[RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[Stanislav Kinsbursky]

Today, there is a problem in connecting of local SUNRPC thansports. These
transports uses UNIX sockets and connection itself is done by rpciod
workqueue.
But UNIX sockets lookup is done in context of process file system root. I.e.
all local thunsports are connecting in rpciod context.
This works nice until we will try to mount NFS from process with other root -
for example in container. This container can have it's own (nested) root and
rcpbind process, listening on it's own unix sockets. But NFS mount attempt in
this container will register new service (Lockd for example) in global rpcbind
- not containers's one.

This patch set introduces kernel connect helper for UNIX stream sockets and
modifies unix_find_other() to be able to search from specified root.
It also replaces generic socket connect call for local transports by new
helper in SUNRPC layer.

The following series implements...

---

Stanislav Kinsbursky (2):
      unix sockets: add ability for search for peer from passed root
      SUNRPC: connect local transports with unix_stream_connect_root() helper


 include/net/af_unix.h |    2 ++
 net/sunrpc/xprtsock.c |   28 +++++++++++++++++++++++++---
 net/unix/af_unix.c    |   25 ++++++++++++++++++-------
 3 files changed, 45 insertions(+), 10 deletions(-)

[RFC PATCH 1/2] unix sockets: add ability for search for peer from passed root

[Stanislav Kinsbursky]

This helper is used stream sockets yet.
All is simple: if non-NULL struct path was passed to unix_find_other(), then
vfs_path_lookup() is called instead of kern_path().

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
---
 include/net/af_unix.h |    2 ++
 net/unix/af_unix.c    |   25 ++++++++++++++++++-------
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/include/net/af_unix.h b/include/net/af_unix.h
index 2ee33da..559467e 100644
--- a/include/net/af_unix.h
+++ b/include/net/af_unix.h
@@ -67,6 +67,8 @@ struct unix_sock {
 
 long unix_inq_len(struct sock *sk);
 long unix_outq_len(struct sock *sk);
+int unix_stream_connect_root(struct path *root, struct socket *sock,
+			     struct sockaddr *uaddr, int addr_len, int flags);
 
 #ifdef CONFIG_SYSCTL
 extern int unix_sysctl_register(struct net *net);
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 641f2e4..a790ebc 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -759,7 +759,7 @@ out:	mutex_unlock(&u->readlock);
 	return err;
 }
 
-static struct sock *unix_find_other(struct net *net,
+static struct sock *unix_find_other(struct net *net, struct path *root,
 				    struct sockaddr_un *sunname, int len,
 				    int type, unsigned int hash, int *error)
 {
@@ -769,7 +769,11 @@ static struct sock *unix_find_other(struct net *net,
 
 	if (sunname->sun_path[0]) {
 		struct inode *inode;
-		err = kern_path(sunname->sun_path, LOOKUP_FOLLOW, &path);
+
+		if (root)
+			err = vfs_path_lookup(root->dentry, root->mnt, sunname->sun_path, LOOKUP_FOLLOW, &path);
+		else
+			err = kern_path(sunname->sun_path, LOOKUP_FOLLOW, &path);
 		if (err)
 			goto fail;
 		inode = path.dentry->d_inode;
@@ -979,7 +983,7 @@ static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr,
 			goto out;
 
 restart:
-		other = unix_find_other(net, sunaddr, alen, sock->type, hash, &err);
+		other = unix_find_other(net, NULL, sunaddr, alen, sock->type, hash, &err);
 		if (!other)
 			goto out;
 
@@ -1053,8 +1057,8 @@ static long unix_wait_for_peer(struct sock *other, long timeo)
 	return timeo;
 }
 
-static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
-			       int addr_len, int flags)
+int unix_stream_connect_root(struct path *root, struct socket *sock,
+			     struct sockaddr *uaddr, int addr_len, int flags)
 {
 	struct sockaddr_un *sunaddr = (struct sockaddr_un *)uaddr;
 	struct sock *sk = sock->sk;
@@ -1098,7 +1102,7 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 
 restart:
 	/*  Find listening sock. */
-	other = unix_find_other(net, sunaddr, addr_len, sk->sk_type, hash, &err);
+	other = unix_find_other(net, root, sunaddr, addr_len, sk->sk_type, hash, &err);
 	if (!other)
 		goto out;
 
