nvmem: core: fix possibly memleak when use nvmem_cell_info_to_nvmem_cell()

Fix missing 'kfree_const(cell->name)' when call to
nvmem_cell_info_to_nvmem_cell() in several places:

     * after nvmem_cell_info_to_nvmem_cell() failed during
       nvmem_add_cells()

     * during nvmem_device_cell_{read,write} when cell->name is
       kstrdup'ed() without calling kfree_const() at the end, but
       really there is no reason to do that 'dup, because the cell
       instance is allocated on the stack for some short period to be
       read/write without exposing it to the caller.

So the new nvmem_cell_info_to_nvmem_cell_nodup() helper is introduced
which is used to convert cell_info -> cell without name duplication as
a lighweight version of nvmem_cell_info_to_nvmem_cell().

Fixes: e2a5402e ("nvmem: Add nvmem_device based consumer apis.")
Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Acked-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Vadym Kochan <vadym.kochan@plvision.eu>
Link: https://lore.kernel.org/r/20200923204456.14032-1-vadym.kochan@plvision.euSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/core.c

@@ -361,16 +361,14 @@ static void nvmem_cell_add(struct nvmem_cell *cell)
 	blocking_notifier_call_chain(&nvmem_notifier, NVMEM_CELL_ADD, cell);
 }
 
-static int nvmem_cell_info_to_nvmem_cell(struct nvmem_device *nvmem,
+static int nvmem_cell_info_to_nvmem_cell_nodup(struct nvmem_device *nvmem,
 					const struct nvmem_cell_info *info,
 					struct nvmem_cell *cell)
 {
 	cell->nvmem = nvmem;
 	cell->offset = info->offset;
 	cell->bytes = info->bytes;
-	cell->name = kstrdup_const(info->name, GFP_KERNEL);
-	if (!cell->name)
-		return -ENOMEM;
+	cell->name = info->name;
 
 	cell->bit_offset = info->bit_offset;
 	cell->nbits = info->nbits;
@@ -382,13 +380,30 @@ static int nvmem_cell_info_to_nvmem_cell(struct nvmem_device *nvmem,
 	if (!IS_ALIGNED(cell->offset, nvmem->stride)) {
 		dev_err(&nvmem->dev,
 			"cell %s unaligned to nvmem stride %d\n",
-			cell->name, nvmem->stride);
+			cell->name ?: "<unknown>", nvmem->stride);
 		return -EINVAL;
 	}
 
 	return 0;
 }
 
+static int nvmem_cell_info_to_nvmem_cell(struct nvmem_device *nvmem,
+				const struct nvmem_cell_info *info,
+				struct nvmem_cell *cell)
+{
+	int err;
+
+	err = nvmem_cell_info_to_nvmem_cell_nodup(nvmem, info, cell);
+	if (err)
+		return err;
+
+	cell->name = kstrdup_const(info->name, GFP_KERNEL);
+	if (!cell->name)
+		return -ENOMEM;
+
+	return 0;
+}
+
 /**
  * nvmem_add_cells() - Add cell information to an nvmem device
  *
@@ -1463,7 +1478,7 @@ ssize_t nvmem_device_cell_read(struct nvmem_device *nvmem,
 	if (!nvmem)
 		return -EINVAL;
 
-	rc = nvmem_cell_info_to_nvmem_cell(nvmem, info, &cell);
+	rc = nvmem_cell_info_to_nvmem_cell_nodup(nvmem, info, &cell);
 	if (rc)
 		return rc;
 
@@ -1493,7 +1508,7 @@ int nvmem_device_cell_write(struct nvmem_device *nvmem,
 	if (!nvmem)
 		return -EINVAL;
 
-	rc = nvmem_cell_info_to_nvmem_cell(nvmem, info, &cell);
+	rc = nvmem_cell_info_to_nvmem_cell_nodup(nvmem, info, &cell);
 	if (rc)
 		return rc;