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SubjectRe: [PATCH] vfs: fix statfs64() returning impossible EOVERFLOW for 64-bit f_files
On Mon, Aug 06, 2018 at 11:45:29AM -0700, Linus Torvalds wrote:
> On Mon, Aug 6, 2018 at 10:06 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > That leaves us with f_bsize and f_frsize (the latter defaulting to the former).
> > Hugetlbfs can put greater than 4Gb values in there, for really huge pages.
> > And that's the only thing worth checking in there.
> >
> > So the whole put_compat_statfs64() thing should be
>
> Ack, I'm ok with this simplification.
>
> > I'm somewhat tempted to get rid of those 'long' in struct kstatfs,
>
> I'm ok with this one too.
>
> > with
> >
> > #define STATFS_COPYOUT(type) \
> > static int put##type(struct kstatfs *st, struct type __user *p) \
>
> No. Don't do this.
>
> I'm ok with the #define to avoid duplication, but don't bother with
> the FIT_IN() after you've above successfully argued that it's
> pointless for anything but f_bsize/frsize.
>
> So if you do the macro to generate the different copyout versions,
> just use your simplified code for that macro instead. With FIT_IN()
> just for f_bsize/frsize.

For statfs64 (both native and compat) that would do nicely; for statfs,
however... The following describes the field sizes in all that mess:

kstatfs statfs statfs64 compat_statfs compat_statfs64
!s390 s390 !s390 s390
type: W W 32 W 32 32 32
namelen:W W 32 W 32 32 32
flags: W W 32 W 32 32 32
bsize: W W 32 W 32 32 32
frsize: W W 32 W 32 32 32
blocks: 64 W 64 64 64 32 64
bfree: 64 W 64 64 64 32 64
bavail: 64 W 64 64 64 32 64
files: 64 W 64 64 64 32 64
ffree: 64 W 64 64 64 32 64
fsid: __kernel_fsid_t on all

First of all, nobody gives a fuck about type, namelen and flags
overflows - can't happen.

blocks/bfree/bavail/files/ffree: can overflow in plain statfs on 32bit
and in compat statfs. For files/ffree we also have "-1 means (s32)-1,
not an overflow" there.

bsize/frsize: can oveflow in anything on s390 or mips64 and any compat on anything

Oh, and then there's signedness - in compat_statfs64 everything's unsigned,
but for compat_statfs a bunch of those 32bit ones are signed. Native on
32bit tend to be unsigned; native on 64bit and compat are often signed.
IMO that's a bug - compat ones should all be same as native 32bit.
As it is,
arm, parisc, ppc, sparc, x86: on 32bit - unsigned, compat on 64bit - signed
mips: both signed
s390: both unsigned
I think we want to switch compat_statfs fields on the first group to u32. These
declarations are not exposed to userland anyway. mips is interesting - I've no
idea how does mips32 userland react to e.g. statfs() on 3G block filesystem...

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