The put_user(val,ptr) macro wants a pointer in the second parameter, but in
fat_ioctl_filldir() the d_name field references a whole "array of chars".
Usually the compiler automatically converts it and uses a pointer to that
array, but it's more clean to explicitly give the real pointer to where someting
is put, which is in this case the first character of the d_name[] array.
I noticed that issue while trying to optimize the parisc put_user() macro
and used an intermediate variable to store the pointer. In that case I
got this error:
In file included from include/linux/uaccess.h:11,
from include/linux/compat.h:17,
from fs/fat/dir.c:18:
fs/fat/dir.c: In function ‘fat_ioctl_filldir’:
fs/fat/dir.c:725:33: error: invalid initializer
725 | if (put_user(0, d2->d_name) || \
| ^~
include/asm/uaccess.h:152:33: note: in definition of macro ‘__put_user’
152 | __typeof__(ptr) __ptr = ptr; \
| ^~~
fs/fat/dir.c:759:1: note: in expansion of macro ‘FAT_IOCTL_FILLDIR_FUNC’
759 | FAT_IOCTL_FILLDIR_FUNC(fat_ioctl_filldir, __fat_dirent)
The patch below cleans it up.
Signed-off-by: Helge Deller <[email protected]>
diff --git a/fs/fat/dir.c b/fs/fat/dir.c
index c4a274285858..249825017da7 100644
--- a/fs/fat/dir.c
+++ b/fs/fat/dir.c
@@ -722,7 +722,7 @@ static int func(struct dir_context *ctx, const char *name, int name_len, \
if (name_len >= sizeof(d1->d_name)) \
name_len = sizeof(d1->d_name) - 1; \
\
- if (put_user(0, d2->d_name) || \
+ if (put_user(0, &d2->d_name[0]) || \
put_user(0, &d2->d_reclen) || \
copy_to_user(d1->d_name, name, name_len) || \
put_user(0, d1->d_name + name_len) || \
Helge Deller <[email protected]> writes:
> The put_user(val,ptr) macro wants a pointer in the second parameter, but in
> fat_ioctl_filldir() the d_name field references a whole "array of chars".
> Usually the compiler automatically converts it and uses a pointer to that
> array, but it's more clean to explicitly give the real pointer to where someting
> is put, which is in this case the first character of the d_name[] array.
>
> I noticed that issue while trying to optimize the parisc put_user() macro
> and used an intermediate variable to store the pointer. In that case I
> got this error:
>
> In file included from include/linux/uaccess.h:11,
> from include/linux/compat.h:17,
> from fs/fat/dir.c:18:
> fs/fat/dir.c: In function $B!F(Bfat_ioctl_filldir$B!G(B:
> fs/fat/dir.c:725:33: error: invalid initializer
> 725 | if (put_user(0, d2->d_name) || \
> | ^~
> include/asm/uaccess.h:152:33: note: in definition of macro $B!F(B__put_user$B!G(B
> 152 | __typeof__(ptr) __ptr = ptr; \
> | ^~~
> fs/fat/dir.c:759:1: note: in expansion of macro $B!F(BFAT_IOCTL_FILLDIR_FUNC$B!G(B
> 759 | FAT_IOCTL_FILLDIR_FUNC(fat_ioctl_filldir, __fat_dirent)
>
> The patch below cleans it up.
>
> Signed-off-by: Helge Deller <[email protected]>
Looks good.
Acked-by: OGAWA Hirofumi <[email protected]>
> diff --git a/fs/fat/dir.c b/fs/fat/dir.c
> index c4a274285858..249825017da7 100644
> --- a/fs/fat/dir.c
> +++ b/fs/fat/dir.c
> @@ -722,7 +722,7 @@ static int func(struct dir_context *ctx, const char *name, int name_len, \
> if (name_len >= sizeof(d1->d_name)) \
> name_len = sizeof(d1->d_name) - 1; \
> \
> - if (put_user(0, d2->d_name) || \
> + if (put_user(0, &d2->d_name[0]) || \
> put_user(0, &d2->d_reclen) || \
> copy_to_user(d1->d_name, name, name_len) || \
> put_user(0, d1->d_name + name_len) || \
--
OGAWA Hirofumi <[email protected]>
From: Helge Deller
> Sent: 14 February 2022 11:05
>
> On 2/14/22 10:26, David Laight wrote:
> > From: David Laight
> >> Sent: 14 February 2022 09:12
> >>
> >> From: Helge Deller
> >>> Sent: 13 February 2022 22:10
> >>>
> >>> The put_user(val,ptr) macro wants a pointer in the second parameter, but in
> >>> fat_ioctl_filldir() the d_name field references a whole "array of chars".
> >>> Usually the compiler automatically converts it and uses a pointer to that
> >>> array, but it's more clean to explicitly give the real pointer to where someting
> >>> is put, which is in this case the first character of the d_name[] array.
> >>
> >> That just isn't true.
> >>
> >> In C both x->char_array and &x->char_array[0] have the same type
> >> 'char *'.
> >>
> >> The 'bug' is caused by put_user() trying to do:
> >> __typeof__(ptr) __ptr = ptr;
> >> where __typeof__ is returning char[n] not char *.
> >>
> >> I've tried a few things but can't get __typeof__ to
> >> generate a suitable type for both a simple type and array.
> >
> > Actually the issue is that put_user() writes a single variable
> > and needs a pointer to one.
> > So changing to:
> > put_user(0, &array[0]);
> > is probably fine.
>
> Ok.
>
> > But the description is all wrong.
>
> I agree it can be improved.
> Would you mind proposing a better description?
put_user() needs a pointer to a simple type.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
On 2/14/22 10:27, Andreas Schwab wrote:
> On Feb 14 2022, David Laight wrote:
>
>> The 'bug' is caused by put_user() trying to do:
>> __typeof__(ptr) __ptr = ptr;
>> where __typeof__ is returning char[n] not char *.
>>
>> I've tried a few things but can't get __typeof__ to
>> generate a suitable type for both a simple type and array.
>
> Does it work to use __typeof__(&*(ptr))?
Yes, this works.
Helge