[PATCH][next] iommu/virtio: Add __counted_by for struct viommu_request and use struct_size()

Gustavo A. R. Silva
2023-10-09T18:24:36Z

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

While there, use struct_size() helper, instead of the open-coded
version, to calculate the size for the allocation of the whole
flexible structure, including of course, the flexible-array member.

This code was found with the help of Coccinelle, and audited and
fixed manually.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
drivers/iommu/virtio-iommu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
index 17dcd826f5c2..379ebe03efb6 100644
--- a/drivers/iommu/virtio-iommu.c
+++ b/drivers/iommu/virtio-iommu.c
@@ -85,7 +85,7 @@ struct viommu_request {
void *writeback;
unsigned int write_offset;
unsigned int len;
- char buf[];
+ char buf[] __counted_by(len);
};

#define VIOMMU_FAULT_RESV_MASK 0xffffff00
@@ -230,7 +230,7 @@ static int __viommu_add_req(struct viommu_dev *viommu, void *buf, size_t len,
if (write_offset <= 0)
return -EINVAL;

- req = kzalloc(sizeof(*req) + len, GFP_ATOMIC);
+ req = kzalloc(struct_size(req, buf, len), GFP_ATOMIC);
if (!req)
return -ENOMEM;

--
2.34.1