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[next] UAPI: nfsfh.h: Replace one-element array with flexible-array member

Message ID 20210323224858.GA293698@embeddedor (mailing list archive)
State New
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Series [next] UAPI: nfsfh.h: Replace one-element array with flexible-array member | expand

Commit Message

Gustavo A. R. Silva March 23, 2021, 10:48 p.m. UTC
There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

Use an anonymous union with a couple of anonymous structs in order to
keep userspace unchanged:

$ pahole -C nfs_fhbase_new fs/nfsd/nfsfh.o
struct nfs_fhbase_new {
        union {
                struct {
                        __u8       fb_version_aux;       /*     0     1 */
                        __u8       fb_auth_type_aux;     /*     1     1 */
                        __u8       fb_fsid_type_aux;     /*     2     1 */
                        __u8       fb_fileid_type_aux;   /*     3     1 */
                        __u32      fb_auth[1];           /*     4     4 */
                };                                       /*     0     8 */
                struct {
                        __u8       fb_version;           /*     0     1 */
                        __u8       fb_auth_type;         /*     1     1 */
                        __u8       fb_fsid_type;         /*     2     1 */
                        __u8       fb_fileid_type;       /*     3     1 */
                        __u32      fb_auth_flex[0];      /*     4     0 */
                };                                       /*     0     4 */
        };                                               /*     0     8 */

        /* size: 8, cachelines: 1, members: 1 */
        /* last cacheline: 8 bytes */
};

Also, this helps with the ongoing efforts to enable -Warray-bounds by
fixing the following warnings:

fs/nfsd/nfsfh.c: In function ‘nfsd_set_fh_dentry’:
fs/nfsd/nfsfh.c:191:41: warning: array subscript 1 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
  191 |        ntohl((__force __be32)fh->fh_fsid[1])));
      |                              ~~~~~~~~~~~^~~
./include/linux/kdev_t.h:12:46: note: in definition of macro ‘MKDEV’
   12 | #define MKDEV(ma,mi) (((ma) << MINORBITS) | (mi))
      |                                              ^~
./include/uapi/linux/byteorder/little_endian.h:40:26: note: in expansion of macro ‘__swab32’
   40 | #define __be32_to_cpu(x) __swab32((__force __u32)(__be32)(x))
      |                          ^~~~~~~~
./include/linux/byteorder/generic.h:136:21: note: in expansion of macro ‘__be32_to_cpu’
  136 | #define ___ntohl(x) __be32_to_cpu(x)
      |                     ^~~~~~~~~~~~~
./include/linux/byteorder/generic.h:140:18: note: in expansion of macro ‘___ntohl’
  140 | #define ntohl(x) ___ntohl(x)
      |                  ^~~~~~~~
fs/nfsd/nfsfh.c:191:8: note: in expansion of macro ‘ntohl’
  191 |        ntohl((__force __be32)fh->fh_fsid[1])));
      |        ^~~~~
fs/nfsd/nfsfh.c:192:32: warning: array subscript 2 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
  192 |    fh->fh_fsid[1] = fh->fh_fsid[2];
      |                     ~~~~~~~~~~~^~~
fs/nfsd/nfsfh.c:192:15: warning: array subscript 1 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
  192 |    fh->fh_fsid[1] = fh->fh_fsid[2];
      |    ~~~~~~~~~~~^~~

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 include/uapi/linux/nfsd/nfsfh.h | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

