iommu/virtio: Add __counted_by for struct viommu_request and use struct_size()

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>
Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Reviewed-by: Justin Stitt <justinstitt@google.com>
Link: https://lore.kernel.org/r/ZSRFW0yDlDo8+at3@work
Signed-off-by: Joerg Roedel <jroedel@suse.de>

diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
index 17dcd826f5c20e16b62daf837c2dc88ad5275d5f..379ebe03efb6d45b42afd8a63b4fcb830bb37903 100644 (file)
--- 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;