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    SubjectRe: [PATCH] Block: Fix block/elevator.c elevator_get() off-by-one error
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    On Tue, Mar 30, 2010 at 5:21 PM,  <wzt.wzt@gmail.com> 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@alibaba-inc.com>
    >
    > ---
    >  block/elevator.c |    2 +-
    >  1 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)
    >
    >                spin_unlock(&elv_list_lock);
    >
    > -               sprintf(elv, "%s-iosched", name);
    > +               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?


    >                request_module("%s", elv);
    >                spin_lock(&elv_list_lock);
    > --
    > 1.6.5.3
    >
    > --
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