Comments

Gustavo A. R. Silva March 25, 2021, 1:18 p.m. UTC | #1
On 3/25/21 08:45, David Laight wrote:
> From: Gustavo A. R. Silva
>> Sent: 23 March 2021 22:49
>>
>> There is a regular need in the kernel to provide a way to declare having
>> a dynamically sized set of trailing elements in a structure. Kernel code
>> should always use “flexible array members”[1] for these cases. The older
>> style of one-element or zero-length arrays should no longer be used[2].
>>
>> Use an anonymous union with a couple of anonymous structs in order to
>> keep userspace unchanged:
>>
>> $ pahole -C nfs_fhbase_new fs/nfsd/nfsfh.o
>> struct nfs_fhbase_new {
>>         union {
>>                 struct {
>>                         __u8       fb_version_aux;       /*     0     1 */
>>                         __u8       fb_auth_type_aux;     /*     1     1 */
>>                         __u8       fb_fsid_type_aux;     /*     2     1 */
>>                         __u8       fb_fileid_type_aux;   /*     3     1 */
>>                         __u32      fb_auth[1];           /*     4     4 */
>>                 };                                       /*     0     8 */
>>                 struct {
>>                         __u8       fb_version;           /*     0     1 */
>>                         __u8       fb_auth_type;         /*     1     1 */
>>                         __u8       fb_fsid_type;         /*     2     1 */
>>                         __u8       fb_fileid_type;       /*     3     1 */
>>                         __u32      fb_auth_flex[0];      /*     4     0 */
>>                 };                                       /*     0     4 */
>>         };                                               /*     0     8 */
>>
>>         /* size: 8, cachelines: 1, members: 1 */
>>         /* last cacheline: 8 bytes */
>> };
> 
> Could you use the simpler:
>> struct nfs_fhbase_new {
>>          __u8       fb_version;
>>          __u8       fb_auth_type;
>>          __u8       fb_fsid_type;
>>          __u8       fb_fileid_type;
>>          union {
>>                 __u32      fb_auth[1];
>>                 __u32      fb_auth_flex[0];
>>          };
>> };
> 
> Although I'm not certain flexible arrays are supported
> as the last element of a union.

Nope; this is not allowed: https://godbolt.org/z/14vd4o8na

--
Gustavo
David Laight March 25, 2021, 1:45 p.m. UTC | #2
From: Gustavo A. R. Silva
> Sent: 23 March 2021 22:49
> 
> There is a regular need in the kernel to provide a way to declare having
> a dynamically sized set of trailing elements in a structure. Kernel code
> should always use “flexible array members”[1] for these cases. The older
> style of one-element or zero-length arrays should no longer be used[2].
> 
> Use an anonymous union with a couple of anonymous structs in order to
> keep userspace unchanged:
> 
> $ pahole -C nfs_fhbase_new fs/nfsd/nfsfh.o
> struct nfs_fhbase_new {
>         union {
>                 struct {
>                         __u8       fb_version_aux;       /*     0     1 */
>                         __u8       fb_auth_type_aux;     /*     1     1 */
>                         __u8       fb_fsid_type_aux;     /*     2     1 */
>                         __u8       fb_fileid_type_aux;   /*     3     1 */
>                         __u32      fb_auth[1];           /*     4     4 */
>                 };                                       /*     0     8 */
>                 struct {
>                         __u8       fb_version;           /*     0     1 */
>                         __u8       fb_auth_type;         /*     1     1 */
>                         __u8       fb_fsid_type;         /*     2     1 */
>                         __u8       fb_fileid_type;       /*     3     1 */
>                         __u32      fb_auth_flex[0];      /*     4     0 */
>                 };                                       /*     0     4 */
>         };                                               /*     0     8 */
> 
>         /* size: 8, cachelines: 1, members: 1 */
>         /* last cacheline: 8 bytes */
> };

Could you use the simpler:
> struct nfs_fhbase_new {
>          __u8       fb_version;
>          __u8       fb_auth_type;
>          __u8       fb_fsid_type;
>          __u8       fb_fileid_type;
>          union {
>                 __u32      fb_auth[1];
>                 __u32      fb_auth_flex[0];
>          };
> };