@@ -1227,6 +1231,13 @@ out:
 		sock_put(other);
 	return err;
 }
+EXPORT_SYMBOL_GPL(unix_stream_connect_root);
+
+static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
+				    int addr_len, int flags)
+{
+	return unix_stream_connect_root(NULL, sock, uaddr, addr_len, flags);
+}
 
 static int unix_socketpair(struct socket *socka, struct socket *sockb)
 {
@@ -1508,7 +1519,7 @@ restart:
 		if (sunaddr == NULL)
 			goto out_free;
 
-		other = unix_find_other(net, sunaddr, namelen, sk->sk_type,
+		other = unix_find_other(net, NULL, sunaddr, namelen, sk->sk_type,
 					hash, &err);
 		if (other == NULL)
 			goto out_free;

Re: [RFC PATCH 1/2] unix sockets: add ability for search for peer from passed root

[J. Bruce Fields]

On Fri, Aug 10, 2012 at 04:57:30PM +0400, Stanislav Kinsbursky wrote:
> This helper is used stream sockets yet.
> All is simple: if non-NULL struct path was passed to unix_find_other(), then
> vfs_path_lookup() is called instead of kern_path().

I'm having some trouble parsing the changelog.  Maybe something like?:

	unix sockets: add ability to look up using passed-in root

	Export a unix_stream_connect_root() helper that allows a caller
	to optionally pass in a root path, in which case the lookup will
	be done relative to the given path instead of the current
	working directory.

I guess this is a question for the networking people, but: will it cause
problems to have sunrpc calling directly into the unix socket code?

(And if so, what would be the alternative: define some variant of
sockaddr_un that includes the root path?  Something better?)

--b.

> 
> Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
> ---
>  include/net/af_unix.h |    2 ++
>  net/unix/af_unix.c    |   25 ++++++++++++++++++-------
>  2 files changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/include/net/af_unix.h b/include/net/af_unix.h
> index 2ee33da..559467e 100644
> --- a/include/net/af_unix.h
> +++ b/include/net/af_unix.h
> @@ -67,6 +67,8 @@ struct unix_sock {
>  
>  long unix_inq_len(struct sock *sk);
>  long unix_outq_len(struct sock *sk);
> +int unix_stream_connect_root(struct path *root, struct socket *sock,
> +			     struct sockaddr *uaddr, int addr_len, int flags);
>  
>  #ifdef CONFIG_SYSCTL
>  extern int unix_sysctl_register(struct net *net);
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 641f2e4..a790ebc 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -759,7 +759,7 @@ out:	mutex_unlock(&u->readlock);
>  	return err;
>  }
>  
> -static struct sock *unix_find_other(struct net *net,
> +static struct sock *unix_find_other(struct net *net, struct path *root,
>  				    struct sockaddr_un *sunname, int len,
>  				    int type, unsigned int hash, int *error)
>  {
> @@ -769,7 +769,11 @@ static struct sock *unix_find_other(struct net *net,
>  
>  	if (sunname->sun_path[0]) {
>  		struct inode *inode;
> -		err = kern_path(sunname->sun_path, LOOKUP_FOLLOW, &path);
> +
> +		if (root)
> +			err = vfs_path_lookup(root->dentry, root->mnt, sunname->sun_path, LOOKUP_FOLLOW, &path);
> +		else
> +			err = kern_path(sunname->sun_path, LOOKUP_FOLLOW, &path);
>  		if (err)
>  			goto fail;
>  		inode = path.dentry->d_inode;
> @@ -979,7 +983,7 @@ static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr,
>  			goto out;
>  
>  restart:
> -		other = unix_find_other(net, sunaddr, alen, sock->type, hash, &err);
> +		other = unix_find_other(net, NULL, sunaddr, alen, sock->type, hash, &err);
>  		if (!other)
>  			goto out;
>  
> @@ -1053,8 +1057,8 @@ static long unix_wait_for_peer(struct sock *other, long timeo)
>  	return timeo;
>  }
>  
> -static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
> -			       int addr_len, int flags)
> +int unix_stream_connect_root(struct path *root, struct socket *sock,
> +			     struct sockaddr *uaddr, int addr_len, int flags)
>  {
>  	struct sockaddr_un *sunaddr = (struct sockaddr_un *)uaddr;
>  	struct sock *sk = sock->sk;
> @@ -1098,7 +1102,7 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
>  
>  restart:
>  	/*  Find listening sock. */
> -	other = unix_find_other(net, sunaddr, addr_len, sk->sk_type, hash, &err);
> +	other = unix_find_other(net, root, sunaddr, addr_len, sk->sk_type, hash, &err);
>  	if (!other)
>  		goto out;
>  
> @@ -1227,6 +1231,13 @@ out:
>  		sock_put(other);
>  	return err;
>  }
> +EXPORT_SYMBOL_GPL(unix_stream_connect_root);
> +
> +static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
> +				    int addr_len, int flags)
> +{
> +	return unix_stream_connect_root(NULL, sock, uaddr, addr_len, flags);
> +}
>  
>  static int unix_socketpair(struct socket *socka, struct socket *sockb)
>  {
> @@ -1508,7 +1519,7 @@ restart:
>  		if (sunaddr == NULL)
>  			goto out_free;
>  
> -		other = unix_find_other(net, sunaddr, namelen, sk->sk_type,
> +		other = unix_find_other(net, NULL, sunaddr, namelen, sk->sk_type,
>  					hash, &err);
>  		if (other == NULL)
>  			goto out_free;
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [RFC PATCH 1/2] unix sockets: add ability for search for peer from passed root

