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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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