Although I'm not certain flexible arrays are supported
as the last element of a union.
You might need to use a named anonymous structure for the
four __u8 fields and create two different structures that
include the extra field on the end.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
David Laight March 25, 2021, 3:29 p.m. UTC | #3
From: Gustavo A. R. Silva
> Sent: 25 March 2021 13:18
> 
> On 3/25/21 08:45, David Laight wrote:
> > From: Gustavo A. R. Silva
> >> Sent: 23 March 2021 22:49
> >>
> >> There is a regular need in the kernel to provide a way to declare having
> >> a dynamically sized set of trailing elements in a structure. Kernel code
> >> should always use “flexible array members”[1] for these cases. The older
> >> style of one-element or zero-length arrays should no longer be used[2].
> >>
> >> Use an anonymous union with a couple of anonymous structs in order to
> >> keep userspace unchanged:
> >>
> >> $ pahole -C nfs_fhbase_new fs/nfsd/nfsfh.o
> >> struct nfs_fhbase_new {
> >>         union {
> >>                 struct {
> >>                         __u8       fb_version_aux;       /*     0     1 */
> >>                         __u8       fb_auth_type_aux;     /*     1     1 */
> >>                         __u8       fb_fsid_type_aux;     /*     2     1 */
> >>                         __u8       fb_fileid_type_aux;   /*     3     1 */
> >>                         __u32      fb_auth[1];           /*     4     4 */
> >>                 };                                       /*     0     8 */
> >>                 struct {
> >>                         __u8       fb_version;           /*     0     1 */
> >>                         __u8       fb_auth_type;         /*     1     1 */
> >>                         __u8       fb_fsid_type;         /*     2     1 */
> >>                         __u8       fb_fileid_type;       /*     3     1 */
> >>                         __u32      fb_auth_flex[0];      /*     4     0 */
> >>                 };                                       /*     0     4 */
> >>         };                                               /*     0     8 */
> >>
> >>         /* size: 8, cachelines: 1, members: 1 */
> >>         /* last cacheline: 8 bytes */
> >> };
> >
> > Could you use the simpler:
> >> struct nfs_fhbase_new {
> >>          __u8       fb_version;
> >>          __u8       fb_auth_type;
> >>          __u8       fb_fsid_type;
> >>          __u8       fb_fileid_type;
> >>          union {
> >>                 __u32      fb_auth[1];
> >>                 __u32      fb_auth_flex[0];
> >>          };
> >> };
> >
> > Although I'm not certain flexible arrays are supported
> > as the last element of a union.
> 
> Nope; this is not allowed: https://godbolt.org/z/14vd4o8na

Nothing an extra 'struct {__u32 fb_auth_flex[0]; }'; won't solve.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
Gustavo A. R. Silva March 25, 2021, 9:12 p.m. UTC | #4
On 3/25/21 10:29, David Laight wrote:

>>>
>>> Could you use the simpler:
>>>> struct nfs_fhbase_new {
>>>>          __u8       fb_version;
>>>>          __u8       fb_auth_type;
>>>>          __u8       fb_fsid_type;
>>>>          __u8       fb_fileid_type;
>>>>          union {
>>>>                 __u32      fb_auth[1];
>>>>                 __u32      fb_auth_flex[0];
>>>>          };
>>>> };
>>>
>>> Although I'm not certain flexible arrays are supported
>>> as the last element of a union.
>>
>> Nope; this is not allowed: https://godbolt.org/z/14vd4o8na
> 
> Nothing an extra 'struct {__u32 fb_auth_flex[0]; }'; won't solve.

We don't want to introduce zero-length arrays [1].

--
Gustavo

[1] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays
David Laight March 26, 2021, 8:17 a.m. UTC | #5
From: Gustavo A. R. Silva
> Sent: 25 March 2021 21:12
> 
> On 3/25/21 10:29, David Laight wrote:
> 
> >>>
> >>> Could you use the simpler:
> >>>> struct nfs_fhbase_new {
> >>>>          __u8       fb_version;
> >>>>          __u8       fb_auth_type;
> >>>>          __u8       fb_fsid_type;
> >>>>          __u8       fb_fileid_type;
> >>>>          union {
> >>>>                 __u32      fb_auth[1];
> >>>>                 __u32      fb_auth_flex[0];
> >>>>          };
> >>>> };
> >>>
> >>> Although I'm not certain flexible arrays are supported
> >>> as the last element of a union.
> >>
> >> Nope; this is not allowed: https://godbolt.org/z/14vd4o8na
> >
> > Nothing an extra 'struct {__u32 fb_auth_flex[0]; }'; won't solve.
> 
> We don't want to introduce zero-length arrays [1].

I probably meant to write [] not [0] - doesn't affect the idea.

The real problem is that the compiler is likely to start rejecting
references to a flex array that go beyond the end of the outer
structure.

Thinking back, isn't fb_auth[] at least one entry long?
So it could be:

struct nfs_fhbase_new {
         __u8       fb_version;
         __u8       fb_auth_type;
         __u8       fb_fsid_type;
         __u8       fb_fileid_type;
         __u32      fb_auth[1];
         __u32      fb_auth_extra[];
};

(I've missed the 0 out this time...)

