Commit f2d1362f authored Mar 22, 2016 by Nicolai Stange Committed by Herbert Xu Apr 05, 2016

lib/mpi: mpi_write_sgl(): fix skipping of leading zero limbs



Currently, if the number of leading zeros is greater than fits into a
complete limb, mpi_write_sgl() skips them by iterating over them limb-wise.

However, it fails to adjust its internal leading zeros tracking variable,
lzeros, accordingly: it does a

  p -= sizeof(alimb);
  continue;

which should really have been a

  lzeros -= sizeof(alimb);
  continue;

Since lzeros never decreases if its initial value >= sizeof(alimb), nothing
gets copied by mpi_write_sgl() in that case.

Instead of skipping the high order zero limbs within the loop as shown
above, fix the issue by adjusting the copying loop's bounds.

Fixes: 2d4d1eea ("lib/mpi: Add mpi sgl helpers")
Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

parent 3cf9d84e

lib/mpi/mpicoder.c

+9 −12

Original line number	Diff line number	Diff line
		@@ -380,7 +380,9 @@ int mpi_write_to_sgl(MPI a, struct scatterlist sgl, unsigned nbytes,
		buf_len = sgl->length;
		p2 = sg_virt(sgl);

		for (i = a->nlimbs - 1; i >= 0; i--) {
		for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
		lzeros %= BYTES_PER_MPI_LIMB;
		i >= 0; i--) {
		alimb = a->d[i];
		p = (u8 *)&alimb2;
		#if BYTES_PER_MPI_LIMB == 4
		@@ -401,17 +403,12 @@ int mpi_write_to_sgl(MPI a, struct scatterlist sgl, unsigned nbytes,
		#error please implement for this limb size.
		#endif
		if (lzeros > 0) {
		if (lzeros >= sizeof(alimb)) {
		p -= sizeof(alimb);
		continue;
		} else {
		mpi_limb_t limb1 = (void )p - sizeof(alimb);
		mpi_limb_t limb2 = (void )p - sizeof(alimb)
		+ lzeros;
		limb1 = limb2;
		p -= lzeros;
		y = lzeros;
		}
		lzeros -= sizeof(alimb);
		}

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