Re: [PATCH] Block: Fix block/elevator.c elevator_get() off-by-one error

[Xiaotian Feng]

On Tue, Mar 30, 2010 at 5:21 PM,  <wzt.wzt@xxxxxxxxx> wrote:
> elevator_get() not check the name length, if the name length > sizeof(elv),
> elv will miss the '\0'. And elv buffer will be replace "-iosched" as something
> like aaaaaaaaa, then call request_module() can load an not trust module.
>
> Signed-off-by: Zhitong Wang <zhitong.wangzt@xxxxxxxxxxxxxxx>
>
> ---
> Âblock/elevator.c | Â Â2 +-
> Â1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/block/elevator.c b/block/elevator.c
> index df75676..76e3702 100644
> --- a/block/elevator.c
> +++ b/block/elevator.c
> @@ -154,7 +154,7 @@ static struct elevator_type *elevator_get(const char *name)
>
> Â Â Â Â Â Â Â Âspin_unlock(&elv_list_lock);
>
> - Â Â Â Â Â Â Â sprintf(elv, "%s-iosched", name);
> + Â Â Â Â Â Â Â snprintf(elv, sizeof(elv), "%s-iosched", name);
>

elv is defined as char elv[ELV_NAME_MAX + strlen("-iosched")];
so if name length > sizeof(elv), the name length must already bigger
than ELV_NAME_MAX

elevator_get is used in elevator_init, so if elevator_init is passing
a super long name, why not just return -EINVAL?
In this patch, if we pass a super long name, we're still trying to cut
it and request_module an invalid name, right?
Although '\0' is kept, but name is still invalid, right?


> Â Â Â Â Â Â Â Ârequest_module("%s", elv);
> Â Â Â Â Â Â Â Âspin_lock(&elv_list_lock);
> --
> 1.6.5.3
>
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