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
Gustavo A. R. Silva March 26, 2021, 2:10 p.m. UTC | #6
On 3/26/21 03:17, David Laight wrote:
> From: Gustavo A. R. Silva
>> Sent: 25 March 2021 21:12
>>
>> On 3/25/21 10:29, David Laight wrote:
>>
>>>>>
>>>>> Could you use the simpler:
>>>>>> struct nfs_fhbase_new {
>>>>>>          __u8       fb_version;
>>>>>>          __u8       fb_auth_type;
>>>>>>          __u8       fb_fsid_type;
>>>>>>          __u8       fb_fileid_type;
>>>>>>          union {
>>>>>>                 __u32      fb_auth[1];
>>>>>>                 __u32      fb_auth_flex[0];
>>>>>>          };
>>>>>> };
>>>>>
>>>>> Although I'm not certain flexible arrays are supported
>>>>> as the last element of a union.
>>>>
>>>> Nope; this is not allowed: https://godbolt.org/z/14vd4o8na
>>>
>>> Nothing an extra 'struct {__u32 fb_auth_flex[0]; }'; won't solve.
>>
>> We don't want to introduce zero-length arrays [1].
> 
> I probably meant to write [] not [0] - doesn't affect the idea.
> 
> The real problem is that the compiler is likely to start rejecting
> references to a flex array that go beyond the end of the outer
> structure.
> 
> Thinking back, isn't fb_auth[] at least one entry long?
> So it could be:
> 
> struct nfs_fhbase_new {
>          __u8       fb_version;
>          __u8       fb_auth_type;
>          __u8       fb_fsid_type;
>          __u8       fb_fileid_type;
>          __u32      fb_auth[1];
>          __u32      fb_auth_extra[];
> };

I don't think this is a great idea because, contrary to the change I'm
proposing, in this case memory regions for fb_auth and fb_auth_extra
don't actually overlap.

--
Gustavo
Gustavo A. R. Silva March 29, 2021, 2:51 p.m. UTC | #7
On 3/29/21 09:57, Chuck Lever wrote:
> Sorry for the reply via gmail, the original patch did not show up in
> my Oracle mailbox.
> 
> I've been waiting for a resolution of this thread (and perhaps a
> Reviewed-by). But in
> the meantime I've committed this, provisionally, to the for-next topic branch in
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git

Awesome. :)

