[PATCH v3] net/af_unix: don't create a path for a binded socket

[PATCH v3] net/af_unix: don't create a path for a binded socket

[Denis Kirjanov]

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@SLES15-SP2:~> ./test
First bind()
Second bind()
bind() failed
: Invalid argument

kda@SLES15-SP2:~> ls -la /tmp/.first_bind
.first_bind         .first_bind_failed

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

v2: move a new path creation after the address assignment check
v3: fixed goto labels on the error path
---
 net/unix/af_unix.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 41c3303c3357..70861e9bcfd9 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;
+
+	err = -EINVAL;
+	if (u->addr)
+		goto out_up;
+
 	if (sun_path[0]) {
 		umode_t mode = S_IFSOCK |
 		       (SOCK_INODE(sock)->i_mode & ~current_umask());
@@ -1041,22 +1049,14 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 		if (err) {
 			if (err == -EEXIST)
 				err = -EADDRINUSE;
-			goto out;
+			goto out_up;
 		}
 	}
 
-	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)
-		goto out_up;
+		goto out_put;
 
 	memcpy(addr->name, sunaddr, addr_len);
 	addr->len = addr_len;
@@ -1088,11 +1088,11 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 
 out_unlock:
 	spin_unlock(&unix_table_lock);
-out_up:
-	mutex_unlock(&u->bindlock);
 out_put:
 	if (err)
 		path_put(&path);
+out_up:
+	mutex_unlock(&u->bindlock);
 out:
 	return err;
 }
-- 
2.16.4

Re: [PATCH v3] net/af_unix: don't create a path for a binded socket

[Jakub Kicinski]

On Tue,  1 Dec 2020 12:33:06 +0300 Denis Kirjanov wrote:
> 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@SLES15-SP2:~> ./test
> First bind()
> Second bind()
> bind() failed
> : Invalid argument
> 
> kda@SLES15-SP2:~> ls -la /tmp/.first_bind
> .first_bind         .first_bind_failed
> 
> Signed-off-by: Denis Kirjanov <kda@linux-powerpc.org>

Is the deadlock fixed by the patch Michal pointed out no longer present?

Re: [PATCH v3] net/af_unix: don't create a path for a binded socket

[Denis Kirjanov]

On 12/1/20, Jakub Kicinski <kuba@kernel.org> wrote:
> On Tue,  1 Dec 2020 12:33:06 +0300 Denis Kirjanov wrote:
>> 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@SLES15-SP2:~> ./test
>> First bind()
>> Second bind()
>> bind() failed
>> : Invalid argument
>>
>> kda@SLES15-SP2:~> ls -la /tmp/.first_bind
>> .first_bind         .first_bind_failed
>>
>> Signed-off-by: Denis Kirjanov <kda@linux-powerpc.org>
>
> Is the deadlock fixed by the patch Michal pointed out no longer present?
The thing that I'm not satisfied is that we're holding bindlock during
unix_mknod().
I'll send a next version

>