[Stanislav Kinsbursky]

10.08.2012 22:10, J. Bruce Fields пишет:
> On Fri, Aug 10, 2012 at 04:57:30PM +0400, Stanislav Kinsbursky wrote:
>> This helper is used stream sockets yet.
>> All is simple: if non-NULL struct path was passed to unix_find_other(), then
>> vfs_path_lookup() is called instead of kern_path().
> I'm having some trouble parsing the changelog.  Maybe something like?:
>
> 	unix sockets: add ability to look up using passed-in root
>
> 	Export a unix_stream_connect_root() helper that allows a caller
> 	to optionally pass in a root path, in which case the lookup will
> 	be done relative to the given path instead of the current
> 	working directory.

Yep, your variant is much better. Thanks.

>
> I guess this is a question for the networking people, but: will it cause
> problems to have sunrpc calling directly into the unix socket code?
>
> (And if so, what would be the alternative: define some variant of
> sockaddr_un that includes the root path?  Something better?)

That was my first idea. But there are problems with this solution (add 
root path to sockaddr_un) :
1) sockaddr_un size will change. I don't know, how this will affect 
user-space. Of course, we can introduce something like:

struct sockaddr_un_kern {
struct sockaddr_un un;
struct path *path;
}

But even in this case we need to color this structure somehow (for 
example, set path to NULL for simple connect or bind call) . And to add 
this color, we have to separate sys_connect () from our 
sock->ops->connect() call. And I don't really know how to do it since we 
don't have any info about socket type in sys_connect () in hands. I.e. 
we have it, but then we have to add some specific UNIX socket logic to 
completely generic sys_connect () and sys_bind () .

