On Wed, Feb 16, 2011 at 5:49 PM, Li Zefan <lizf@xxxxxxxxxxxxxx> wrote:
> It's not necessary to copy cpuset->mems_allowed to a buffer
> allocated by NODEMASK_ALLOC(). Just pass it to nodelist_scnprintf().
>
> Signed-off-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
Acked-by: Paul Menage <menage@xxxxxxxxxx>
The only downside is that we're now doing more work (and more complex
work) inside callback_mutex, but I guess that's OK compared to having
to do a memory allocation. (I poked around in lib/vsprintf.c and I
couldn't see any cases where it might allocate memory, but it would be
particularly bad if there was any way to trigger an Oops.)
> ---
> kernel/cpuset.c | 10 +---------
> 1 files changed, 1 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index 10f1835..f13ff2e 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -1620,20 +1620,12 @@ static int cpuset_sprintf_cpulist(char *page, struct cpuset *cs)
>
> static int cpuset_sprintf_memlist(char *page, struct cpuset *cs)
> {
> - NODEMASK_ALLOC(nodemask_t, mask, GFP_KERNEL);
> int retval;
>
> - if (mask == NULL)
> - return -ENOMEM;
> -
And this was particularly broken since the only caller of
cpuset_sprintf_memlist() doesn't handle a negative error response
anyway and would then overwrite byte 4083 on the preceding page with a
'\n'. And then since the (size_t)(s-page) that's passed to
simple_read_from_buffer() would be a very large number, it would write
arbitrary (user-controlled) amounts of kernel data to the userspace
buffer.
Maybe we could also rename 'retval' to 'count' in this function (and
cpuset_sprintf_cpulist()) to make it clearer that callers don't expect
negative error values?
> mutex_lock(&callback_mutex);
> - *mask = cs->mems_allowed;
> + retval = nodelist_scnprintf(page, PAGE_SIZE, cs->mems_allowed);
> mutex_unlock(&callback_mutex);
>
> - retval = nodelist_scnprintf(page, PAGE_SIZE, *mask);
> -
> - NODEMASK_FREE(mask);
> -
> return retval;
> }
>
> --
> 1.7.3.1
>
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