Merge pull request #1772 from pchaigno/limit-rewrites-from-ctx

Limit dereference rewriter to tracing contexts

src/cc/frontends/clang/b_frontend_action.cc

@@ -911,7 +911,16 @@ void BTypeConsumer::HandleTranslationUnit(ASTContext &Context) {
       if (fe_.is_rewritable_ext_func(F)) {
         for (auto arg : F->parameters()) {
           if (arg == F->getParamDecl(0)) {
-            probe_visitor1_.set_ctx(arg);
+            /**
+             * Limit tracing of pointers from context to tracing contexts.
+             * We're whitelisting instead of blacklisting to avoid issues with
+             * existing programs if new context types are added in the future.
+             */
+            string type = arg->getType().getAsString();
+            if (type == "struct pt_regs *" ||
+                type == "struct bpf_raw_tracepoint_args *" ||
+                type.substr(0, 19) == "struct tracepoint__")
+              probe_visitor1_.set_ctx(arg);
           } else if (!arg->getType()->isFundamentalType()) {
             probe_visitor1_.set_ptreg(arg);
           }

tests/python/test_clang.py

@@ -810,6 +810,25 @@ int test(struct pt_regs *ctx) {
         b = BPF(text=text)
         fn = b.load_func("test", BPF.KPROBE)
 
+    @skipUnless(kernel_version_ge(4,7), "requires kernel >= 4.7")
+    def test_probe_read_tc_ctx(self):
+        text = """
+#include <uapi/linux/pkt_cls.h>
+#include <linux/if_ether.h>
+int test(struct __sk_buff *ctx) {
+    void* data_end = (void*)(long)ctx->data_end;
+    void* data = (void*)(long)ctx->data;
+    if (data + sizeof(struct ethhdr) > data_end)
+        return TC_ACT_SHOT;
+    struct ethhdr *eh = (struct ethhdr *)data;
+    if (eh->h_proto == 0x1)
+        return TC_ACT_SHOT;
+    return TC_ACT_OK;
+}
+"""
+        b = BPF(text=text)
+        fn = b.load_func("test", BPF.SCHED_CLS)
+
 
 if __name__ == "__main__":
     main()