netdev - [PATCH v2] net/af_unix: don't create a path for a binded socket

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Message-Id: <20201130132747.29332-1-kda@linux-powerpc.org>
Date:   Mon, 30 Nov 2020 16:27:47 +0300
From:   Denis Kirjanov <kda@...ux-powerpc.org>
To:     netdev@...r.kernel.org
Cc:     kuba@...nel.org, davem@...emloft.net
Subject: [PATCH v2] net/af_unix: don't create a path for a binded socket

in the case of the socket which is bound to an adress
there is no sense to create a path in the next attempts

here is a program that shows the issue:

int main()
{
    int s;
    struct sockaddr_un a;

    s = socket(AF_UNIX, SOCK_STREAM, 0);
    if (s<0)
        perror("socket() failed\n");

    printf("First bind()\n");

    memset(&a, 0, sizeof(a));
    a.sun_family = AF_UNIX;
    strncpy(a.sun_path, "/tmp/.first_bind", sizeof(a.sun_path));

    if ((bind(s, (const struct sockaddr*) &a, sizeof(a))) == -1)
        perror("bind() failed\n");

    printf("Second bind()\n");

    memset(&a, 0, sizeof(a));
    a.sun_family = AF_UNIX;
    strncpy(a.sun_path, "/tmp/.first_bind_failed", sizeof(a.sun_path));

    if ((bind(s, (const struct sockaddr*) &a, sizeof(a))) == -1)
        perror("bind() failed\n");
}

kda@...S15-SP2:~> ./test
First bind()
Second bind()
bind() failed
: Invalid argument

kda@...S15-SP2:~> ls -la /tmp/.first_bind
.first_bind         .first_bind_failed

Signed-off-by: Denis Kirjanov <kda@...ux-powerpc.org>

v2: move a new patch creation after the address assignment check.
---
 net/unix/af_unix.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 41c3303c3357..ff2dd1d3536b 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1034,6 +1034,14 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 		goto out;
 	addr_len = err;
 
+	err = mutex_lock_interruptible(&u->bindlock);
+	if (err)
+		goto out_put;
+
+	err = -EINVAL;
+	if (u->addr)
+		goto out_up;
+
 	if (sun_path[0]) {
 		umode_t mode = S_IFSOCK |
 		       (SOCK_INODE(sock)->i_mode & ~current_umask());
@@ -1045,14 +1053,6 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 		}
 	}
 
-	err = mutex_lock_interruptible(&u->bindlock);
-	if (err)
-		goto out_put;
-
-	err = -EINVAL;
-	if (u->addr)
-		goto out_up;
-
 	err = -ENOMEM;
 	addr = kmalloc(sizeof(*addr)+addr_len, GFP_KERNEL);
 	if (!addr)
-- 
2.16.4