nvmem: core: limit cell sysfs permissions to main attribute ones

BugLink: https://bugs.launchpad.net/bugs/2078289

commit 6bef98bafd82903a8d461463f9594f19f1fd6a85 upstream.

The cell sysfs attribute should not provide more access to the nvmem
data than the main attribute itself.
For example if nvme_config::root_only was set, the cell attribute
would still provide read access to everybody.

Mask out permissions not available on the main attribute.

Fixes: 0331c61194 ("nvmem: core: Expose cells through sysfs")
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20240628113704.13742-5-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Portia Stephens <portia.stephens@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/nvmem/core.c

@@ -462,7 +462,7 @@ static int nvmem_populate_sysfs_cells(struct nvmem_device *nvmem)
 						    "%s@%x,%x", entry->name,
 						    entry->offset,
 						    entry->bit_offset);
-		attrs[i].attr.mode = 0444;
+		attrs[i].attr.mode = 0444 & nvmem_bin_attr_get_umode(nvmem);
 		attrs[i].size = entry->bytes;
 		attrs[i].read = &nvmem_cell_attr_read;
 		attrs[i].private = entry;