> --b.
>
>> Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
>> ---
>>   include/net/af_unix.h |    2 ++
>>   net/unix/af_unix.c    |   25 ++++++++++++++++++-------
>>   2 files changed, 20 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/net/af_unix.h b/include/net/af_unix.h
>> index 2ee33da..559467e 100644
>> --- a/include/net/af_unix.h
>> +++ b/include/net/af_unix.h
>> @@ -67,6 +67,8 @@ struct unix_sock {
>>   
>>   long unix_inq_len(struct sock *sk);
>>   long unix_outq_len(struct sock *sk);
>> +int unix_stream_connect_root(struct path *root, struct socket *sock,
>> +			     struct sockaddr *uaddr, int addr_len, int flags);
>>   
>>   #ifdef CONFIG_SYSCTL
>>   extern int unix_sysctl_register(struct net *net);
>> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
>> index 641f2e4..a790ebc 100644
>> --- a/net/unix/af_unix.c
>> +++ b/net/unix/af_unix.c
>> @@ -759,7 +759,7 @@ out:	mutex_unlock(&u->readlock);
>>   	return err;
>>   }
>>   
>> -static struct sock *unix_find_other(struct net *net,
>> +static struct sock *unix_find_other(struct net *net, struct path *root,
>>   				    struct sockaddr_un *sunname, int len,
>>   				    int type, unsigned int hash, int *error)
>>   {
>> @@ -769,7 +769,11 @@ static struct sock *unix_find_other(struct net *net,
>>   
>>   	if (sunname->sun_path[0]) {
>>   		struct inode *inode;
>> -		err = kern_path(sunname->sun_path, LOOKUP_FOLLOW, &path);
>> +
>> +		if (root)
>> +			err = vfs_path_lookup(root->dentry, root->mnt, sunname->sun_path, LOOKUP_FOLLOW, &path);
>> +		else
>> +			err = kern_path(sunname->sun_path, LOOKUP_FOLLOW, &path);
>>   		if (err)
>>   			goto fail;
>>   		inode = path.dentry->d_inode;
>> @@ -979,7 +983,7 @@ static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr,
>>   			goto out;
>>   
>>   restart:
>> -		other = unix_find_other(net, sunaddr, alen, sock->type, hash, &err);
>> +		other = unix_find_other(net, NULL, sunaddr, alen, sock->type, hash, &err);
>>   		if (!other)
>>   			goto out;
>>   
>> @@ -1053,8 +1057,8 @@ static long unix_wait_for_peer(struct sock *other, long timeo)
>>   	return timeo;
>>   }
>>   
>> -static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
>> -			       int addr_len, int flags)
>> +int unix_stream_connect_root(struct path *root, struct socket *sock,
>> +			     struct sockaddr *uaddr, int addr_len, int flags)
>>   {
>>   	struct sockaddr_un *sunaddr = (struct sockaddr_un *)uaddr;
>>   	struct sock *sk = sock->sk;
>> @@ -1098,7 +1102,7 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
>>   
>>   restart:
>>   	/*  Find listening sock. */
>> -	other = unix_find_other(net, sunaddr, addr_len, sk->sk_type, hash, &err);
>> +	other = unix_find_other(net, root, sunaddr, addr_len, sk->sk_type, hash, &err);
>>   	if (!other)
>>   		goto out;
>>   
>> @@ -1227,6 +1231,13 @@ out:
>>   		sock_put(other);
>>   	return err;
>>   }
>> +EXPORT_SYMBOL_GPL(unix_stream_connect_root);
>> +
>> +static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
>> +				    int addr_len, int flags)
>> +{
>> +	return unix_stream_connect_root(NULL, sock, uaddr, addr_len, flags);
>> +}
>>   
>>   static int unix_socketpair(struct socket *socka, struct socket *sockb)
>>   {
>> @@ -1508,7 +1519,7 @@ restart:
>>   		if (sunaddr == NULL)
>>   			goto out_free;
>>   
>> -		other = unix_find_other(net, sunaddr, namelen, sk->sk_type,
>> +		other = unix_find_other(net, NULL, sunaddr, namelen, sk->sk_type,
>>   					hash, &err);
>>   		if (other == NULL)
>>   			goto out_free;
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html

[RFC PATCH 2/2] SUNRPC: connect local transports with unix_stream_connect_root() helper

[Stanislav Kinsbursky]

Today, there is a problem in connecting of local SUNRPC thansports. These
transports uses UNIX sockets and connection itself is done by rpciod
workqueue.
But UNIX sockets lookup is done in context of process file system root. I.e.
all local thunsports are connecting in rpciod context.
This works nice until we will try to mount NFS from process with other root -
for example in container. This container can have it's own (nested) root and
rcpbind process, listening on it's own unix sockets. But NFS mount attempt in
this container will register new service (Lockd for example) in global rpcbind
- not containers's one.
This patch solves the problem by using special helper
unix_stream_connect_root(), which lookup socket file starting from passed
root.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
---
 net/sunrpc/xprtsock.c |   28 +++++++++++++++++++++++++---
 1 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 890b03f..01a6f2a 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -37,6 +37,7 @@
 #include <linux/sunrpc/svcsock.h>
 #include <linux/sunrpc/xprtsock.h>
 #include <linux/file.h>
+#include <linux/fs_struct.h>
 #ifdef CONFIG_SUNRPC_BACKCHANNEL
 #include <linux/sunrpc/bc_xprt.h>
 #endif
@@ -45,6 +46,7 @@
 #include <net/checksum.h>
 #include <net/udp.h>
 #include <net/tcp.h>
+#include <net/af_unix.h>
 
 #include "sunrpc.h"
 
@@ -255,6 +257,11 @@ struct sock_xprt {
 	void			(*old_state_change)(struct sock *);
 	void			(*old_write_space)(struct sock *);
 	void			(*old_error_report)(struct sock *);
+
+	/*
+	 * Saved transport creator root. Required for local transports only.
+	 */
+	struct path		root;
 };
 
