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Subject[PATCH 2/4] lib/scatterlist: Avoid potential scatterlist entry overflow
Date
From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

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.
v3: max_segment must be page aligned.

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> (v2)
---
lib/scatterlist.c | 25 +++++++++++++++++++------
1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index e05e7fc98892..4fc54801cd29 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 = rounddown(UINT_MAX, PAGE_SIZE);
+ 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;
- 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;
--
2.7.4
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