Le 29/05/2018 à 11:05, Geert Uytterhoeven a écrit :
> Hi Christophe,
>
> On Tue, May 29, 2018 at 10:56 AM, Christophe LEROY
> <christophe.leroy at c-s.fr> wrote:
>> Le 29/05/2018 à 09:47, Geert Uytterhoeven a écrit :
>>> On Tue, May 29, 2018 at 8:03 AM, Christophe Leroy
>>> <christophe.leroy at c-s.fr> wrote:
>>>>
>>>> CC arch/powerpc/kernel/nvram_64.o
>>>> arch/powerpc/kernel/nvram_64.c: In function 'nvram_create_partition':
>>>> arch/powerpc/kernel/nvram_64.c:1042:2: error: 'strncpy' specified bound
>>>> 12 equals destination size [-Werror=stringop-truncation]
>>>> strncpy(new_part->header.name, name, 12);
>>>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>
>>>> CC arch/powerpc/kernel/trace/ftrace.o
>>>> In function 'make_field',
>>>> inlined from 'ps3_repository_read_boot_dat_address' at
>>>> arch/powerpc/platforms/ps3/repository.c:900:9:
>>>> arch/powerpc/platforms/ps3/repository.c:106:2: error: 'strncpy' output
>>>> truncated before terminating nul copying 8 bytes from a string of the same
>>>> length [-Werror=stringop-truncation]
>>>> strncpy((char *)&n, text, 8);
>>>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>
>>>> Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
>>>
>>>
>>> Thanks for your patch!
>>>
>>>> --- a/arch/powerpc/kernel/nvram_64.c
>>>> +++ b/arch/powerpc/kernel/nvram_64.c
>>>> @@ -1039,7 +1039,7 @@ loff_t __init nvram_create_partition(const char
>>>> *name, int sig,
>>>> new_part->index = free_part->index;
>>>> new_part->header.signature = sig;
>>>> new_part->header.length = size;
>>>> - strncpy(new_part->header.name, name, 12);
>>>> + memcpy(new_part->header.name, name, strnlen(name,
>>>> sizeof(new_part->header.name)));
>>>
>>>
>>> The comment for nvram_header.lgnth says:
>>>
>>> /* Terminating null required only for names < 12 chars. */
>>>
>>> This will not terminate the string with a zero (the struct is
>>> allocated with kmalloc).
>>> So the original code is correct, the new one isn't.
>>
>> Right, then I have to first zeroize the destination.
>
> Using kzalloc() instead of kmalloc() will do.
>
> Still, papering around these warnings seems to obscure things, IMHO.
> And it increases code size, as you had to add a call to strnlen().
Right but then, what is the best solution to elimate that warning ?
Would it be better to enclose those two lines in:
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wstringop-truncation"
...
#pragma GCC diagnostic pop
Christophe
>
>>>> new_part->header.checksum = nvram_checksum(&new_part->header);
>>>>
>>>> rc = nvram_write_header(new_part);
>>>> diff --git a/arch/powerpc/platforms/ps3/repository.c
>>>> b/arch/powerpc/platforms/ps3/repository.c
>>>> index 50dbaf24b1ee..e49c887787c4 100644
>>>> --- a/arch/powerpc/platforms/ps3/repository.c
>>>> +++ b/arch/powerpc/platforms/ps3/repository.c
>>>> @@ -101,9 +101,9 @@ static u64 make_first_field(const char *text, u64
>>>> index)
>>>>
>>>> static u64 make_field(const char *text, u64 index)
>>>> {
>>>> - u64 n;
>>>> + u64 n = 0;
>>>>
>>>> - strncpy((char *)&n, text, 8);
>>>> + memcpy((char *)&n, text, strnlen(text, sizeof(n)));
>>>
>>>
>>> This changes behavior: strncpy() fills the remainder of the buffer with
>>> zeroes. I don't remember the details of the PS3 repository structure,
>>> but given this writes to a fixed size u64 buffer, I'd expect the PS3
>>> hypervisor code to (1) rely on the zero padding, and (2) not need a zero
>>> terminator if there are 8 characters in the buffer, so probably the
>>> original code is correct, and the "fixed" code isn't.
>>
>> Here I have set n to 0 prior to the copy, so the buffer IS zero padded.
>
> Sorry, I missed that part.
>
> Gr{oetje,eeting}s,
>
> Geert
>