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SubjectRe: [PATCH v2] fs: select: fix information leak to userspace
On Sun, 14 Nov 2010 12:25:33 +0300 Vasiliy Kulikov <segoon@openwall.com> wrote:

> On some architectures __kernel_suseconds_t is int. On these archs
> struct timeval has padding bytes at the end. This struct is copied to
> userspace with these padding bytes uninitialized. This leads to leaking
> of contents of kernel stack memory.
>
> Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
> ---
> Patch v1 used memset(), it was waste of cycles on almost all archs.
>
> Compile tested.
>
> fs/select.c | 7 ++++---
> 1 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/fs/select.c b/fs/select.c
> index b7b10aa..43d4805 100644
> --- a/fs/select.c
> +++ b/fs/select.c
> @@ -288,7 +288,6 @@ static int poll_select_copy_remaining(struct timespec *end_time, void __user *p,
> int timeval, int ret)
> {
> struct timespec rts;
> - struct timeval rtv;
>
> if (!p)
> return ret;
> @@ -306,8 +305,10 @@ static int poll_select_copy_remaining(struct timespec *end_time, void __user *p,
> rts.tv_sec = rts.tv_nsec = 0;
>
> if (timeval) {
> - rtv.tv_sec = rts.tv_sec;
> - rtv.tv_usec = rts.tv_nsec / NSEC_PER_USEC;
> + struct timeval rtv = {
> + .tv_sec = rts.tv_sec,
> + .tv_usec = rts.tv_nsec / NSEC_PER_USEC
> + };
>
> if (!copy_to_user(p, &rtv, sizeof(rtv)))
> return ret;

Please check the assembly code - this will still leave four bytes of
uninitalised stack data in 'rtv', surely.



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