[PATCH net 10/12] net: shaper: reject handle IDs exceeding internal bit-width

[Jakub Kicinski <kuba@kernel.org>]

net_shaper_parse_handle() reads the user-supplied handle ID via
nla_get_u32(), accepting the full u32 range. However, the xarray key
is built by net_shaper_handle_to_index() using
FIELD_PREP(NET_SHAPER_ID_MASK, handle->id), where NET_SHAPER_ID_MASK
is GENMASK(25, 0) - only 26 bits wide. FIELD_PREP silently masks off
the upper bits at runtime. A user-supplied NODE id like 0x04000123
becomes id 0x123.

Additionally, a user-supplied id equal to NET_SHAPER_ID_UNSPEC
(0x03FFFFFF, which is NET_SHAPER_ID_MASK itself) would collide with
the sentinel used internally by the group operation to signal
"allocate a new NODE id".

Reject user-supplied IDs >= NET_SHAPER_ID_MASK (i.e., >= 0x03FFFFFF)
in the policy.

Fixes: 4b623f9f0f59 ("net-shapers: implement NL get operation")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 Documentation/netlink/specs/net_shaper.yaml | 7 +++++++
 net/shaper/shaper_nl_gen.h                  | 2 ++
 net/shaper/shaper.c                         | 4 +++-
 net/shaper/shaper_nl_gen.c                  | 7 ++++++-
 4 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/Documentation/netlink/specs/net_shaper.yaml b/Documentation/netlink/specs/net_shaper.yaml
index 3f2ad772b64b..de01f922040a 100644
--- a/Documentation/netlink/specs/net_shaper.yaml
+++ b/Documentation/netlink/specs/net_shaper.yaml
@@ -33,6 +33,11 @@ doc: |
   @cap-get operation.
 
 definitions:
+  -
+    type: const
+    name: max-handle-id
+    value: 0x3fffffe
+    scope: kernel
   -
     type: enum
     name: scope
@@ -140,6 +145,8 @@ doc: |
       -
         name: id
         type: u32
+        checks:
+          max: max-handle-id
         doc: |
           Numeric identifier of a shaper. The id semantic depends on
           the scope. For @queue scope it's the queue id and for @node
diff --git a/net/shaper/shaper_nl_gen.h b/net/shaper/shaper_nl_gen.h
index 42c46c52c775..2406652a9014 100644
--- a/net/shaper/shaper_nl_gen.h
+++ b/net/shaper/shaper_nl_gen.h
@@ -12,6 +12,8 @@
 
 #include <uapi/linux/net_shaper.h>
 
+#define NET_SHAPER_MAX_HANDLE_ID	67108862
+
 /* Common nested types */
 extern const struct nla_policy net_shaper_handle_nl_policy[NET_SHAPER_A_HANDLE_ID + 1];
 extern const struct nla_policy net_shaper_leaf_info_nl_policy[NET_SHAPER_A_WEIGHT + 1];
diff --git a/net/shaper/shaper.c b/net/shaper/shaper.c
index 10d76f7148bf..16bf24d9e3ca 100644
--- a/net/shaper/shaper.c
+++ b/net/shaper/shaper.c
@@ -21,6 +21,8 @@
 
 #define NET_SHAPER_ID_UNSPEC NET_SHAPER_ID_MASK
 
+static_assert(NET_SHAPER_ID_UNSPEC == NET_SHAPER_MAX_HANDLE_ID + 1);
+
 struct net_shaper_hierarchy {
 	struct xarray shapers;
 };
@@ -360,7 +362,7 @@ static int net_shaper_pre_insert(struct net_shaper_binding *binding,
 	    handle->id == NET_SHAPER_ID_UNSPEC) {
 		u32 min, max;
 
-		handle->id = NET_SHAPER_ID_MASK - 1;
+		handle->id = NET_SHAPER_MAX_HANDLE_ID;
 		max = net_shaper_handle_to_index(handle);
 		handle->id = 0;
 		min = net_shaper_handle_to_index(handle);
diff --git a/net/shaper/shaper_nl_gen.c b/net/shaper/shaper_nl_gen.c
index 9b29be3ef19a..76eff85ec66d 100644
--- a/net/shaper/shaper_nl_gen.c
+++ b/net/shaper/shaper_nl_gen.c
@@ -11,10 +11,15 @@
 
 #include <uapi/linux/net_shaper.h>
 
+/* Integer value ranges */
+static const struct netlink_range_validation net_shaper_a_handle_id_range = {
+	.max	= NET_SHAPER_MAX_HANDLE_ID,
+};
+
 /* Common nested types */
 const struct nla_policy net_shaper_handle_nl_policy[NET_SHAPER_A_HANDLE_ID + 1] = {
 	[NET_SHAPER_A_HANDLE_SCOPE] = NLA_POLICY_MAX(NLA_U32, 3),
-	[NET_SHAPER_A_HANDLE_ID] = { .type = NLA_U32, },
+	[NET_SHAPER_A_HANDLE_ID] = NLA_POLICY_FULL_RANGE(NLA_U32, &net_shaper_a_handle_id_range),
 };
 
 const struct nla_policy net_shaper_leaf_info_nl_policy[NET_SHAPER_A_WEIGHT + 1] = {
-- 
2.54.0