Re: [f2fs-dev] [PATCH v3] f2fs: move ioctl interface definitions to separated file

[Jaegeuk Kim]

On 11/03, Chao Yu wrote:
> On 2020/11/3 11:22, Eric Biggers wrote:
> > On Mon, Nov 02, 2020 at 02:21:31PM +0800, Chao Yu wrote:
> > > +#define F2FS_IOC_MOVE_RANGE  _IOWR(F2FS_IOCTL_MAGIC, 9,  
> > > \
> > > + struct f2fs_move_range)
> > [...]
> > > +#define F2FS_IOC_GARBAGE_COLLECT_RANGE   _IOW(F2FS_IOCTL_MAGIC, 11,  
> > > \
> > > + struct f2fs_gc_range)
> > [...]
> > > +
> > > +struct f2fs_gc_range {
> > > + __u32 sync;
> > > + __u64 start;
> > > + __u64 len;
> > > +};
> > [...]
> > > +struct f2fs_move_range {
> > > + __u32 dst_fd;   /* destination fd */
> > > + __u64 pos_in;   /* start position in src_fd */
> > > + __u64 pos_out;  /* start position in dst_fd */
> > > + __u64 len;  /* size to move */
> > > +};
> > 
> > These two structs are weird because there is implicit padding between the 
> > __u32
> > field and the following __u64 field on some 32-bit architectures (e.g. 
> > x86_32)
> > but not others (e.g. arm32).
> > 
> > But f2fs_compat_ioctl() doesn't handle these two ioctls specially, but 
> > rather
> > just calls through to f2fs_ioctl().  That's wrong, and it means that
> > F2FS_IOC_MOVE_RANGE and F2FS_IOC_GARBAGE_COLLECT_RANGE won't work when 
> > called
> > from an x86_32 binary on an x86_64 kernel.
> 
> Nice catch!
> 
> > 
> > So something needs to be fixed.  I wonder if it's safe to just explicitly 
> > add
> > the padding field after the fact.  If no one is actually using these two 
> > ioctls
> > in a case where both userspace and the kernel lack the implicit padding 
> > (e.g.,
> > x86_32 userspace with x86_32 kernel), it should be fine...
> 
> IIRC, Jaegeuk added those interfaces, I hope it's not the requirement from 
> other
> f2fs userspace developers...if it is, there may be users.
> 
> I found one patch in ext4 which fixes the similar issue, I guess we can fix 
> this
> with the same way, thoughts?

Agreed. Please fix along with f2fs-tools/f2fs_io.

> 
> commit 4d92dc0f00a775dc2e1267b0e00befb783902fe7
> Author: Ben Hutchings 
> Date:   Mon May 17 06:00:00 2010 -0400
> 
> ext4: Fix compat EXT4_IOC_ADD_GROUP
> 
> struct ext4_new_group_input needs to be converted because u64 has
> only 32-bit alignment on some 32-bit architectures, notably i386.
> 
> Thanks,
> 
> > 
> > - Eric
> > .
> > 

Re: [f2fs-dev] [PATCH v3] f2fs: move ioctl interface definitions to separated file

[Chao Yu]

On 2020/11/3 11:22, Eric Biggers wrote:

On Mon, Nov 02, 2020 at 02:21:31PM +0800, Chao Yu wrote:

+#define F2FS_IOC_MOVE_RANGE_IOWR(F2FS_IOCTL_MAGIC, 9,  \
+   struct f2fs_move_range)

[...]

+#define F2FS_IOC_GARBAGE_COLLECT_RANGE _IOW(F2FS_IOCTL_MAGIC, 11,  \
+   struct f2fs_gc_range)

[...]

+
+struct f2fs_gc_range {
+   __u32 sync;
+   __u64 start;
+   __u64 len;
+};

[...]

+struct f2fs_move_range {
+   __u32 dst_fd;   /* destination fd */
+   __u64 pos_in;   /* start position in src_fd */
+   __u64 pos_out;  /* start position in dst_fd */
+   __u64 len;  /* size to move */
+};


These two structs are weird because there is implicit padding between the __u32
field and the following __u64 field on some 32-bit architectures (e.g. x86_32)
but not others (e.g. arm32).

But f2fs_compat_ioctl() doesn't handle these two ioctls specially, but rather
just calls through to f2fs_ioctl().  That's wrong, and it means that
F2FS_IOC_MOVE_RANGE and F2FS_IOC_GARBAGE_COLLECT_RANGE won't work when called
from an x86_32 binary on an x86_64 kernel.


Nice catch!



So something needs to be fixed.  I wonder if it's safe to just explicitly add
the padding field after the fact.  If no one is actually using these two ioctls
in a case where both userspace and the kernel lack the implicit padding (e.g.,
x86_32 userspace with x86_32 kernel), it should be fine...


IIRC, Jaegeuk added those interfaces, I hope it's not the requirement from other
f2fs userspace developers...if it is, there may be users.

I found one patch in ext4 which fixes the similar issue, I guess we can fix this
with the same way, thoughts?

commit 4d92dc0f00a775dc2e1267b0e00befb783902fe7
Author: Ben Hutchings 
Date:   Mon May 17 06:00:00 2010 -0400

ext4: Fix compat EXT4_IOC_ADD_GROUP

struct ext4_new_group_input needs to be converted because u64 has
only 32-bit alignment on some 32-bit architectures, notably i386.

Thanks,



- Eric
.

Re: [f2fs-dev] [PATCH v3] f2fs: move ioctl interface definitions to separated file

[Eric Biggers]

On Mon, Nov 02, 2020 at 02:21:31PM +0800, Chao Yu wrote:
> +#define F2FS_IOC_MOVE_RANGE  _IOWR(F2FS_IOCTL_MAGIC, 9,  \
> + struct f2fs_move_range)
[...]
> +#define F2FS_IOC_GARBAGE_COLLECT_RANGE   _IOW(F2FS_IOCTL_MAGIC, 11,  
> \
> + struct f2fs_gc_range)
[...]
> +
> +struct f2fs_gc_range {
> + __u32 sync;
> + __u64 start;
> + __u64 len;
> +};
[...]
> +struct f2fs_move_range {
> + __u32 dst_fd;   /* destination fd */
> + __u64 pos_in;   /* start position in src_fd */
> + __u64 pos_out;  /* start position in dst_fd */
> + __u64 len;  /* size to move */
> +};

These two structs are weird because there is implicit padding between the __u32
field and the following __u64 field on some 32-bit architectures (e.g. x86_32)
but not others (e.g. arm32).

But f2fs_compat_ioctl() doesn't handle these two ioctls specially, but rather
just calls through to f2fs_ioctl().  That's wrong, and it means that
F2FS_IOC_MOVE_RANGE and F2FS_IOC_GARBAGE_COLLECT_RANGE won't work when called
from an x86_32 binary on an x86_64 kernel.

So something needs to be fixed.  I wonder if it's safe to just explicitly add
the padding field after the fact.  If no one is actually using these two ioctls
in a case where both userspace and the kernel lack the implicit padding (e.g.,
x86_32 userspace with x86_32 kernel), it should be fine...

- Eric