 /*
@@ -1873,7 +1880,8 @@ static int xs_local_finish_connecting(struct rpc_xprt *xprt,
 	/* Tell the socket layer to start connecting... */
 	xprt->stat.connect_count++;
 	xprt->stat.connect_start = jiffies;
-	return kernel_connect(sock, xs_addr(xprt), xprt->addrlen, 0);
+	return unix_stream_connect_root(&transport->root, sock, xs_addr(xprt),
+					xprt->addrlen, 0);
 }
 
 /**
@@ -2213,6 +2221,18 @@ static void xs_connect(struct rpc_task *task)
 	}
 }
 
+static void xs_local_destroy(struct rpc_xprt *xprt)
+{
+	struct sock_xprt *transport = container_of(xprt, struct sock_xprt, xprt);
+	struct path root = transport->root;
+
+	dprintk("RPC:       xs_local_destroy xprt %p\n", xprt);
+
+	xs_destroy(xprt);
+
+	path_put(&root);
+}
+
 /**
  * xs_local_print_stats - display AF_LOCAL socket-specifc stats
  * @xprt: rpc_xprt struct containing statistics
@@ -2431,7 +2451,7 @@ static struct rpc_xprt_ops xs_local_ops = {
 	.send_request		= xs_local_send_request,
 	.set_retrans_timeout	= xprt_set_retrans_timeout_def,
 	.close			= xs_close,
-	.destroy		= xs_destroy,
+	.destroy		= xs_local_destroy,
 	.print_stats		= xs_local_print_stats,
 };
 
@@ -2607,8 +2627,10 @@ static struct rpc_xprt *xs_setup_local(struct xprt_create *args)
 	dprintk("RPC:       set up xprt to %s via AF_LOCAL\n",
 			xprt->address_strings[RPC_DISPLAY_ADDR]);
 
-	if (try_module_get(THIS_MODULE))
+	if (try_module_get(THIS_MODULE)) {
+		get_fs_root(current->fs, &transport->root);
 		return xprt;
+	}
 	ret = ERR_PTR(-EINVAL);
 out_err:
 	xprt_free(xprt);

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[H. Peter Anvin]

On 08/10/2012 05:57 AM, Stanislav Kinsbursky wrote:
> Today, there is a problem in connecting of local SUNRPC thansports. These
> transports uses UNIX sockets and connection itself is done by rpciod
> workqueue.
> But UNIX sockets lookup is done in context of process file system root. I.e.
> all local thunsports are connecting in rpciod context.
> This works nice until we will try to mount NFS from process with other root -
> for example in container. This container can have it's own (nested) root and
> rcpbind process, listening on it's own unix sockets. But NFS mount attempt in
> this container will register new service (Lockd for example) in global rpcbind
> - not containers's one.
> 
> This patch set introduces kernel connect helper for UNIX stream sockets and
> modifies unix_find_other() to be able to search from specified root.
> It also replaces generic socket connect call for local transports by new
> helper in SUNRPC layer.
> 
> The following series implements...

On that whole subject...

Do we need a Unix domain socket equivalent to openat()?

	-hpa

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[Alan Cox]

> On that whole subject...
> 
> Do we need a Unix domain socket equivalent to openat()?

I don't think so. The name is just a file system indexing trick, it's not
really the socket proper. It's little more than "ascii string with
permissions attached" - indeed we also support an abstract name space
which for a lot of uses is actually more convenient.

AF_UNIX between roots raises some interesting semantic questions when you
begin passing file descriptors down them as well.

Alan

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[H. Peter Anvin]

On 08/10/2012 11:26 AM, Alan Cox wrote:
>> On that whole subject...
>>
>> Do we need a Unix domain socket equivalent to openat()?
> 
> I don't think so. The name is just a file system indexing trick, it's not
> really the socket proper. It's little more than "ascii string with
> permissions attached" - indeed we also support an abstract name space
> which for a lot of uses is actually more convenient.
> 

I don't really understand why Unix domain sockets is different than any
other pathname users in this sense.  (Actually, I have never understood
why open() on a Unix domain socket doesn't give the equivalent of a
socket() + connect() -- it would make logical sense and would provide
additional functionality).

It would be different if the Unix domain sockets simply required an
absolute pathname (it is not just about the root, it is also about the
cwd, which is where the -at() functions come into play), but that is not
the case.

The abstract namespace is irrelevant for this, obviously.

> AF_UNIX between roots raises some interesting semantic questions when
> you begin passing file descriptors down them as well.

