Messages in this thread | | | Date | Sat, 14 Apr 2012 00:53:40 +0200 (CEST) | From | Jesper Juhl <> | Subject | Re: [PATCH] mpi: Avoid using freed pointer in mpi_lshift_limbs() |
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On Thu, 12 Apr 2012, Kasatkin, Dmitry wrote:
> On Thu, Apr 12, 2012 at 1:31 AM, Jesper Juhl <jj@chaosbits.net> wrote: > > 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? > > > > > > Hello Jesper & James, > > That is of course correct. > > James, can you please apply this patch to security fixes? > > Acked-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com> >
Thank you for your time to review and your ACK :-)
-- Jesper Juhl <jj@chaosbits.net>
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