Thanks, Chuck.
--
Gustavo

> On Wed, Mar 24, 2021 at 4:39 AM Gustavo A. R. Silva
> <gustavoars@kernel.org> wrote:
>>
>> There is a regular need in the kernel to provide a way to declare having
>> a dynamically sized set of trailing elements in a structure. Kernel code
>> should always use “flexible array members”[1] for these cases. The older
>> style of one-element or zero-length arrays should no longer be used[2].
>>
>> Use an anonymous union with a couple of anonymous structs in order to
>> keep userspace unchanged:
>>
>> $ pahole -C nfs_fhbase_new fs/nfsd/nfsfh.o
>> struct nfs_fhbase_new {
>>         union {
>>                 struct {
>>                         __u8       fb_version_aux;       /*     0     1 */
>>                         __u8       fb_auth_type_aux;     /*     1     1 */
>>                         __u8       fb_fsid_type_aux;     /*     2     1 */
>>                         __u8       fb_fileid_type_aux;   /*     3     1 */
>>                         __u32      fb_auth[1];           /*     4     4 */
>>                 };                                       /*     0     8 */
>>                 struct {
>>                         __u8       fb_version;           /*     0     1 */
>>                         __u8       fb_auth_type;         /*     1     1 */
>>                         __u8       fb_fsid_type;         /*     2     1 */
>>                         __u8       fb_fileid_type;       /*     3     1 */
>>                         __u32      fb_auth_flex[0];      /*     4     0 */
>>                 };                                       /*     0     4 */
>>         };                                               /*     0     8 */
>>
>>         /* size: 8, cachelines: 1, members: 1 */
>>         /* last cacheline: 8 bytes */
>> };
>>
>> Also, this helps with the ongoing efforts to enable -Warray-bounds by
>> fixing the following warnings:
>>
>> fs/nfsd/nfsfh.c: In function ‘nfsd_set_fh_dentry’:
>> fs/nfsd/nfsfh.c:191:41: warning: array subscript 1 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
>>   191 |        ntohl((__force __be32)fh->fh_fsid[1])));
>>       |                              ~~~~~~~~~~~^~~
>> ./include/linux/kdev_t.h:12:46: note: in definition of macro ‘MKDEV’
>>    12 | #define MKDEV(ma,mi) (((ma) << MINORBITS) | (mi))
>>       |                                              ^~
>> ./include/uapi/linux/byteorder/little_endian.h:40:26: note: in expansion of macro ‘__swab32’
>>    40 | #define __be32_to_cpu(x) __swab32((__force __u32)(__be32)(x))
>>       |                          ^~~~~~~~
>> ./include/linux/byteorder/generic.h:136:21: note: in expansion of macro ‘__be32_to_cpu’
>>   136 | #define ___ntohl(x) __be32_to_cpu(x)
>>       |                     ^~~~~~~~~~~~~
>> ./include/linux/byteorder/generic.h:140:18: note: in expansion of macro ‘___ntohl’
>>   140 | #define ntohl(x) ___ntohl(x)
>>       |                  ^~~~~~~~
>> fs/nfsd/nfsfh.c:191:8: note: in expansion of macro ‘ntohl’
>>   191 |        ntohl((__force __be32)fh->fh_fsid[1])));
>>       |        ^~~~~
>> fs/nfsd/nfsfh.c:192:32: warning: array subscript 2 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
>>   192 |    fh->fh_fsid[1] = fh->fh_fsid[2];
>>       |                     ~~~~~~~~~~~^~~
>> fs/nfsd/nfsfh.c:192:15: warning: array subscript 1 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
>>   192 |    fh->fh_fsid[1] = fh->fh_fsid[2];
>>       |    ~~~~~~~~~~~^~~
>>
>> [1] https://en.wikipedia.org/wiki/Flexible_array_member
>> [2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays
>>
>> Link: https://github.com/KSPP/linux/issues/79
>> Link: https://github.com/KSPP/linux/issues/109
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
>> ---
>>  include/uapi/linux/nfsd/nfsfh.h | 27 +++++++++++++++++++--------
>>  1 file changed, 19 insertions(+), 8 deletions(-)
>>
>> diff --git a/include/uapi/linux/nfsd/nfsfh.h b/include/uapi/linux/nfsd/nfsfh.h
>> index ff0ca88b1c8f..427294dd56a1 100644
>> --- a/include/uapi/linux/nfsd/nfsfh.h
>> +++ b/include/uapi/linux/nfsd/nfsfh.h
>> @@ -64,13 +64,24 @@ struct nfs_fhbase_old {
>>   *   in include/linux/exportfs.h for currently registered values.
>>   */
>>  struct nfs_fhbase_new {
>> -       __u8            fb_version;     /* == 1, even => nfs_fhbase_old */
>> -       __u8            fb_auth_type;
>> -       __u8            fb_fsid_type;
>> -       __u8            fb_fileid_type;
>> -       __u32           fb_auth[1];
>> -/*     __u32           fb_fsid[0]; floating */
>> -/*     __u32           fb_fileid[0]; floating */
>> +       union {
>> +               struct {
>> +                       __u8            fb_version_aux; /* == 1, even => nfs_fhbase_old */
>> +                       __u8            fb_auth_type_aux;
>> +                       __u8            fb_fsid_type_aux;
>> +                       __u8            fb_fileid_type_aux;
>> +                       __u32           fb_auth[1];
>> +                       /*      __u32           fb_fsid[0]; floating */
>> +                       /*      __u32           fb_fileid[0]; floating */
>> +               };
>> +               struct {
>> +                       __u8            fb_version;     /* == 1, even => nfs_fhbase_old */
>> +                       __u8            fb_auth_type;
>> +                       __u8            fb_fsid_type;
>> +                       __u8            fb_fileid_type;
>> +                       __u32           fb_auth_flex[]; /* flexible-array member */
>> +               };
>> +       };
>>  };
>>
>>  struct knfsd_fh {
>> @@ -97,7 +108,7 @@ struct knfsd_fh {
>>  #define        fh_fsid_type            fh_base.fh_new.fb_fsid_type
>>  #define        fh_auth_type            fh_base.fh_new.fb_auth_type
>>  #define        fh_fileid_type          fh_base.fh_new.fb_fileid_type
>> -#define        fh_fsid                 fh_base.fh_new.fb_auth
>> +#define        fh_fsid                 fh_base.fh_new.fb_auth_flex
>>
>>  /* Do not use, provided for userspace compatiblity. */
>>  #define        fh_auth                 fh_base.fh_new.fb_auth
>> --
>> 2.27.0
>>
> 
>
Chuck Lever III March 29, 2021, 2:57 p.m. UTC | #8
Sorry for the reply via gmail, the original patch did not show up in
my Oracle mailbox.

