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lib/scatterlist: Avoid potential scatterlist entry overflow

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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
This commit is contained in:
Tvrtko Ursulin 2017-08-03 10:13:12 +01:00
parent c4860ad605
commit c125906b83
2 changed files with 26 additions and 11 deletions
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6
include/linux/scatterlist.h
View File

@ -20,6 +20,12 @@ struct scatterlist {
#endif
};
/*
* Since the above length field is an unsigned int, below we define the maximum
* length in bytes that can be stored in one scatterlist entry.
*/
#define SCATTERLIST_MAX_SEGMENT (UINT_MAX & PAGE_MASK)
/*
* These macros should be used after a dma_map_sg call has been done
* to get bus addresses of each of the SG entries and their lengths.

31
lib/scatterlist.c
View File

@ -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;