[PATCH bpf 4/4] selftests/bpf: test for changing packet data from global functions

[Eduard Zingerman <eddyz87@gmail.com>]

Check if verifier is aware of packet pointers invalidation done in
global functions. Based on a test shared by Nick Zavaritsky in [0].

[0] https://lore.kernel.org/bpf/0498CA22-5779-4767-9C0C-A9515CEA711F@gmail.com/

Suggested-by: Nick Zavaritsky <mejedi@gmail.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
 .../selftests/bpf/progs/verifier_sock.c       | 28 +++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_sock.c b/tools/testing/selftests/bpf/progs/verifier_sock.c
index d3e70e38e442..51826379a1aa 100644
--- a/tools/testing/selftests/bpf/progs/verifier_sock.c
+++ b/tools/testing/selftests/bpf/progs/verifier_sock.c
@@ -1037,4 +1037,32 @@ __naked void sock_create_read_src_port(void)
 	: __clobber_all);
 }
 
+__noinline
+long skb_pull_data2(struct __sk_buff *sk, __u32 len)
+{
+	return bpf_skb_pull_data(sk, len);
+}
+
+__noinline
+long skb_pull_data1(struct __sk_buff *sk, __u32 len)
+{
+	return skb_pull_data2(sk, len);
+}
+
+/* global function calls bpf_skb_pull_data(), which invalidates packet
+ * pointers established before global function call.
+ */
+SEC("tc")
+__failure __msg("invalid mem access")
+int invalidate_pkt_pointers_from_global_func(struct __sk_buff *sk)
+{
+	int *p = (void *)(long)sk->data;
+
+	if ((void *)(p + 1) > (void *)(long)sk->data_end)
+		return TCX_DROP;
+	skb_pull_data1(sk, 0);
+	*p = 42; /* this is unsafe */
+	return TCX_PASS;
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.47.0