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Re: [PATCH] linux: Clear mode_t padding bits (BZ#25623)
* Adhemerval Zanella:
> On 03/03/2020 18:51, Florian Weimer wrote:
>> * Adhemerval Zanella:
>>
>>> diff --git a/sysdeps/unix/sysv/linux/msgctl.c b/sysdeps/unix/sysv/linux/msgctl.c
>>> index 27879e76cd..48801a3fba 100644
>>> --- a/sysdeps/unix/sysv/linux/msgctl.c
>>> +++ b/sysdeps/unix/sysv/linux/msgctl.c
>>
>>> +#else
>>> + /* Old Linux kernel versions might not clear the mode padding. */
>>> + if (sizeof ((struct msqid_ds){0}.msg_perm.mode
>>> + != sizeof ((struct __old_ipc_perm){0}.mode)))
>>> + buf->msg_perm.mode &= 0xFFFF;
>>> +#endif
>>
>> The condition always evaluates to true becaduse the first sizeof is
>> applied to the result of the != operator.
>
> Sigh, indeed (I should have verified if x86_64 resulting code would be
> constant). Is is ok with the suppose fix (below)?
>
> if (sizeof ((struct msqid_ds){0}.msg_perm.mode)
> != sizeof ((struct __old_ipc_perm){0}.mode))
> buf->msg_perm.mode &= 0xFFFF;
That looks better. Is there case where the sizes are the same and 32
bits?
Thanks,
Florian