nvmem: Enforce nvmem stride in the sysfs interface

The 'struct nvmem_config' has a stride attribute that specifies the
needed alignment for accesses into the nvmem.  This is used in
nvmem_cell_info_to_nvmem_cell() but not in the sysfs read/write
functions.  If the alignment is important in one place it's important
everywhere, so let's add enforcement.

For now we'll consider it totally invalid to access with the wrong
alignment.  We could relax this in the read case where we could just
read some extra bytes and throw them away.  Relaxing it in the write
case seems harder (and less safe?) since we'd have to read some data
first and then write it back.  To keep it symmetric we'll just
disallow it in both cases.
Reported-by: NRavi Kumar Bokka <rbokka@codeaurora.org>
Signed-off-by: NDouglas Anderson <dianders@chromium.org>
Reviewed-by: NRavi Kumar Bokka <rbokka@codeaurora.org>
Tested-by: NRavi Kumar Bokka <rbokka@codeaurora.org>
Signed-off-by: NSrinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20200722100705.7772-4-srinivas.kandagatla@linaro.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/core.c

@@ -135,6 +135,9 @@ static ssize_t bin_attr_nvmem_read(struct file *filp, struct kobject *kobj,
 	if (pos >= nvmem->size)
 		return 0;
 
+	if (!IS_ALIGNED(pos, nvmem->stride))
+		return -EINVAL;
+
 	if (count < nvmem->word_size)
 		return -EINVAL;
 
@@ -172,6 +175,9 @@ static ssize_t bin_attr_nvmem_write(struct file *filp, struct kobject *kobj,
 	if (pos >= nvmem->size)
 		return -EFBIG;
 
+	if (!IS_ALIGNED(pos, nvmem->stride))
+		return -EINVAL;
+
 	if (count < nvmem->word_size)
 		return -EINVAL;