Why is that?  A file descriptor carries all that information with it...

	-hpa

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[Alan Cox]

> > AF_UNIX between roots raises some interesting semantic questions when
> > you begin passing file descriptors down them as well.
> 
> Why is that?  A file descriptor carries all that information with it...

Things like fchdir(). It's not a machine breaking problem but for
containers as opposed to chroot we need to be clear what the expected
isolation sematics are.

Agreed on open() for sockets.. the lack of open is a Berklix derived
pecularity of the interface. It would equally be useful to be able to
open "/dev/socket/ipv4/1.2.3.4/1135" and the like for scripts and stuff

That needs VFS changes however so you can pass the remainder of a path to
a device node. It also lets you do a lot of other sane stuff like

	open /dev/ttyS0/9600/8n1

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[H. Peter Anvin]

On 08/10/2012 11:40 AM, Alan Cox wrote:
> 
> Agreed on open() for sockets.. the lack of open is a Berklix derived
> pecularity of the interface. It would equally be useful to be able to
> open "/dev/socket/ipv4/1.2.3.4/1135" and the like for scripts and stuff
> 
> That needs VFS changes however so you can pass the remainder of a path to
> a device node. It also lets you do a lot of other sane stuff like
> 
> 	open /dev/ttyS0/9600/8n1
> 

Well, supporting device node subpaths would be nice, but I don't think
that that is a requirement either for being able to open() a socket (as
a Linux extension) nor for supporting something like your above
/dev/socket/... since that could be done with a filesystem rather than
just a device node.

	-hpa

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[J. Bruce Fields]

On Fri, Aug 10, 2012 at 07:26:28PM +0100, Alan Cox wrote:
> > On that whole subject...
> > 
> > Do we need a Unix domain socket equivalent to openat()?
> 
> I don't think so. The name is just a file system indexing trick, it's not
> really the socket proper. It's little more than "ascii string with
> permissions attached"

That's overstating the case.  As I understand it the address is resolved
by a pathname lookup like any other--it can follow symlinks, is relative
to the current working directory and filesystem namespace, etc.  So a
unix-domain socket equivalent to openat() would at least be
well-defined--whether it's needed or not, I don't know.

--b.

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[Alan Cox]

On Fri, 10 Aug 2012 15:11:50 -0400
"J. Bruce Fields" <bfields@fieldses.org> wrote:

> On Fri, Aug 10, 2012 at 07:26:28PM +0100, Alan Cox wrote:
> > > On that whole subject...
> > > 
> > > Do we need a Unix domain socket equivalent to openat()?
> > 
> > I don't think so. The name is just a file system indexing trick, it's not
> > really the socket proper. It's little more than "ascii string with
> > permissions attached"
> 
> That's overstating the case.  As I understand it the address is resolved
> by a pathname lookup like any other--it can follow symlinks, is relative
> to the current working directory and filesystem namespace, etc. 

Explicitly for Linux yes - this is not generally true of the AF_UNIX
socket domain and even the permissions aspect isn't guaranteed to be
supported on some BSD environments !

The name is however just a proxy for the socket itself. You don't even
get a device node in the usual sense or the same inode in the file system
space.

Alan

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[H. Peter Anvin]

On 08/10/2012 12:28 PM, Alan Cox wrote:
> Explicitly for Linux yes - this is not generally true of the AF_UNIX
> socket domain and even the permissions aspect isn't guaranteed to be
> supported on some BSD environments !

Yes, but let's worry about what the Linux behavior should be.

> The name is however just a proxy for the socket itself. You don't even
> get a device node in the usual sense or the same inode in the file system
> space.


No, but it is looked up the same way any other inode is (the difference
between FIFOs and sockets is that sockets have separate connections,
which is also why open() on sockets would be nice.)

However, there is a fundamental difference between AF_UNIX sockets and
open(), and that is how the pathname is delivered.  It thus would make
more sense to provide the openat()-like information in struct
sockaddr_un, but that may be very hard to do in a sensible way.  In that
sense it perhaps would be cleaner to be able to do an open[at]() on the
socket node with O_PATH (perhaps there should be an O_SOCKET option,
even?) and pass the resulting file descriptor to bind() or connect().

