc = count;
     
@@ -1751,6 +1756,10 @@ static int stm32_i2c_process(FAR struct i2c_dev_s *dev, FAR struct i2c_msg_s *ms
     
     stm32_i2c_enablefsmc(ahbenr);
     stm32_i2c_sem_post(dev);
+
+    /* ensure that any ISR happening after we finish can't overwrite any user data */
+    priv->dcnt = 0;
+    priv->ptr = NULL;
     
     return -errval;
 }