On Fri, Nov 11, 2016 at 08:50:18AM +0000, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>
> Since the scatterlist length field is an unsigned int, make
> sure that sg_alloc_table_from_pages does not overflow it while
> coallescing pages to a single entry.
>
> v2: Drop reference to future use. Use UINT_MAX.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
> lib/scatterlist.c | 25 +++++++++++++++++++------
> 1 file changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/lib/scatterlist.c b/lib/scatterlist.c
> index e05e7fc98892..de15f369b317 100644
> --- a/lib/scatterlist.c
> +++ b/lib/scatterlist.c
> @@ -394,7 +394,8 @@ int sg_alloc_table_from_pages(struct sg_table *sgt,
> unsigned int offset, unsigned long size,
> gfp_t gfp_mask)
> {
> - unsigned int chunks;
> + const unsigned int max_segment = UINT_MAX;
> + unsigned int seg_len, chunks;
> unsigned int i;
> unsigned int cur_page;
> int ret;
> @@ -402,9 +403,16 @@ int sg_alloc_table_from_pages(struct sg_table *sgt,
>
> /* compute number of contiguous chunks */
> chunks = 1;
> - for (i = 1; i < n_pages; ++i)
> - if (page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1)
> + seg_len = PAGE_SIZE;
> + for (i = 1; i < n_pages; ++i) {
> + if (seg_len >= max_segment ||
> + page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1) {
> ++chunks;
> + seg_len = PAGE_SIZE;
> + } else {
> + seg_len += PAGE_SIZE;
> + }
> + }
>
> ret = sg_alloc_table(sgt, chunks, gfp_mask);
> if (unlikely(ret))
> @@ -413,17 +421,22 @@ int sg_alloc_table_from_pages(struct sg_table *sgt,
> /* merging chunks and putting them into the scatterlist */
> cur_page = 0;
> for_each_sg(sgt->sgl, s, sgt->orig_nents, i) {
> - unsigned long chunk_size;
> + unsigned int chunk_size;
> unsigned int j;
>
> /* look for the end of the current chunk */
> + seg_len = PAGE_SIZE;
> for (j = cur_page + 1; j < n_pages; ++j)
> - if (page_to_pfn(pages[j]) !=
> + if (seg_len >= max_segment ||
> + page_to_pfn(pages[j]) !=
> page_to_pfn(pages[j - 1]) + 1)
> break;
> + else
> + seg_len += PAGE_SIZE;
>
> chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset;
chunk_size = seg_len - offset;
?
> - sg_set_page(s, pages[cur_page], min(size, chunk_size), offset);
> + sg_set_page(s, pages[cur_page],
> + min_t(unsigned long, size, chunk_size), offset);
> size -= chunk_size;
> offset = 0;
> cur_page = j;
Could BUG_ON(size); afterwards and BUG_ON(!size) inside? Although that
requires the caller didn't make a mistake in n_pages vs offset+size.
Minor comments,
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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