I've been waiting for a resolution of this thread (and perhaps a
Reviewed-by). But in
the meantime I've committed this, provisionally, to the for-next topic branch in

git://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git

On Wed, Mar 24, 2021 at 4:39 AM Gustavo A. R. Silva
<gustavoars@kernel.org> wrote:
>
> There is a regular need in the kernel to provide a way to declare having
> a dynamically sized set of trailing elements in a structure. Kernel code
> should always use “flexible array members”[1] for these cases. The older
> style of one-element or zero-length arrays should no longer be used[2].
>
> Use an anonymous union with a couple of anonymous structs in order to
> keep userspace unchanged:
>
> $ pahole -C nfs_fhbase_new fs/nfsd/nfsfh.o
> struct nfs_fhbase_new {
>         union {
>                 struct {
>                         __u8       fb_version_aux;       /*     0     1 */
>                         __u8       fb_auth_type_aux;     /*     1     1 */
>                         __u8       fb_fsid_type_aux;     /*     2     1 */
>                         __u8       fb_fileid_type_aux;   /*     3     1 */
>                         __u32      fb_auth[1];           /*     4     4 */
>                 };                                       /*     0     8 */
>                 struct {
>                         __u8       fb_version;           /*     0     1 */
>                         __u8       fb_auth_type;         /*     1     1 */
>                         __u8       fb_fsid_type;         /*     2     1 */
>                         __u8       fb_fileid_type;       /*     3     1 */
>                         __u32      fb_auth_flex[0];      /*     4     0 */
>                 };                                       /*     0     4 */
>         };                                               /*     0     8 */
>
>         /* size: 8, cachelines: 1, members: 1 */
>         /* last cacheline: 8 bytes */
> };
>
> Also, this helps with the ongoing efforts to enable -Warray-bounds by
> fixing the following warnings:
>
> fs/nfsd/nfsfh.c: In function ‘nfsd_set_fh_dentry’:
> fs/nfsd/nfsfh.c:191:41: warning: array subscript 1 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
>   191 |        ntohl((__force __be32)fh->fh_fsid[1])));
>       |                              ~~~~~~~~~~~^~~
> ./include/linux/kdev_t.h:12:46: note: in definition of macro ‘MKDEV’
>    12 | #define MKDEV(ma,mi) (((ma) << MINORBITS) | (mi))
>       |                                              ^~
> ./include/uapi/linux/byteorder/little_endian.h:40:26: note: in expansion of macro ‘__swab32’
>    40 | #define __be32_to_cpu(x) __swab32((__force __u32)(__be32)(x))
>       |                          ^~~~~~~~
> ./include/linux/byteorder/generic.h:136:21: note: in expansion of macro ‘__be32_to_cpu’
>   136 | #define ___ntohl(x) __be32_to_cpu(x)
>       |                     ^~~~~~~~~~~~~
> ./include/linux/byteorder/generic.h:140:18: note: in expansion of macro ‘___ntohl’
>   140 | #define ntohl(x) ___ntohl(x)
>       |                  ^~~~~~~~
> fs/nfsd/nfsfh.c:191:8: note: in expansion of macro ‘ntohl’
>   191 |        ntohl((__force __be32)fh->fh_fsid[1])));
>       |        ^~~~~
> fs/nfsd/nfsfh.c:192:32: warning: array subscript 2 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
>   192 |    fh->fh_fsid[1] = fh->fh_fsid[2];
>       |                     ~~~~~~~~~~~^~~
> fs/nfsd/nfsfh.c:192:15: warning: array subscript 1 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds]
>   192 |    fh->fh_fsid[1] = fh->fh_fsid[2];
>       |    ~~~~~~~~~~~^~~
>
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays
>
> Link: https://github.com/KSPP/linux/issues/79
> Link: https://github.com/KSPP/linux/issues/109
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
>  include/uapi/linux/nfsd/nfsfh.h | 27 +++++++++++++++++++--------
>  1 file changed, 19 insertions(+), 8 deletions(-)
>
> diff --git a/include/uapi/linux/nfsd/nfsfh.h b/include/uapi/linux/nfsd/nfsfh.h
> index ff0ca88b1c8f..427294dd56a1 100644
> --- a/include/uapi/linux/nfsd/nfsfh.h
> +++ b/include/uapi/linux/nfsd/nfsfh.h
> @@ -64,13 +64,24 @@ struct nfs_fhbase_old {
>   *   in include/linux/exportfs.h for currently registered values.
>   */
>  struct nfs_fhbase_new {
> -       __u8            fb_version;     /* == 1, even => nfs_fhbase_old */
> -       __u8            fb_auth_type;
> -       __u8            fb_fsid_type;
> -       __u8            fb_fileid_type;
> -       __u32           fb_auth[1];
> -/*     __u32           fb_fsid[0]; floating */
> -/*     __u32           fb_fileid[0]; floating */
> +       union {
> +               struct {
> +                       __u8            fb_version_aux; /* == 1, even => nfs_fhbase_old */
> +                       __u8            fb_auth_type_aux;
> +                       __u8            fb_fsid_type_aux;
> +                       __u8            fb_fileid_type_aux;
> +                       __u32           fb_auth[1];
> +                       /*      __u32           fb_fsid[0]; floating */
> +                       /*      __u32           fb_fileid[0]; floating */
> +               };
> +               struct {
> +                       __u8            fb_version;     /* == 1, even => nfs_fhbase_old */
> +                       __u8            fb_auth_type;
> +                       __u8            fb_fsid_type;
> +                       __u8            fb_fileid_type;
> +                       __u32           fb_auth_flex[]; /* flexible-array member */
> +               };
> +       };
>  };
>
>  struct knfsd_fh {
> @@ -97,7 +108,7 @@ struct knfsd_fh {
>  #define        fh_fsid_type            fh_base.fh_new.fb_fsid_type
>  #define        fh_auth_type            fh_base.fh_new.fb_auth_type
>  #define        fh_fileid_type          fh_base.fh_new.fb_fileid_type
> -#define        fh_fsid                 fh_base.fh_new.fb_auth
> +#define        fh_fsid                 fh_base.fh_new.fb_auth_flex
>
>  /* Do not use, provided for userspace compatiblity. */
>  #define        fh_auth                 fh_base.fh_new.fb_auth
> --
> 2.27.0
>
diff mbox series

