linux-kernel - Re: [PATCH] nvmem: core: limit cell sysfs permissions to main attribute ones

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Date: Sat, 22 Jun 2024 12:38:34 +0200 (GMT+02:00)
From: Thomas Weißschuh  <thomas@...ch.de>
To: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc: Thomas Weißschuh <linux@...ssschuh.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Miquel Raynal <miquel.raynal@...tlin.com>,
	Marco Felsch <m.felsch@...gutronix.de>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] nvmem: core: limit cell sysfs permissions to main
 attribute ones

Jun 22, 2024 12:11:04 Srinivas Kandagatla <srinivas.kandagatla@...aro.org>:

>
>
> On 19/06/2024 19:09, Thomas Weißschuh wrote:
>> 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: 0331c611949f ("nvmem: core: Expose cells through sysfs")
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
>> ---
>> This was also discussed as part of
>> "[PATCH] nvmem: core: add sysfs cell write support" [0].
>> But there haven't been updates to that patch and this is arguably a
>> standalone bugfix.
>> [0] https://lore.kernel.org/lkml/20240223154129.1902905-1-m.felsch@pengutronix.de/
>> ---
>>   drivers/nvmem/core.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
>> index e1ec3b7200d7..acfea1e56849 100644
>> --- a/drivers/nvmem/core.c
>> +++ b/drivers/nvmem/core.c
>> @@ -463,7 +463,7 @@ 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);
> Why not just
> attrs[i].attr.mode = nvmem_bin_attr_get_umode(nvmem);

Because nvmem_bin_attr_get_umode() will include write permissions
if the base nvmem device is writable.

But (for now) the cell sysfs attributes do not implement writes.


> ?
>
> --srini
>>         attrs[i].size = entry->bytes;
>>         attrs[i].read = &nvmem_cell_attr_read;
>>         attrs[i].private = entry;
>> ---
>> base-commit: 92e5605a199efbaee59fb19e15d6cc2103a04ec2
>> change-id: 20240619-nvmem-cell-sysfs-perm-156fde0d7460
>> Best regards,