[PATCH v3] nvmem: check invalid number of bytes in nvmem_{read,write}()

[Biju Das <biju.das@xxxxxxxxxxxxxx>]

Add check in nvmem_{read,write}()to ensure that nvmem core never passes
an invalid number of bytes.

Signed-off-by: Biju Das <biju.das@xxxxxxxxxxxxxx>
---
V1-->V2
	* Moved checks from bin_attr_nvmem_{read/write} into nvmem_reg_{read,write}
	* Removed checks from nvmem_device_device_{read,write}()
V2-->V3
	* Changed the Error from "ENOSPC" to "EFBIG" on nvmem_reg_write.
---
 drivers/nvmem/core.c | 97 ++++++++++++++++++++++++++--------------------------
 1 file changed, 49 insertions(+), 48 deletions(-)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index f7301bb..dfbc8ff 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -76,19 +76,60 @@ static struct lock_class_key eeprom_lock_key;
 static int nvmem_reg_read(struct nvmem_device *nvmem, unsigned int offset,
 			  void *val, size_t bytes)
 {
-	if (nvmem->reg_read)
-		return nvmem->reg_read(nvmem->priv, offset, val, bytes);
+	int rc;
+	size_t new_bytes;
+
+	/* Stop the user from reading */
+	if ((offset >= nvmem->size) || (bytes == 0))
+		return 0;
+
+	if ((nvmem->reg_read == NULL) || (bytes < nvmem->word_size))
+		return -EINVAL;
+
+	if (unlikely(check_add_overflow(bytes, offset, &new_bytes)))
+		return -EOVERFLOW;
 
-	return -EINVAL;
+	if (new_bytes > nvmem->size)
+		bytes = nvmem->size - offset;
+
+	bytes = round_down(bytes, nvmem->word_size);
+	rc = nvmem->reg_read(nvmem->priv, offset, val, bytes);
+
+	if (rc)
+		return rc;
+
+	return bytes;
 }
 
 static int nvmem_reg_write(struct nvmem_device *nvmem, unsigned int offset,
 			   void *val, size_t bytes)
 {
-	if (nvmem->reg_write)
-		return nvmem->reg_write(nvmem->priv, offset, val, bytes);
+	int rc;
+	size_t new_bytes;
+
+	/* Stop the user from writing */
+	if (offset >= nvmem->size)
+		return -EFBIG;
+
+	if (bytes == 0)
+		return 0;
+
+	if ((nvmem->reg_write == NULL) || (bytes < nvmem->word_size))
+		return -EINVAL;
+
+	if (unlikely(check_add_overflow(bytes, offset, &new_bytes)))
+		return -EOVERFLOW;
+
+	if (new_bytes > nvmem->size)
+		bytes = nvmem->size - offset;
+
+	bytes = round_down(bytes, nvmem->word_size);
+	rc = nvmem->reg_write(nvmem->priv, offset, val, bytes);
+
+	if (rc)
+		return rc;
 
-	return -EINVAL;
+	return bytes;
 }
 
 static ssize_t type_show(struct device *dev,
@@ -111,33 +152,13 @@ static ssize_t bin_attr_nvmem_read(struct file *filp, struct kobject *kobj,
 				    char *buf, loff_t pos, size_t count)
 {
 	struct device *dev;
-	struct nvmem_device *nvmem;
-	int rc;
 
 	if (attr->private)
 		dev = attr->private;
 	else
 		dev = container_of(kobj, struct device, kobj);
-	nvmem = to_nvmem_device(dev);
-
-	/* Stop the user from reading */
-	if (pos >= nvmem->size)
-		return 0;
-
-	if (count < nvmem->word_size)
-		return -EINVAL;
-
-	if (pos + count > nvmem->size)
-		count = nvmem->size - pos;
-
-	count = round_down(count, nvmem->word_size);
-
-	rc = nvmem_reg_read(nvmem, pos, buf, count);
-
-	if (rc)
-		return rc;
 
-	return count;
+	return nvmem_reg_read(to_nvmem_device(dev), pos, buf, count);
 }
 
 static ssize_t bin_attr_nvmem_write(struct file *filp, struct kobject *kobj,
@@ -145,33 +166,13 @@ static ssize_t bin_attr_nvmem_write(struct file *filp, struct kobject *kobj,
 				     char *buf, loff_t pos, size_t count)
 {
 	struct device *dev;
-	struct nvmem_device *nvmem;
-	int rc;
 
 	if (attr->private)
 		dev = attr->private;
 	else
 		dev = container_of(kobj, struct device, kobj);
-	nvmem = to_nvmem_device(dev);
-
-	/* Stop the user from writing */
-	if (pos >= nvmem->size)
-		return -EFBIG;
-
-	if (count < nvmem->word_size)
-		return -EINVAL;
-
-	if (pos + count > nvmem->size)
-		count = nvmem->size - pos;
-
-	count = round_down(count, nvmem->word_size);
-
-	rc = nvmem_reg_write(nvmem, pos, buf, count);
-
-	if (rc)
-		return rc;
 
-	return count;
+	return nvmem_reg_write(to_nvmem_device(dev), pos, buf, count);
 }
 
 /* default read/write permissions */
-- 
2.7.4