The VhostUserMsg struct binary representation must match the vhost-user
protocol specification since this struct is read from and written to the
socket.
The VhostUserMsg.request union contains enum fields. Enum binary
representation is implementation-defined according to the C standard and
it is unportable to make assumptions about the representation:
6.7.2.2 Enumeration specifiers
...
Each enumerated type shall be compatible with char, a signed integer
type, or an unsigned integer type. The choice of type is
implementation-defined, but shall be capable of representing the
values of all the members of the enumeration.
Additionally, librte_vhost relies on the enum type being unsigned when
validating untrusted inputs:
if (ret <= 0 || msg.request.master >= VHOST_USER_MAX) {
If msg.request.master is signed then negative values pass this check!
Even if we assume gcc on x86_64 (SysV amd64 ABI) and don't care about
portability, the actual enum constants still affect the final type. For
example, if we add a negative constant then its type changes to signed
int:
typedef enum VhostUserRequest {
...
VHOST_USER_INVALID = -1,
};
This is very fragile and it's unlikely that anyone changing the code
would remember this. A security hole can be introduced accidentally.
This patch switches VhostUserMsg.request fields to uint32_t to avoid the
portability and potential security issues.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
cdc37ca3d0