Re: [PATCH RFC 1/1] Documentation: describe how to add a system call

[David Drysdale]

On Tue, Jul 28, 2015 at 5:43 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Tue, Jul 28, 2015 at 4:41 AM, David Drysdale <drysdale@xxxxxxxxxx> wrote:
>> Add a document describing the process of adding a new system call,
>> including the need for a flags argument for future compatibility, and
>> covering 32-bit/64-bit concerns (albeit in an x86-centric way).
>>
>> Signed-off-by: David Drysdale <drysdale@xxxxxxxxxx>
>> Reviewed-by: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
>
> This is great!
>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
>
> I have a few minor suggestions below...

Thanks, I've applied all bar one -- a query below.

>> ---
>>  Documentation/adding-syscalls.txt | 454 ++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 454 insertions(+)
>>  create mode 100644 Documentation/adding-syscalls.txt
>>
>> diff --git a/Documentation/adding-syscalls.txt b/Documentation/adding-syscalls.txt
>> new file mode 100644
>> index 000000000000..5f52edda8951
>> --- /dev/null
>> +++ b/Documentation/adding-syscalls.txt

[snip]

>> + - If there is an existing capability that governs related functionality, then
>> +   use that.  However, avoid combining lots of only vaguely related functions
>> +   together under the same bit, as this goes against capabilities' purpose of
>> +   splitting the power of root.  In particular, avoid adding new uses of the
>> +   already overly-general CAP_SYS_ADMIN capability.
>> + - If there is no related capability, then consider adding a new capability
>> +   bit -- but bear in mind that the numbering space is limited, and each new
>> +   bit needs to be understood and administered by sysadmins.
>
> Perhaps mention alternative mechanisms for access control when working
> on file descriptors, like avoiding security issues by looking at fd
> _opener_ credentials, rather than current's credentials?

I'm struggling to cope up with text about this that doesn't feel either
too vague or much too detailed / internal, so maybe I'm misunderstanding
what you're after.  Could you clarify or maybe suggest a sentence or two?

Thanks,
David
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/