On Sun 05-05-13 23:43:10, Sha Zhengju wrote:
> Since PAGE_ALIGN is aligning up(the next page boundary), this can
> prevent input values wrapped to 0 and cause strange result to user.
I guess you wanted to say that it can cause an overflow, right?
"
Since PAGE_ALIGN is aligning up (to the next page boundary), this can
cause an overflow to 0 if >= ULLONG_MAX-4094 value is given in the
buffer.
"
>
> This patch also rename the second arg of
> res_counter_memparse_write_strategy() to 'resp' and add a local
> variable 'res' to save the too often dereferences. Thanks Andrew
> for pointing it out!
Again, it would be nicer to have this cleanup in a separate patch.
> Signed-off-by: Sha Zhengju <handai.szj@xxxxxxxxxx>
> Reported-by: Li Wenpeng <xingke.lwp@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
We have this bug since ever and nobody has noticed so nobody seems to
use
> ---
> kernel/res_counter.c | 18 ++++++++++++------
> 1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/res_counter.c b/kernel/res_counter.c
> index 3f0417f..be8ddda 100644
> --- a/kernel/res_counter.c
> +++ b/kernel/res_counter.c
> @@ -178,23 +178,29 @@ u64 res_counter_read_u64(struct res_counter *counter, int member)
> #endif
>
> int res_counter_memparse_write_strategy(const char *buf,
> - unsigned long long *res)
> + unsigned long long *resp)
> {
> char *end;
> + unsigned long long res;
>
> /* return RES_COUNTER_MAX(unlimited) if "-1" is specified */
> if (*buf == '-') {
> - *res = simple_strtoull(buf + 1, &end, 10);
> - if (*res != 1 || *end != '\0')
> + res = simple_strtoull(buf + 1, &end, 10);
> + if (res != 1 || *end != '\0')
> return -EINVAL;
> - *res = RES_COUNTER_MAX;
> + *resp = RES_COUNTER_MAX;
> return 0;
> }
>
> - *res = memparse(buf, &end);
> + res = memparse(buf, &end);
> if (*end != '\0')
> return -EINVAL;
>
> - *res = PAGE_ALIGN(*res);
> + if (PAGE_ALIGN(res) >= res)
> + res = PAGE_ALIGN(res);
> + else
> + res = RES_COUNTER_MAX; /* avoid PAGE_ALIGN wrapping to zero */
> +
> + *resp = res;
> return 0;
> }
> --
> 1.7.9.5
>
--
Michal Hocko
SUSE Labs
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