virtchnl: fix fake 1-elem arrays in structs allocated as `nents + 1` - 1

The two most problematic virtchnl structures are virtchnl_rss_key and
virtchnl_rss_lut. Their "flex" arrays have the type of u8, thus, when
allocating / checking, the actual size is calculated as `sizeof +
nents - 1 byte`. But their sizeof() is not 1 byte larger than the size
of such structure with proper flex array, it's two bytes larger due to
the padding. That said, their size is always 1 byte larger unless
there are no tail elements -- then it's +2 bytes.
Add virtchnl_struct_size() macro which will handle this case (and later
other cases as well). Make its calling conv the same as we call
struct_size() to allow it to be drop-in, even though it's unlikely to
become possible to switch to generic API. The macro will calculate a
proper size of a structure with a flex array at the end, so that it
becomes transparent for the compilers, but add the difference from the
old values, so that the real size of sorta-ABI-messages doesn't change.
Use it on the allocation side in IAVF and the receiving side (defined
as static inline in virtchnl.h) for the mentioned two structures.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

1 files changed, 2 insertions, 4 deletions

diff --git a/drivers/net/ethernet/intel/iavf/iavf_virtchnl.c b/drivers/net/ethernet/intel/iavf/iavf_virtchnl.c
index be3c007ce90a..10f03054a603 100644
--- a/drivers/net/ethernet/intel/iavf/iavf_virtchnl.c
+++ b/drivers/net/ethernet/intel/iavf/iavf_virtchnl.c
@@ -1085,8 +1085,7 @@ void iavf_set_rss_key(struct iavf_adapter *adapter)
 			adapter->current_op);
 		return;
 	}
-	len = sizeof(struct virtchnl_rss_key) +
-	      (adapter->rss_key_size * sizeof(u8)) - 1;
+	len = virtchnl_struct_size(vrk, key, adapter->rss_key_size);
 	vrk = kzalloc(len, GFP_KERNEL);
 	if (!vrk)
 		return;
@@ -1117,8 +1116,7 @@ void iavf_set_rss_lut(struct iavf_adapter *adapter)
 			adapter->current_op);
 		return;
 	}
-	len = sizeof(struct virtchnl_rss_lut) +
-	      (adapter->rss_lut_size * sizeof(u8)) - 1;
+	len = virtchnl_struct_size(vrl, lut, adapter->rss_lut_size);
 	vrl = kzalloc(len, GFP_KERNEL);
 	if (!vrl)
 		return;