smb: avoid field overflow warning

  From: Arnd Bergmann <arnd@arndb.de>

clang warns about a possible field overflow in a memcpy:

In file included from fs/smb/server/smb_common.c:7:
include/linux/fortify-string.h:583:4: error: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
                        __write_overflow_field(p_size_field, size);

It appears to interpret the "&out[baselen + 4]" as referring to a single
byte of the character array, while the equivalen "out + baselen + 4" is
seen as an offset into the array.

I don't see that kind of warning elsewhere, so just go with the simple
rework.

Fixes: e2f34481b24db ("cifsd: add server-side procedures for SMB3")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 fs/smb/server/smb_common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
  

2023-06-16 18:07 GMT+09:00, Arnd Bergmann <arnd@kernel.org>:
> From: Arnd Bergmann <arnd@arndb.de>
Hi Arnd,

>
> clang warns about a possible field overflow in a memcpy:
>
> In file included from fs/smb/server/smb_common.c:7:
> include/linux/fortify-string.h:583:4: error: call to
> '__write_overflow_field' declared with 'warning' attribute: detected write
> beyond size of field (1st parameter); maybe use struct_group()?
> [-Werror,-Wattribute-warning]
>                         __write_overflow_field(p_size_field, size);
>
> It appears to interpret the "&out[baselen + 4]" as referring to a single
> byte of the character array, while the equivalen "out + baselen + 4" is
> seen as an offset into the array.
>
> I don't see that kind of warning elsewhere, so just go with the simple
> rework.
>
> Fixes: e2f34481b24db ("cifsd: add server-side procedures for SMB3")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  fs/smb/server/smb_common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/smb/server/smb_common.c b/fs/smb/server/smb_common.c
> index a7e81067bc991..e3273fa640b07 100644
> --- a/fs/smb/server/smb_common.c
> +++ b/fs/smb/server/smb_common.c
> @@ -536,7 +536,7 @@ int ksmbd_extract_shortname(struct ksmbd_conn *conn,
> const char *longname,
>  	out[baselen + 3] = PERIOD;
>
>  	if (dot_present)
> -		memcpy(&out[baselen + 4], extension, 4);
> +		memcpy(out + baselen + 4, extension, 1);
Is there any reason to change copy bytes from 4 bytes to 1 byte?

Thanks!
>  	else
>  		out[baselen + 4] = '\0';
>  	smbConvertToUTF16((__le16 *)shortname, out, PATH_MAX,
> --
> 2.39.2
>
>
  

On Fri, Jun 16, 2023, at 16:40, Namjae Jeon wrote:
> 2023-06-16 18:07 GMT+09:00, Arnd Bergmann <arnd@kernel.org>:
>> From: Arnd Bergmann <arnd@arndb.de>
>>
>> clang warns about a possible field overflow in a memcpy:
>>
>> In file included from fs/smb/server/smb_common.c:7:
>> include/linux/fortify-string.h:583:4: error: call to
>> '__write_overflow_field' declared with 'warning' attribute: detected write
>> beyond size of field (1st parameter); maybe use struct_group()?
>> [-Werror,-Wattribute-warning]
>>                         __write_overflow_field(p_size_field, size);
>>
>> It appears to interpret the "&out[baselen + 4]" as referring to a single
>> byte of the character array, while the equivalen "out + baselen + 4" is
>> seen as an offset into the array.
>>
>> I don't see that kind of warning elsewhere, so just go with the simple
>> rework.
>>
>> Fixes: e2f34481b24db ("cifsd: add server-side procedures for SMB3")
>> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>> ---
>>  fs/smb/server/smb_common.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/smb/server/smb_common.c b/fs/smb/server/smb_common.c
>> index a7e81067bc991..e3273fa640b07 100644
>> --- a/fs/smb/server/smb_common.c
>> +++ b/fs/smb/server/smb_common.c
>> @@ -536,7 +536,7 @@ int ksmbd_extract_shortname(struct ksmbd_conn *conn,
>> const char *longname,
>>  	out[baselen + 3] = PERIOD;
>>
>>  	if (dot_present)
>> -		memcpy(&out[baselen + 4], extension, 4);
>> +		memcpy(out + baselen + 4, extension, 1);
> Is there any reason to change copy bytes from 4 bytes to 1 byte?
>

No, that was an accident, this patch is wrong.

I have to revisit this one and check if my change actually still works
after I change it back to the correct length.

      Arnd
  

2023-06-16 23:42 GMT+09:00, Arnd Bergmann <arnd@arndb.de>:
> On Fri, Jun 16, 2023, at 16:40, Namjae Jeon wrote:
>> 2023-06-16 18:07 GMT+09:00, Arnd Bergmann <arnd@kernel.org>:
>>> From: Arnd Bergmann <arnd@arndb.de>
>>>
>>> clang warns about a possible field overflow in a memcpy:
>>>
>>> In file included from fs/smb/server/smb_common.c:7:
>>> include/linux/fortify-string.h:583:4: error: call to
>>> '__write_overflow_field' declared with 'warning' attribute: detected
>>> write
>>> beyond size of field (1st parameter); maybe use struct_group()?
>>> [-Werror,-Wattribute-warning]
>>>                         __write_overflow_field(p_size_field, size);
>>>
>>> It appears to interpret the "&out[baselen + 4]" as referring to a single
>>> byte of the character array, while the equivalen "out + baselen + 4" is
>>> seen as an offset into the array.
>>>
>>> I don't see that kind of warning elsewhere, so just go with the simple
>>> rework.
>>>
>>> Fixes: e2f34481b24db ("cifsd: add server-side procedures for SMB3")
>>> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>>> ---
>>>  fs/smb/server/smb_common.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/fs/smb/server/smb_common.c b/fs/smb/server/smb_common.c
>>> index a7e81067bc991..e3273fa640b07 100644
>>> --- a/fs/smb/server/smb_common.c
>>> +++ b/fs/smb/server/smb_common.c
>>> @@ -536,7 +536,7 @@ int ksmbd_extract_shortname(struct ksmbd_conn *conn,
>>> const char *longname,
>>>  	out[baselen + 3] = PERIOD;
>>>
>>>  	if (dot_present)
>>> -		memcpy(&out[baselen + 4], extension, 4);
>>> +		memcpy(out + baselen + 4, extension, 1);
>> Is there any reason to change copy bytes from 4 bytes to 1 byte?
>>
>
> No, that was an accident, this patch is wrong.
>
> I have to revisit this one and check if my change actually still works
> after I change it back to the correct length.
Okay:)
Thanks for your check!
>
>       Arnd
>