Merge branch 'setsockopt-extra-mem'

Stanislav Fomichev says:

====================
Current setsockopt hook is limited to the size of the buffer that
user had supplied. Since we always allocate memory and copy the value
into kernel space, allocate just a little bit more in case BPF
program needs to override input data with a larger value.

The canonical example is TCP_CONGESTION socket option where
input buffer is a string and if user calls it with a short string,
BPF program has no way of extending it.

The tests are extended with TCP_CONGESTION use case.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 47 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/sockopt_sk.c b/tools/testing/selftests/bpf/progs/sockopt_sk.c
index 076122c898e9..9a3d1c79e6fe 100644
--- a/tools/testing/selftests/bpf/progs/sockopt_sk.c
+++ b/tools/testing/selftests/bpf/progs/sockopt_sk.c
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <string.h>
 #include <netinet/in.h>
+#include <netinet/tcp.h>
 #include <linux/bpf.h>
 #include "bpf_helpers.h"
 
@@ -42,6 +44,14 @@ int _getsockopt(struct bpf_sockopt *ctx)
 		return 1;
 	}
 
+	if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) {
+		/* Not interested in SOL_TCP:TCP_CONGESTION;
+		 * let next BPF program in the cgroup chain or kernel
+		 * handle it.
+		 */
+		return 1;
+	}
+
 	if (ctx->level != SOL_CUSTOM)
 		return 0; /* EPERM, deny everything except custom level */
 
@@ -91,6 +101,18 @@ int _setsockopt(struct bpf_sockopt *ctx)
 		return 1;
 	}
 
+	if (ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION) {
+		/* Always use cubic */
+
+		if (optval + 5 > optval_end)
+			return 0; /* EPERM, bounds check */
+
+		memcpy(optval, "cubic", 5);
+		ctx->optlen = 5;
+
+		return 1;
+	}
+
 	if (ctx->level != SOL_CUSTOM)
 		return 0; /* EPERM, deny everything except custom level */
 
diff --git a/tools/testing/selftests/bpf/test_sockopt_sk.c b/tools/testing/selftests/bpf/test_sockopt_sk.c
index 036b652e5ca9..e4f6055d92e9 100644
--- a/tools/testing/selftests/bpf/test_sockopt_sk.c
+++ b/tools/testing/selftests/bpf/test_sockopt_sk.c
@@ -6,6 +6,7 @@
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
+#include <netinet/tcp.h>
 
 #include <linux/filter.h>
 #include <bpf/bpf.h>
@@ -25,6 +26,7 @@ static int getsetsockopt(void)
 	union {
 		char u8[4];
 		__u32 u32;
+		char cc[16]; /* TCP_CA_NAME_MAX */
 	} buf = {};
 	socklen_t optlen;
 
@@ -115,6 +117,29 @@ static int getsetsockopt(void)
 		goto err;
 	}
 
+	/* TCP_CONGESTION can extend the string */
+
+	strcpy(buf.cc, "nv");
+	err = setsockopt(fd, SOL_TCP, TCP_CONGESTION, &buf, strlen("nv"));
+	if (err) {
+		log_err("Failed to call setsockopt(TCP_CONGESTION)");
+		goto err;
+	}
+
+
+	optlen = sizeof(buf.cc);
+	err = getsockopt(fd, SOL_TCP, TCP_CONGESTION, &buf, &optlen);
+	if (err) {
+		log_err("Failed to call getsockopt(TCP_CONGESTION)");
+		goto err;
+	}
+
+	if (strcmp(buf.cc, "cubic") != 0) {
+		log_err("Unexpected getsockopt(TCP_CONGESTION) %s != %s",
+			buf.cc, "cubic");
+		goto err;
+	}
+
 	close(fd);
 	return 0;
 err: