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Date: Thu, 17 Mar 2016 18:59:59 +0100 From: Nicolai Stange <nicstange@...il.com> To: Herbert Xu <herbert@...dor.apana.org.au> Cc: Tadeusz Struk <tadeusz.struk@...el.com>, Michal Marek <mmarek@...e.com>, Andrzej Zaborowski <andrew.zaborowski@...el.com>, Stephan Mueller <smueller@...onox.de>, Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org, Nicolai Stange <nicstange@...il.com> Subject: [PATCH 1/8] 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: 2d4d1eea540b ("lib/mpi: Add mpi sgl helpers") Signed-off-by: Nicolai Stange <nicstange@...il.com> --- lib/mpi/mpicoder.c | 21 +++++++++------------ 1 file changed, 9 insertions(+), 12 deletions(-) diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c index eb15e7d..6bb52be 100644 --- a/lib/mpi/mpicoder.c +++ b/lib/mpi/mpicoder.c @@ -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; - } + 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); } -- 2.7.2
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