Messages in this thread | | | Date | Tue, 13 Mar 2012 14:34:32 +0200 | Subject | Re: [PATCH] mpi: Avoid using freed pointer in mpi_lshift_limbs() | From | "Kasatkin, Dmitry" <> |
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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..
Thanks, Dmitry -- 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/
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