Patch

diff --git a/include/uapi/linux/nfsd/nfsfh.h b/include/uapi/linux/nfsd/nfsfh.h
index ff0ca88b1c8f..427294dd56a1 100644
--- a/include/uapi/linux/nfsd/nfsfh.h
+++ b/include/uapi/linux/nfsd/nfsfh.h
@@ -64,13 +64,24 @@  struct nfs_fhbase_old {
  *   in include/linux/exportfs.h for currently registered values.
  */
 struct nfs_fhbase_new {
-	__u8		fb_version;	/* == 1, even => nfs_fhbase_old */
-	__u8		fb_auth_type;
-	__u8		fb_fsid_type;
-	__u8		fb_fileid_type;
-	__u32		fb_auth[1];
-/*	__u32		fb_fsid[0]; floating */
-/*	__u32		fb_fileid[0]; floating */
+	union {
+		struct {
+			__u8		fb_version_aux;	/* == 1, even => nfs_fhbase_old */
+			__u8		fb_auth_type_aux;
+			__u8		fb_fsid_type_aux;
+			__u8		fb_fileid_type_aux;
+			__u32		fb_auth[1];
+			/*	__u32		fb_fsid[0]; floating */
+			/*	__u32		fb_fileid[0]; floating */
+		};
+		struct {
+			__u8		fb_version;	/* == 1, even => nfs_fhbase_old */
+			__u8		fb_auth_type;
+			__u8		fb_fsid_type;
+			__u8		fb_fileid_type;
+			__u32		fb_auth_flex[]; /* flexible-array member */
+		};
+	};
 };
 
 struct knfsd_fh {
@@ -97,7 +108,7 @@  struct knfsd_fh {
 #define	fh_fsid_type		fh_base.fh_new.fb_fsid_type
 #define	fh_auth_type		fh_base.fh_new.fb_auth_type
 #define	fh_fileid_type		fh_base.fh_new.fb_fileid_type
-#define	fh_fsid			fh_base.fh_new.fb_auth
+#define	fh_fsid			fh_base.fh_new.fb_auth_flex
 
 /* Do not use, provided for userspace compatiblity. */
 #define	fh_auth			fh_base.fh_new.fb_auth