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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Nicolin Chen <nicoleotsuka@gmail.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Joerg Roedel <jroedel@suse.de>, Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.2 024/143] iommu/dma: Handle SG length overflow better
Date:   Wed,  4 Sep 2019 19:52:47 +0200
Message-Id: <20190904175315.013334397@linuxfoundation.org>
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[ Upstream commit ab2cbeb0ed301a9f0460078e91b09f39958212ef ]

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: 809eac54cdd6 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/iommu/dma-iommu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 379318266468c..8c02d2283d647 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -710,7 +710,7 @@ 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 {
-- 
2.20.1