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    SubjectRe: [PATCH] mpi: Avoid using freed pointer in mpi_lshift_limbs()
    On Tue, 13 Mar 2012, Kasatkin, Dmitry wrote:

    > On Thu, Mar 1, 2012 at 11:33 PM, Jesper Juhl <jj@chaosbits.net> wrote:
    > >
    > > Ping?
    > >
    > > On Mon, 6 Feb 2012, Jesper Juhl wrote:
    > >
    > >> At the start of the function we assign 'a->d' to 'ap'. Then we use the
    > >> RESIZE_IF_NEEDED macro on 'a' - this may free 'a->d' and replace it
    > >> with newly allocaetd storage. In that case, we'll be operating on
    > >> freed memory further down in the function when we index into 'ap[]'.
    > >> Since we don't actually need 'ap' until after the use of the
    > >> RESIZE_IF_NEEDED macro we can just delay the assignment to it until
    > >> after we've potentially resized, thus avoiding the issue.
    > >>
    > >> While I was there anyway I also changed the integer variable 'n' to be
    > >> const. It might as well be since we only assign to it once and use it
    > >> as a constant, and then the compiler will tell us if we ever assign to
    > >> it in the future.
    > >>
    > >> Signed-off-by: Jesper Juhl <jj@chaosbits.net>
    > >> ---
    > >>  lib/mpi/mpi-bit.c |    5 +++--
    > >>  1 files changed, 3 insertions(+), 2 deletions(-)
    > >>
    > >>  only compile tested.
    > >>
    > >> diff --git a/lib/mpi/mpi-bit.c b/lib/mpi/mpi-bit.c
    > >> index 2f52662..0c50536 100644
    > >> --- a/lib/mpi/mpi-bit.c
    > >> +++ b/lib/mpi/mpi-bit.c
    > >> @@ -177,8 +177,8 @@ int mpi_rshift(MPI x, MPI a, unsigned n)
    > >>   */
    > >>  int mpi_lshift_limbs(MPI a, unsigned int count)
    > >>  {
    > >> -     mpi_ptr_t ap = a->d;
    > >> -     int n = a->nlimbs;
    > >> +     const int n = a->nlimbs;
    > >> +     mpi_ptr_t ap;
    > >>       int i;
    > >>
    > >>       if (!count || !n)
    > >> @@ -187,6 +187,7 @@ int mpi_lshift_limbs(MPI a, unsigned int count)
    > >>       if (RESIZE_IF_NEEDED(a, n + count) < 0)
    > >>               return -ENOMEM;
    > >>
    > >> +     ap = a->d;
    > >>       for (i = n - 1; i >= 0; i--)
    > >>               ap[i + count] = ap[i];
    > >>       for (i = 0; i < count; i++)
    > >>
    > >
    > > --
    > > Jesper Juhl <jj@chaosbits.net>       http://www.chaosbits.net/
    > > Don't top-post http://www.catb.org/jargon/html/T/top-post.html
    > > Plain text mails only, please.
    > >
    > > --
    > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    > > the body of a message to majordomo@vger.kernel.org
    > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
    > > Please read the FAQ at  http://www.tux.org/lkml/
    >
    > Hello,
    >
    > I was travelling last week.
    > I will review the patch now..
    >

    Hi.

    Did you get a chance to review the patch? Did you find it acceptable or
    flawed?

    If it is OK, what do I need to from this point forward to get it merged?


    --
    Jesper Juhl <jj@chaosbits.net> http://www.chaosbits.net/
    Don't top-post http://www.catb.org/jargon/html/T/top-post.html
    Plain text mails only, please.
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