> On Feb 15, 2016, at 11:01, Deepa Dinamani <deepa.kernel@xxxxxxxxx> wrote:
>
> long/ kernel_time_t is 32 bit on a 32 bit system and
> 64 bit on a 64 bit system.
>
> ceph_encode_timespec() encodes only the lower 32 bits on
> a 64 bit system and encodes all of 32 bits on a 32bit
> system.
>
> ceph_decode_timespec() decodes 32 bit tv_sec and tv_nsec
> into kernel_time_t/ long.
>
> The encode and decode functions do not match when the
> values are negative:
>
> Consider the following scenario on a 32 bit system:
> When a negative number is cast to u32 as encode does, the
> value is positive and is greater than INT_MAX. Decode reads
> back this value. And, this value cannot be represented by
> long on 32 bit systems. So by section 6.3.1.3 of the
> C99 standard, the result is implementation defined.
>
> Consider the following scenario on a 64 bit system:
> When a negative number is cast to u32 as encode does, the
> value is positive. This value is later assigned by decode
> function by a cast to long. Since this value can be
> represented in long data type, this becomes a positive
> value greater than INT_MAX. But, the value encoded was
> negative, so the encode and decode functions do not match.
>
> Change the decode function as follows to overcome the above
> bug:
> The decode should first cast the value to a s64 this will
> be positive value greater than INT_MAX(in case of a negative
> encoded value)and then cast this value again as s32, which
> drops the higher order 32 bits.
> On 32 bit systems, this is the right value in kernel_time_t/
> long.
> On 64 bit systems, assignment to kernel_time_t/ long
> will sign extend this value to reflect the signed bit encoded.
>
> Assume ceph timestamp ranges permitted are 1902..2038.
>
> Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
> Signed-off-by: Deepa Dinamani <deepa.kernel@xxxxxxxxx>
> ---
> include/linux/ceph/decode.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/ceph/decode.h b/include/linux/ceph/decode.h
> index a6ef9cc..e777e99 100644
> --- a/include/linux/ceph/decode.h
> +++ b/include/linux/ceph/decode.h
> @@ -137,8 +137,8 @@ bad:
> static inline void ceph_decode_timespec(struct timespec *ts,
> const struct ceph_timespec *tv)
> {
> - ts->tv_sec = (__kernel_time_t)le32_to_cpu(tv->tv_sec);
> - ts->tv_nsec = (long)le32_to_cpu(tv->tv_nsec);
> + ts->tv_sec = (s32)(s64)le32_to_cpu(tv->tv_sec);
> + ts->tv_nsec = (s32)(s64)le32_to_cpu(tv->tv_nsec);
> }
> static inline void ceph_encode_timespec(struct ceph_timespec *tv,
> const struct timespec *ts)
Applied, thanks
Yan, Zheng
> --
> 1.9.1
>
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