selftests/net: mptcp: fix uninitialized variable warnings

Same init_rng() in both tests. The function reads /dev/urandom to
initialize srand(). In case of failure, it falls back onto the
entropy in the uninitialized variable. Not sure if this is on purpose.
But failure reading urandom should be rare, so just fail hard. While
at it, convert to getrandom(). Which man 4 random suggests is simpler
and more robust.

    mptcp_inq.c:525:6:
    mptcp_connect.c:1131:6:

    error: variable 'foo' is used uninitialized
    whenever 'if' condition is false
    [-Werror,-Wsometimes-uninitialized]

Fixes: 048d19d444be ("mptcp: add basic kselftest for mptcp")
Fixes: b51880568f20 ("selftests: mptcp: add inq test case")
Cc: Florian Westphal <fw@strlen.de>
Signed-off-by: Willem de Bruijn <willemb@google.com>

----

When input is randomized because this is expected to meaningfully
explore edge cases, should we also add
1. logging the random seed to stdout and
2. adding a command line argument to replay from a specific seed
I can do this in net-next, if authors find it useful in this case.
Reviewed-by: Matthieu Baerts <matttbe@kernel.org>

Link: https://lore.kernel.org/r/20231124171645.1011043-5-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 8 insertions, 14 deletions

diff --git a/tools/testing/selftests/net/mptcp/mptcp_connect.c b/tools/testing/selftests/net/mptcp/mptcp_connect.c
index c7f9ebeebc2c..d2043ec3bf6d 100644
--- a/tools/testing/selftests/net/mptcp/mptcp_connect.c
+++ b/tools/testing/selftests/net/mptcp/mptcp_connect.c
@@ -18,6 +18,7 @@
 
 #include <sys/ioctl.h>
 #include <sys/poll.h>
+#include <sys/random.h>
 #include <sys/sendfile.h>
 #include <sys/stat.h>
 #include <sys/socket.h>
@@ -1125,15 +1126,11 @@ again:
 
 static void init_rng(void)
 {
-	int fd = open("/dev/urandom", O_RDONLY);
 	unsigned int foo;
 
-	if (fd > 0) {
-		int ret = read(fd, &foo, sizeof(foo));
-
-		if (ret < 0)
-			srand(fd + foo);
-		close(fd);
+	if (getrandom(&foo, sizeof(foo), 0) == -1) {
+		perror("getrandom");
+		exit(1);
 	}
 
 	srand(foo);
diff --git a/tools/testing/selftests/net/mptcp/mptcp_inq.c b/tools/testing/selftests/net/mptcp/mptcp_inq.c
index 8672d898f8cd..218aac467321 100644
--- a/tools/testing/selftests/net/mptcp/mptcp_inq.c
+++ b/tools/testing/selftests/net/mptcp/mptcp_inq.c
@@ -18,6 +18,7 @@
 #include <time.h>
 
 #include <sys/ioctl.h>
+#include <sys/random.h>
 #include <sys/socket.h>
 #include <sys/types.h>
 #include <sys/wait.h>
@@ -519,15 +520,11 @@ static int client(int unixfd)
 
 static void init_rng(void)
 {
-	int fd = open("/dev/urandom", O_RDONLY);
 	unsigned int foo;
 
-	if (fd > 0) {
-		int ret = read(fd, &foo, sizeof(foo));
-
-		if (ret < 0)
-			srand(fd + foo);
-		close(fd);
+	if (getrandom(&foo, sizeof(foo), 0) == -1) {
+		perror("getrandom");
+		exit(1);
 	}
 
 	srand(foo);