lib/scatterlist: Avoid potential scatterlist entry overflow
Since the scatterlist length field is an unsigned int, make
sure that sg_alloc_table_from_pages does not overflow it while
coalescing pages to a single entry.
v2: Drop reference to future use. Use UINT_MAX.
v3: max_segment must be page aligned.
v4: Do not rely on compiler to optimise out the rounddown.
(Joonas Lahtinen)
v5: Simplified loops and use post-increments rather than
pre-increments. Use PAGE_MASK and fix comment typo.
(Andy Shevchenko)
v6: Commit spelling fix.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170803091312.22875-1-tvrtko.ursulin@linux.intel.com
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index dee0c50..7b2e74d 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -394,17 +394,22 @@ int sg_alloc_table_from_pages(struct sg_table *sgt,
unsigned int offset, unsigned long size,
gfp_t gfp_mask)
{
- unsigned int chunks;
- unsigned int i;
- unsigned int cur_page;
+ const unsigned int max_segment = SCATTERLIST_MAX_SEGMENT;
+ unsigned int chunks, cur_page, seg_len, i;
int ret;
struct scatterlist *s;
/* 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)
- ++chunks;
+ seg_len = 0;
+ for (i = 1; i < n_pages; i++) {
+ seg_len += PAGE_SIZE;
+ if (seg_len >= max_segment ||
+ page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1) {
+ chunks++;
+ seg_len = 0;
+ }
+ }
ret = sg_alloc_table(sgt, chunks, gfp_mask);
if (unlikely(ret))
@@ -413,17 +418,21 @@ 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 j;
+ unsigned int j, chunk_size;
/* look for the end of the current chunk */
- for (j = cur_page + 1; j < n_pages; ++j)
- if (page_to_pfn(pages[j]) !=
+ seg_len = 0;
+ for (j = cur_page + 1; j < n_pages; j++) {
+ seg_len += PAGE_SIZE;
+ if (seg_len >= max_segment ||
+ page_to_pfn(pages[j]) !=
page_to_pfn(pages[j - 1]) + 1)
break;
+ }
chunk_size = ((j - cur_page) << PAGE_SHIFT) - 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;