netdev - [PATCH bpf] bpf: Fix bpf_sk_select

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Message-Id: <20250110-reuseport-memleak-v1-1-fa1ddab0adfe@rbox.co>
Date: Fri, 10 Jan 2025 14:21:55 +0100
From: Michal Luczaj <mhal@...x.co>
To: Alexei Starovoitov <ast@...nel.org>, 
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
 Martin KaFai Lau <martin.lau@...ux.dev>, 
 Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
 Yonghong Song <yonghong.song@...ux.dev>, 
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, 
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
 Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>, 
 Shuah Khan <shuah@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 Jakub Sitnicki <jakub@...udflare.com>
Cc: bpf@...r.kernel.org, netdev@...r.kernel.org, 
 Michal Luczaj <mhal@...x.co>
Subject: [PATCH bpf] bpf: Fix bpf_sk_select_reuseport() memory leak

As pointed out in the original comment, lookup in sockmap can return a TCP
ESTABLISHED socket. Such TCP socket may have had SO_ATTACH_REUSEPORT_EBPF
set before it was ESTABLISHED. In other words, a non-NULL sk_reuseport_cb
does not imply a non-refcounted socket.

Drop sk's reference in both error paths.

unreferenced object 0xffff888101911800 (size 2048):
  comm "test_progs", pid 44109, jiffies 4297131437
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    80 00 01 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace (crc 9336483b):
    __kmalloc_noprof+0x3bf/0x560
    __reuseport_alloc+0x1d/0x40
    reuseport_alloc+0xca/0x150
    reuseport_attach_prog+0x87/0x140
    sk_reuseport_attach_bpf+0xc8/0x100
    sk_setsockopt+0x1181/0x1990
    do_sock_setsockopt+0x12b/0x160
    __sys_setsockopt+0x7b/0xc0
    __x64_sys_setsockopt+0x1b/0x30
    do_syscall_64+0x93/0x180
    entry_SYSCALL_64_after_hwframe+0x76/0x7e

Fixes: 64d85290d79c ("bpf: Allow bpf_map_lookup_elem for SOCKMAP and SOCKHASH")
Signed-off-by: Michal Luczaj <mhal@...x.co>
---
 net/core/filter.c | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 834614071727ab92cee759dc788ec2ee6f92284b..2fb45a86f3ddbffa9fd55885d4c4c0d8c3a6c381 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -11251,6 +11251,7 @@ BPF_CALL_4(sk_select_reuseport, struct sk_reuseport_kern *, reuse_kern,
 	bool is_sockarray = map->map_type == BPF_MAP_TYPE_REUSEPORT_SOCKARRAY;
 	struct sock_reuseport *reuse;
 	struct sock *selected_sk;
+	int err;
 
 	selected_sk = map->ops->map_lookup_elem(map, key);
 	if (!selected_sk)
@@ -11258,10 +11259,6 @@ BPF_CALL_4(sk_select_reuseport, struct sk_reuseport_kern *, reuse_kern,
 
 	reuse = rcu_dereference(selected_sk->sk_reuseport_cb);
 	if (!reuse) {
-		/* Lookup in sock_map can return TCP ESTABLISHED sockets. */
-		if (sk_is_refcounted(selected_sk))
-			sock_put(selected_sk);
-
 		/* reuseport_array has only sk with non NULL sk_reuseport_cb.
 		 * The only (!reuse) case here is - the sk has already been
 		 * unhashed (e.g. by close()), so treat it as -ENOENT.
@@ -11269,24 +11266,33 @@ BPF_CALL_4(sk_select_reuseport, struct sk_reuseport_kern *, reuse_kern,
 		 * Other maps (e.g. sock_map) do not provide this guarantee and
 		 * the sk may never be in the reuseport group to begin with.
 		 */
-		return is_sockarray ? -ENOENT : -EINVAL;
+		err = is_sockarray ? -ENOENT : -EINVAL;
+		goto error;
 	}
 
 	if (unlikely(reuse->reuseport_id != reuse_kern->reuseport_id)) {
 		struct sock *sk = reuse_kern->sk;
 
-		if (sk->sk_protocol != selected_sk->sk_protocol)
-			return -EPROTOTYPE;
-		else if (sk->sk_family != selected_sk->sk_family)
-			return -EAFNOSUPPORT;
-
-		/* Catch all. Likely bound to a different sockaddr. */
-		return -EBADFD;
+		if (sk->sk_protocol != selected_sk->sk_protocol) {
+			err = -EPROTOTYPE;
+		} else if (sk->sk_family != selected_sk->sk_family) {
+			err = -EAFNOSUPPORT;
+		} else {
+			/* Catch all. Likely bound to a different sockaddr. */
+			err = -EBADFD;
+		}
+		goto error;
 	}
 
 	reuse_kern->selected_sk = selected_sk;
 
 	return 0;
+error:
+	/* Lookup in sock_map can return TCP ESTABLISHED sockets. */
+	if (sk_is_refcounted(selected_sk))
+		sock_put(selected_sk);
+
+	return err;
 }
 
 static const struct bpf_func_proto sk_select_reuseport_proto = {

---
base-commit: 1f6ff8756091d99b7e5fa556abc0465328302b8b
change-id: 20250110-reuseport-memleak-9ac6587bd99a

Best regards,
-- 
Michal Luczaj <mhal@...x.co>