[PATCH bpf-next 2/2] selftest/bpf: Ensure no module loading in bpf_setsockopt(TCP_CONGESTION)

[Martin KaFai Lau <martin.lau@linux.dev>]

This patch adds a test to ensure
bpf_setsockopt(TCP_CONGESTION, "not_exist")
will not trigger the kernel module autoload.

Before the fix:
[   40.535829] BUG: sleeping function called from invalid context at include/linux/sched/mm.h:274
...
[   40.552134]  tcp_ca_find_autoload.constprop.0+0xcb/0x200
[   40.552689]  tcp_set_congestion_control+0x99/0x7b0
[   40.553203]  do_tcp_setsockopt+0x3ed/0x2240
...
[   40.556041]  __bpf_setsockopt+0x124/0x640

Signed-off-by: Martin KaFai Lau <martin.lau@linux.dev>
---
 tools/testing/selftests/bpf/progs/setget_sockopt.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/setget_sockopt.c b/tools/testing/selftests/bpf/progs/setget_sockopt.c
index 40606ef47a38..79debf3c2f44 100644
--- a/tools/testing/selftests/bpf/progs/setget_sockopt.c
+++ b/tools/testing/selftests/bpf/progs/setget_sockopt.c
@@ -32,6 +32,7 @@ struct sockopt_test {
 	unsigned int flip:1;
 };
 
+static const char not_exist_cc[] = "not_exist";
 static const char cubic_cc[] = "cubic";
 static const char reno_cc[] = "reno";
 
@@ -307,6 +308,9 @@ static int bpf_test_tcp_sockopt(__u32 i, struct loop_ctx *lc)
 		const char *new_cc;
 		int new_cc_len;
 
+		if (!bpf_setsockopt(ctx, IPPROTO_TCP, TCP_CONGESTION,
+				    (void *)not_exist_cc, sizeof(not_exist_cc)))
+			return 1;
 		if (bpf_getsockopt(ctx, IPPROTO_TCP, TCP_CONGESTION, old_cc, sizeof(old_cc)))
 			return 1;
 		if (!bpf_strncmp(old_cc, sizeof(old_cc), cubic_cc)) {
-- 
2.30.2