bpf: Refuse unused attributes in bpf_prog_{attach,detach}

The recently added tcx attachment extended the BPF UAPI for attaching and
detaching by a couple of fields. Those fields are currently only supported
for tcx, other types like cgroups and flow dissector silently ignore the
new flags.

This is problematic once we extend bpf_mprog to older attachment types, since
it's hard to figure out whether the syscall really was successful if the
kernel silently ignores non-zero values.

Explicitly reject non-zero flags for attachment types which don't use
bpf_mprog yet.

Independent of this, we were also thinking about rejecting attr->replace_bpf_fd
for the bpf_prog_detach() case given this is not used there generally. However,
this field has been ignored in detach for several releases, thus rejecting
has a risk of potential breakage.

Fixes: e420bed ("bpf: Add fd-based tcx multi-prog infra with link support")
Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
Co-developed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

kernel/bpf/syscall.c

@@ -3796,7 +3796,6 @@ static int bpf_prog_attach(const union bpf_attr *attr)
 {
 	enum bpf_prog_type ptype;
 	struct bpf_prog *prog;
-	u32 mask;
 	int ret;
 
 	if (CHECK_ATTR(BPF_PROG_ATTACH))
@@ -3805,10 +3804,16 @@ static int bpf_prog_attach(const union bpf_attr *attr)
 	ptype = attach_type_to_prog_type(attr->attach_type);
 	if (ptype == BPF_PROG_TYPE_UNSPEC)
 		return -EINVAL;
-	mask = bpf_mprog_supported(ptype) ?
-	       BPF_F_ATTACH_MASK_MPROG : BPF_F_ATTACH_MASK_BASE;
-	if (attr->attach_flags & ~mask)
-		return -EINVAL;
+	if (bpf_mprog_supported(ptype)) {
+		if (attr->attach_flags & ~BPF_F_ATTACH_MASK_MPROG)
+			return -EINVAL;
+	} else {
+		if (attr->attach_flags & ~BPF_F_ATTACH_MASK_BASE)
+			return -EINVAL;
+		if (attr->relative_fd ||
+		    attr->expected_revision)
+			return -EINVAL;
+	}
 
 	prog = bpf_prog_get_type(attr->attach_bpf_fd, ptype);
 	if (IS_ERR(prog))
@@ -3878,6 +3883,10 @@ static int bpf_prog_detach(const union bpf_attr *attr)
 			if (IS_ERR(prog))
 				return PTR_ERR(prog);
 		}
+	} else if (attr->attach_flags ||
+		   attr->relative_fd ||
+		   attr->expected_revision) {
+		return -EINVAL;
 	}
 
 	switch (ptype) {