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Subject[PATCH v2 2/2] net: socket: implement SO_DESCRIPTION
Date
This command attaches the zero terminated string in optval to the
socket for troubleshooting purposes. The free string is displayed in the
process fdinfo file for that fd (/proc/<pid>/fdinfo/<fd>).

One intended usage is to allow processes to self-document sockets
for netstat and friends to report

We ignore optlen and constrain the string to a static max size

Signed-off-by: Pascal Bouchareine <kalou@tfz.net>
---
include/net/sock.h | 4 +++
include/uapi/asm-generic/socket.h | 2 ++
net/core/sock.c | 53 +++++++++++++++++++++++++++++++
net/socket.c | 5 +++
4 files changed, 64 insertions(+)

diff --git a/include/net/sock.h b/include/net/sock.h
index 1183507df95b..6b4fd1383282 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -342,6 +342,7 @@ struct bpf_sk_storage;
* @sk_txtime_deadline_mode: set deadline mode for SO_TXTIME
* @sk_txtime_report_errors: set report errors mode for SO_TXTIME
* @sk_txtime_unused: unused txtime flags
+ * @sk_description: user supplied with SO_DESCRIPTION
*/
struct sock {
/*
@@ -519,6 +520,9 @@ struct sock {
struct bpf_sk_storage __rcu *sk_bpf_storage;
#endif
struct rcu_head sk_rcu;
+
+#define SK_MAX_DESC_SIZE 256
+ char *sk_description;
};

enum sk_pacing {
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index 77f7c1638eb1..fb51c4bb7a12 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -119,6 +119,8 @@

#define SO_DETACH_REUSEPORT_BPF 68

+#define SO_DESCRIPTION 69
+
#if !defined(__KERNEL__)

#if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
diff --git a/net/core/sock.c b/net/core/sock.c
index 2e5b7870e5d3..b8bad57338d8 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -828,6 +828,49 @@ void sock_set_rcvbuf(struct sock *sk, int val)
}
EXPORT_SYMBOL(sock_set_rcvbuf);

+static int sock_set_description(struct sock *sk, char __user *user_desc)
+{
+ char *old, *desc;
+
+ desc = strndup_user(user_desc, SK_MAX_DESC_SIZE, GFP_KERNEL_ACCOUNT);
+ if (IS_ERR(desc))
+ return PTR_ERR(desc);
+
+ lock_sock(sk);
+ old = sk->sk_description;
+ sk->sk_description = desc;
+ release_sock(sk);
+
+ kfree(old);
+
+ return 0;
+}
+
+static int sock_get_description(struct sock *sk, char __user *optval,
+ int __user *optlen, int len)
+{
+ char desc[SK_MAX_DESC_SIZE];
+
+ lock_sock(sk);
+ if (sk->sk_description) {
+ /* strndup_user: len(desc + nul) <= SK_MAX_DESC_SIZE */
+ len = min_t(unsigned int, len,
+ strlen(sk->sk_description) + 1);
+ memcpy(desc, sk->sk_description, len);
+ } else {
+ len = 0;
+ }
+ release_sock(sk);
+
+ if (copy_to_user(optval, desc, len))
+ return -EFAULT;
+
+ if (put_user(len, optlen))
+ return -EFAULT;
+
+ return 0;
+}
+
/*
* This is meant for all protocols to use and covers goings on
* at the socket level. Everything here is generic.
@@ -850,6 +893,9 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
if (optname == SO_BINDTODEVICE)
return sock_setbindtodevice(sk, optval, optlen);

+ if (optname == SO_DESCRIPTION)
+ return sock_set_description(sk, optval);
+
if (optlen < sizeof(int))
return -EINVAL;

@@ -1614,6 +1660,9 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
v.val = sk->sk_bound_dev_if;
break;

+ case SO_DESCRIPTION:
+ return sock_get_description(sk, optval, optlen, len);
+
default:
/* We implement the SO_SNDLOWAT etc to not be settable
* (1003.1g 7).
@@ -1792,6 +1841,8 @@ static void __sk_destruct(struct rcu_head *head)
RCU_INIT_POINTER(sk->sk_filter, NULL);
}

+ kfree(sk->sk_description);
+
sock_disable_timestamp(sk, SK_FLAGS_TIMESTAMP);

#ifdef CONFIG_BPF_SYSCALL
@@ -1964,6 +2015,8 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
if (sk_user_data_is_nocopy(newsk))
newsk->sk_user_data = NULL;

+ newsk->sk_description = NULL;
+
newsk->sk_err = 0;
newsk->sk_err_soft = 0;
newsk->sk_priority = 0;
diff --git a/net/socket.c b/net/socket.c
index 976426d03f09..4f2c1a7744b0 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -134,6 +134,11 @@ static void sock_show_fdinfo(struct seq_file *m, struct file *f)
{
struct socket *sock = f->private_data;

+ lock_sock(sock->sk);
+ if (sock->sk->sk_description)
+ seq_printf(m, "desc:\t%s\n", sock->sk->sk_description);
+ release_sock(sock->sk);
+
if (sock->ops->show_fdinfo)
sock->ops->show_fdinfo(m, sock);
}
--
2.25.1
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