Re: [f2fs-dev] [PATCH RFC] f2fs: fix compat F2FS_IOC_{MOVE, GARBAGE_COLLECT}_RANGE

[Chao Yu]

On 2020/11/4 10:29, Eric Biggers wrote:
> On Wed, Nov 04, 2020 at 10:19:06AM +0800, Chao Yu wrote:
> > Eric reported a ioctl bug in below link:
> >
> > https://lore.kernel.org/linux-f2fs-devel/20201103032234.GB2875@sol.localdomain/
> >
> > That said, on some 32-bit architectures, u64 has only 32-bit alignment,
> > notably i386 and x86_32, so that size of struct f2fs_gc_range compiled
> > in x86_32 is 20 bytes, however the size in x86_64 is 24 bytes, binary
> > compiled in x86_32 can not call F2FS_IOC_GARBAGE_COLLECT_RANGE successfully
> > due to mismatched value of ioctl command in betweeen binary and f2fs
> > module, similarly, F2FS_IOC_MOVE_RANGE will fail too.
> >
> > In this patch we introduce two ioctls for compatibility of above special
> > 32-bit binary:
> > - F2FS_IOC32_GARBAGE_COLLECT_RANGE
> > - F2FS_IOC32_MOVE_RANGE
> >
> > Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
> > ---
> >
> > Jaegeuk, Eric,
> >
> > I have no 32-bit machine now, so I don't run any test on this patch,
> > please take a look at this RFC patch first.
>
> You can test this by running a 32-bit binary on a machine with a 64-bit kernel.
> E.g. on x86_64, compile a binary with 'gcc -m32'.

Ah, thanks for providing the option, I can try that.

> >   #ifdef CONFIG_COMPAT
> > +static int f2fs_compat_ioc_gc_range(struct file *file, unsigned long arg)
> > +{
> > +	struct compat_f2fs_gc_range __user *urange;
> > +	struct f2fs_gc_range range;
> > +	int err;
> > +
> > +	urange = compat_ptr(arg);
> > +	err = get_user(range.sync, &urange->sync);
> > +	err |= get_user(range.start, &urange->start);
> > +	err |= get_user(range.len, &urange->len);
> > +	if (err)
> > +		return -EFAULT;
> > +	if (unlikely(f2fs_cp_error(F2FS_I_SB(file_inode(file)))))
> > +		return -EIO;
> > +	if (!f2fs_is_checkpoint_ready(F2FS_I_SB(file_inode(file))))
> > +		return -ENOSPC;
> > +	return f2fs_ioc_gc_range(file, (unsigned long)&range);
> > +}
>
> This won't work because f2fs_ioc_gc_range() expects a user pointer.  You'll need
> to make the native and compat versions do the copy from user separately, and
> have them call a helper function that takes a pointer to the argument in kernel
> memory.

Yes, I need to introduce function like __f2fs_ioc_gc_range() to accepted pointer
parameter which points kernel memory.

Will do test and resend v2 soon.

Thanks,

> - Eric
> .