[PATCH bpf-next v2] selftests/bpf: fix signedness bug in redir_partial()

[Fushuai Wang]

When xsend() returns -1 (error), the check 'n < sizeof(buf)' incorrectly
treats it as success due to unsigned promotion. Explicitly check for -1
first.

Fixes: a4b7193d8efd ("selftests/bpf: Add sockmap test for redirecting partial skb data")
Signed-off-by: Fushuai Wang <wangfushuai@xxxxxxxxx>
---
 tools/testing/selftests/bpf/prog_tests/sockmap_listen.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_listen.c b/tools/testing/selftests/bpf/prog_tests/sockmap_listen.c
index 1d98eee7a2c3..f1bdccc7e4e7 100644
--- a/tools/testing/selftests/bpf/prog_tests/sockmap_listen.c
+++ b/tools/testing/selftests/bpf/prog_tests/sockmap_listen.c
@@ -924,6 +924,8 @@ static void redir_partial(int family, int sotype, int sock_map, int parser_map)
 		goto close;
 
 	n = xsend(c1, buf, sizeof(buf), 0);
+	if (n == -1)
+		goto close;
 	if (n < sizeof(buf))
 		FAIL("incomplete write");
 
-- 
2.36.1