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iommu/dma: Handle SG length overflow better

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Since scatterlist dimensions are all unsigned ints, in the relatively
rare cases where a device's max_segment_size is set to UINT_MAX, then
the "cur_len + s_length <= max_len" check in __finalise_sg() will always
return true. As a result, the corner case of such a device mapping an
excessively large scatterlist which is mergeable to or beyond a total
length of 4GB can lead to overflow and a bogus truncated dma_length in
the resulting segment.

As we already assume that any single segment must be no longer than
max_len to begin with, this can easily be addressed by reshuffling the
comparison.

Fixes: 809eac54cd ("iommu/dma: Implement scatterlist segment merging")
Reported-by: Nicolin Chen <nicoleotsuka@gmail.com>
Tested-by: Nicolin Chen <nicoleotsuka@gmail.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
This commit is contained in:
Robin Murphy 2019-07-29 17:46:00 +01:00 committed by Joerg Roedel
parent bfeaec7f7d
commit ab2cbeb0ed
1 changed files with 1 additions and 1 deletions
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2
drivers/iommu/dma-iommu.c
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@ -762,7 +762,7 @@ static int __finalise_sg(struct device *dev, struct scatterlist *sg, int nents,
* - and wouldn't make the resulting output segment too long
*/
if (cur_len && !s_iova_off && (dma_addr & seg_mask) &&
(cur_len + s_length <= max_len)) {
(max_len - cur_len >= s_length)) {
/* ...then concatenate it with the previous one */
cur_len += s_length;
} else {