[RFC PATCH v2 00/12] Socket type control for Landlock
Mikhail Ivanov
ivanov.mikhail1 at huawei-partners.com
Tue Jun 11 11:35:41 UTC 2024
6/10/2024 11:03 AM, Günther Noack wrote:
> On Thu, Jun 06, 2024 at 02:44:23PM +0300, Mikhail Ivanov wrote:
>> 6/4/2024 11:22 PM, Günther Noack wrote:
>> I figured out that I define LANDLOCK_SHIFT_ACCESS_SOCKET macro in
>> really strange way (see landlock/limits.h):
>>
>> #define LANDLOCK_SHIFT_ACCESS_SOCKET LANDLOCK_NUM_ACCESS_SOCKET
>>
>> With this definition, socket access mask overlaps the fs access
>> mask in ruleset->access_masks[layer_level]. That's why
>> landlock_get_fs_access_mask() returns non-zero mask in hook_file_open().
>>
>> So, the macro must be defined in this way:
>>
>> #define LANDLOCK_SHIFT_ACCESS_SOCKET (LANDLOCK_NUM_ACCESS_NET +
>> LANDLOCK_NUM_ACCESS_FS)
>>
>> With this fix, open() doesn't fail in your example.
>>
>> I'm really sorry that I somehow made such a stupid typo. I will try my
>> best to make sure this doesn't happen again.
>
> I found that we had the exact same bug with a wrongly defined "SHIFT" value in
> [1].
>
> Maybe we should define access_masks_t as a bit-field rather than doing the
> bit-shifts by hand. Then the compiler would keep track of the bit-offsets
> automatically.
>
> Bit-fields have a bad reputation, but in my understanding, this is largely
> because they make it hard to control the exact bit-by-bit layout. In our case,
> we do not need such an exact control though, and it would be fine.
>
> To quote Linus Torvalds on [2],
>
> Bitfields are fine if you don't actually care about the underlying format,
> and want gcc to just randomly assign bits, and want things to be
> convenient in that situation.
>
> Let me send you a proposal patch which replaces access_masks_t with a bit-field
> and removes the need for the "SHIFT" definition, which we already got wrong in
> two patch sets now. It has the additional benefit of making the code a bit
> shorter and also removing a few static_assert()s which are now guaranteed by the
> compiler.
>
> —Günther
>
> [1] https://lore.kernel.org/all/ZmLEoBfHyUR3nKAV@google.com/
> [2] https://yarchive.net/comp/linux/bitfields.html
Thank you, Günther! It really looks more clear.
This patch should be applied to Landlock separately, right?
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