FAILED: patch "[PATCH] iommu/dma: Catch scatterlist length overflows" failed to apply to 5.15-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 1c8f6308e557f32412e9d4678b3f029f47f6d9aa
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107060343-failed-5.15-1c8f6308e557@kernel.org' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 1c8f6308e557f32412e9d4678b3f029f47f6d9aa Mon Sep 17 00:00:00 2001
From: Krzysztof Karas <krzysztof.karas@intel.com>
Date: Fri, 2 Oct 2026 05:33:20 +0000
Subject: [PATCH] iommu/dma: Catch scatterlist length overflows

It is possible, when a very large mapping uses only one
scatterlist, that padding overflows scatterlist's length field.
This results in:
 1) silently wrapping the value
 2) smaller than desired mappings produced by iommu_map_sg
 3) leaving mapped bytes in memory (no iommu_unmap)

Address this issue by adding overflow detection for scatterlist
length field.

Fixes: 809eac54cdd6 ("iommu/dma: Implement scatterlist segment merging")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Krzysztof Karas <krzysztof.karas@intel.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Sebastian Brzezinka <sebastian.brzezinka@intel.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
---
 drivers/iommu/dma-iommu.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 1b80121232322..c19f668a7be9b 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -1478,6 +1478,11 @@ int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
 		sg_dma_len(s) = s_length;
 		s->offset -= s_iova_off;
 		s_length = iova_align(iovad, s_length + s_iova_off);
+		if (overflows_type(s_length, s->length)) {
+			ret = -EOVERFLOW;
+
+			goto out_restore_sg;
+		}
 		s->length = s_length;
 
 		/*
@@ -1494,7 +1499,20 @@ int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
 		 *   time through here (i.e. before it has a meaningful value).
 		 */
 		if (pad_len && pad_len < s_length - 1) {
-			prev->length += pad_len;
+			unsigned int new_prev_len;
+
+			/*
+			 * For large mappings spanning multiple GBs we
+			 * may not be able to fit all needed padding into
+			 * sg->length.
+			 */
+			if (check_add_overflow(prev->length, pad_len, &new_prev_len)) {
+				ret = -EOVERFLOW;
+
+				goto out_restore_sg;
+			}
+
+			prev->length = new_prev_len;
 			iova_len += pad_len;
 		}
 
-- 
2.53.0