Re: [PATCH] mpi: Avoid using freed pointer in mpi_lshift_limbs()

[Kasatkin, Dmitry]

On Thu, Apr 12, 2012 at 1:31 AM, Jesper Juhl <jj@xxxxxxxxxxxxx> wrote:
> On Tue, 13 Mar 2012, Kasatkin, Dmitry wrote:
>
>> On Thu, Mar 1, 2012 at 11:33 PM, Jesper Juhl <jj@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
>> >> ---
>> >> Âlib/mpi/mpi-bit.c | Â Â5 +++--
>> >> Â1 files changed, 3 insertions(+), 2 deletions(-)
>> >>
>> >> Âonly 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)
>> >> Â */
>> >> Âint mpi_lshift_limbs(MPI a, unsigned int count)
>> >> Â{
>> >> - Â Â mpi_ptr_t ap = a->d;
>> >> - Â Â int n = a->nlimbs;
>> >> + Â Â const int n = a->nlimbs;
>> >> + Â Â mpi_ptr_t ap;
>> >> Â Â Â int i;
>> >>
>> >> Â Â Â if (!count || !n)
>> >> @@ -187,6 +187,7 @@ int mpi_lshift_limbs(MPI a, unsigned int count)
>> >> Â Â Â if (RESIZE_IF_NEEDED(a, n + count) < 0)
>> >> Â Â Â Â Â Â Â return -ENOMEM;
>> >>
>> >> + Â Â ap = a->d;
>> >> Â Â Â for (i = n - 1; i >= 0; i--)
>> >> Â Â Â Â Â Â Â ap[i + count] = ap[i];
>> >> Â Â Â for (i = 0; i < count; i++)
>> >>
>> >
>> > --
>> > Jesper Juhl <jj@xxxxxxxxxxxxx> Â Â Â 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
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>>
>> Hello,
>>
>> I was travelling last week.
>> I will review the patch now..
>>
>
> Hi.
>
> Did you get a chance to review the patch? ÂDid you find it acceptable or
> flawed?
>
> If it is OK, what do I need to from this point forward to get it merged?
>
>

Hello Jesper & James,

That is of course correct.

James, can you please apply this patch to security fixes?

 Acked-by: Dmitry Kasatkin <dmitry.kasatkin@xxxxxxxxx>

- Dmitry

> --
> Jesper Juhl <jj@xxxxxxxxxxxxx> Â Â Â 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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