linux-kernel - Re: [PATCH] fuse: Add ioctl flag for compat ioctl with 64-bit time

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Message-ID: <d2bab6ae-0c52-5a6a-78e4-72a5f298a85f@mev.co.uk>
Date:   Tue, 23 Apr 2019 16:14:43 +0100
From:   Ian Abbott <abbotti@....co.uk>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fuse: Add ioctl flag for compat ioctl with 64-bit time_t

On 23/04/2019 13:55, Miklos Szeredi wrote:
> On Fri, Mar 1, 2019 at 6:08 PM Ian Abbott <abbotti@....co.uk> wrote:
>>
>> Currently, a CUSE server running on a 64-bit kernel can tell when an
>> ioctl request comes from a process running a 32-bit ABI, but cannot tell
>> whether the requesting process is using legacy IA32 emulation or x32
>> ABI, for example.  In particular, the server does not know the size of
>> the client process's `time_t` type.
>>
>> For 64-bit kernels, the `FUSE_IOCTL_COMPAT` and `FUSE_IOCTL_32BIT` flags
>> are currently set in the ioctl input request (`struct fuse_ioctl_in`
>> member `flags`) for a 32-bit requesting process.  This patch defines a
>> new flag `FUSE_IOCTL_COMPAT_64TIME` and sets it if the 32-bit requesting
>> process (running on a 64-bit kernel) uses a 64-bit `time_t` type.
> 
> Hi,
> 
> Thanks for the patch.
> 
> I think it should rather use in_x32_syscall() helper and follow that
> naming because there's apparently at least one example in xfs of a
> non-time_t related ioctl that varies between the x32 vs ia32.

Hi Miklos,

It is conceivable that COMPAT_USE_64BIT_TIME could be true for some 
other arch/ABI (although currently it is only ever set for x86/x32). 
Should it have separate flags for "compat 64-bit time" and "compat x32" 
(even though that is currently redundant)?

Kind regards,
Ian.

> 
> Thanks,
> Miklos
> 
>>
>> Signed-off-by: Ian Abbott <abbotti@....co.uk>
>> ---
>>   fs/fuse/file.c            | 5 ++++-
>>   include/uapi/linux/fuse.h | 2 ++
>>   2 files changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
>> index 06096b60f1df..9777e7a19889 100644
>> --- a/fs/fuse/file.c
>> +++ b/fs/fuse/file.c
>> @@ -2576,8 +2576,11 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
>>   #if BITS_PER_LONG == 32
>>          inarg.flags |= FUSE_IOCTL_32BIT;
>>   #else
>> -       if (flags & FUSE_IOCTL_COMPAT)
>> +       if (flags & FUSE_IOCTL_COMPAT) {
>>                  inarg.flags |= FUSE_IOCTL_32BIT;
>> +               if (COMPAT_USE_64BIT_TIME)
>> +                       inarg.flags |= FUSE_IOCTL_COMPAT_64TIME;
>> +       }
>>   #endif
>>
>>          /* assume all the iovs returned by client always fits in a page */
>> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
>> index 2ac598614a8f..1f4a71486601 100644
>> --- a/include/uapi/linux/fuse.h
>> +++ b/include/uapi/linux/fuse.h
>> @@ -335,6 +335,7 @@ struct fuse_file_lock {
>>    * FUSE_IOCTL_RETRY: retry with new iovecs
>>    * FUSE_IOCTL_32BIT: 32bit ioctl
>>    * FUSE_IOCTL_DIR: is a directory
>> + * FUSE_IOCTL_COMPAT_64TIME: 32bit compat ioctl with 64bit time_t
>>    *
>>    * FUSE_IOCTL_MAX_IOV: maximum of in_iovecs + out_iovecs
>>    */
>> @@ -343,6 +344,7 @@ struct fuse_file_lock {
>>   #define FUSE_IOCTL_RETRY       (1 << 2)
>>   #define FUSE_IOCTL_32BIT       (1 << 3)
>>   #define FUSE_IOCTL_DIR         (1 << 4)
>> +#define FUSE_IOCTL_COMPAT_64TIME (1 << 5)
>>
>>   #define FUSE_IOCTL_MAX_IOV     256
>>
>> --
>> 2.20.1
>>


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