Hi Petro,
The read permission is needed even when you just want to open a file:
$ vim noreadfile
$ chmod 0000 noreadfile
$ ls -l noreadfile
---------- 1 user user 5 jan 28 09:24 noreadfile
$ cat noreadfile
cat: noreadfile: Permission denied
You can even try to create a C program just to open it, and it will fail.
See the man page of open function:
The argument flags *must* include one of the following access
modes: O_RDONLY, O_WRONLY, or
O_RDWR. These request opening the file read-only, write-only,
or read/write, respectively.
This man page makes it clear you must include an access mode, but I
passed 0 to the access mode flag of open() and it was accepted, but
when the file has permission 0000 it returns -EPERM: "Failed to open
file: error -1"
BR,
Alan
On 1/28/22, Petro Karashchenko <petro.karashche...@gmail.com> wrote:
> Hello,
>
> Yes, but how does this relate to "0000" mode for "register_driver()"?
> Maybe you can describe some use case so it will become more clear?
> Currently ioctl works fine if driver is registered with "0000" permission
> mode.
>
> Best regards,
> Petro
>
> пт, 28 січ. 2022 р. о 11:39 Xiang Xiao <xiaoxiang781...@gmail.com> пише:
>>
>> If we want to do the correct permission check, the ioctl handler needs to
>> check R/W bit by itself based on how the ioctl is implemented.
>> Or follow up how Linux encode the needed permission into each IOCTL:
>> https://github.com/torvalds/linux/blob/master/include/uapi/asm-generic/ioctl.h#L85-L91
>> and let's VFS layer do the check for each driver.
>>
>> On Fri, Jan 28, 2022 at 5:14 PM Petro Karashchenko <
>> petro.karashche...@gmail.com> wrote:
>>
>> > Hello team,
>> >
>> > Recently I have noticed that there are many places in code where
>> > register_driver() is called with non-zero mode with file operation
>> > structures that have neither read nor write APIs implemented. For
>> > example "ret = register_driver(path, &opamp_fops, 0444, dev);" while
>> > opamp_fops has only "opamp_open", "opamp_close" and "opamp_ioctl"
>> > implemented. I made a PR to fix it
>> > https://github.com/apache/incubator-nuttx/pull/5347 and change mode
>> > from "0444" to "0000", but want to ask if anyone sees any drawback in
>> > such an approach? Maybe I'm missing something?
>> >
>> > Best regards,
>> > Petro
>> >
>
