linux-kernel - [PATCH v2] iommu/dma: Fix check for error return from iommu_map_sg

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Message-Id: <20220517102912.2115228-1-schnelle@linux.ibm.com>
Date:   Tue, 17 May 2022 12:29:12 +0200
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>
Cc:     Christoph Hellwig <hch@....de>, Jason Gunthorpe <jgg@...dia.com>,
        Robin Murphy <robin.murphy@....com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org
Subject: [PATCH v2] iommu/dma: Fix check for error return from iommu_map_sg_atomic()

In __iommu_dma_alloc_noncontiguous() the return value of
iommu_map_sg_atomic() is treated as an error if it is smaller than size.
Before upstream commit ad8f36e4b6b1 ("iommu: return full error code from
iommu_map_sg[_atomic]()") this simply checked if the requested size was
successfully mapped.

After that commit iommu_map_sg_atomic() may also return a negative
error value. In principle this too would be covered by the existing
check. There is one problem however, as size is of type size_t while the
return type of iommu_map_sg_atomic() is now of type ssize_t the latter gets
converted to size_t and negative error values end up as very large
positive values making the check succeed even if an error was returned.
Fix this by casting size to ssize_t.

Fixes: ad8f36e4b6b1 ("iommu: return full error code from iommu_map_sg[_atomic]()")
Cc: stable@...r.kernel.org
Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
---
v1 -> v2:
- Don't needlessly add a local variable

 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 09f6e1c0f9c0..80db2aa5458c 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -814,7 +814,7 @@ static struct page **__iommu_dma_alloc_noncontiguous(struct device *dev,
 	}

 	if (iommu_map_sg_atomic(domain, iova, sgt->sgl, sgt->orig_nents, ioprot)
-			< size)
+			< (ssize_t)size)
 		goto out_free_sg;

 	sgt->sgl->dma_address = iova;
-- 
2.32.0