	-hpa

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[Pavel Emelyanov]

On 08/11/2012 03:09 AM, H. Peter Anvin wrote:
> On 08/10/2012 12:28 PM, Alan Cox wrote:
>> Explicitly for Linux yes - this is not generally true of the AF_UNIX
>> socket domain and even the permissions aspect isn't guaranteed to be
>> supported on some BSD environments !
> 
> Yes, but let's worry about what the Linux behavior should be.
> 
>> The name is however just a proxy for the socket itself. You don't even
>> get a device node in the usual sense or the same inode in the file system
>> space.
> 
> 
> No, but it is looked up the same way any other inode is (the difference
> between FIFOs and sockets is that sockets have separate connections,
> which is also why open() on sockets would be nice.)
> 
> However, there is a fundamental difference between AF_UNIX sockets and
> open(), and that is how the pathname is delivered.  It thus would make
> more sense to provide the openat()-like information in struct
> sockaddr_un, but that may be very hard to do in a sensible way.  In that
> sense it perhaps would be cleaner to be able to do an open[at]() on the
> socket node with O_PATH (perhaps there should be an O_SOCKET option,
> even?) and pass the resulting file descriptor to bind() or connect().

I vote for this (openat + O_WHATEVER on a unix socket) as well. It will 
help us in checkpoint-restore, making handling of overmounted/unlinked
sockets much cleaner.

> 	-hpa

Thanks,
Pavel

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[Stanislav Kinsbursky]

11.08.2012 10:23, Pavel Emelyanov пишет:
> On 08/11/2012 03:09 AM, H. Peter Anvin wrote:
>> On 08/10/2012 12:28 PM, Alan Cox wrote:
>>> Explicitly for Linux yes - this is not generally true of the AF_UNIX
>>> socket domain and even the permissions aspect isn't guaranteed to be
>>> supported on some BSD environments !
>> Yes, but let's worry about what the Linux behavior should be.
>>
>>> The name is however just a proxy for the socket itself. You don't even
>>> get a device node in the usual sense or the same inode in the file system
>>> space.
>>
>> No, but it is looked up the same way any other inode is (the difference
>> between FIFOs and sockets is that sockets have separate connections,
>> which is also why open() on sockets would be nice.)
>>
>> However, there is a fundamental difference between AF_UNIX sockets and
>> open(), and that is how the pathname is delivered.  It thus would make
>> more sense to provide the openat()-like information in struct
>> sockaddr_un, but that may be very hard to do in a sensible way.  In that
>> sense it perhaps would be cleaner to be able to do an open[at]() on the
>> socket node with O_PATH (perhaps there should be an O_SOCKET option,
>> even?) and pass the resulting file descriptor to bind() or connect().
> I vote for this (openat + O_WHATEVER on a unix socket) as well. It will
> help us in checkpoint-restore, making handling of overmounted/unlinked
> sockets much cleaner.

I have to notice, that it's not enough and doesn't solve the issue.
There should be some way how to connect/bind already existent unix 
socket (from kernel, at least), because socket can be created in user space.
And this way (sock operation or whatever) have to provide an ability to 
lookup UNIX socket starting from specified root to support containers.

>
>> 	-hpa
> Thanks,
> Pavel
>

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[J. Bruce Fields]

On Sat, Aug 11, 2012 at 03:15:24PM +0400, Stanislav Kinsbursky wrote:
> 11.08.2012 10:23, Pavel Emelyanov пишет:
> >On 08/11/2012 03:09 AM, H. Peter Anvin wrote:
> >>On 08/10/2012 12:28 PM, Alan Cox wrote:
> >>>Explicitly for Linux yes - this is not generally true of the AF_UNIX
> >>>socket domain and even the permissions aspect isn't guaranteed to be
> >>>supported on some BSD environments !
> >>Yes, but let's worry about what the Linux behavior should be.
> >>
> >>>The name is however just a proxy for the socket itself. You don't even
> >>>get a device node in the usual sense or the same inode in the file system
> >>>space.
> >>
> >>No, but it is looked up the same way any other inode is (the difference
> >>between FIFOs and sockets is that sockets have separate connections,
> >>which is also why open() on sockets would be nice.)
> >>
> >>However, there is a fundamental difference between AF_UNIX sockets and
> >>open(), and that is how the pathname is delivered.  It thus would make
> >>more sense to provide the openat()-like information in struct
> >>sockaddr_un, but that may be very hard to do in a sensible way.  In that
> >>sense it perhaps would be cleaner to be able to do an open[at]() on the
> >>socket node with O_PATH (perhaps there should be an O_SOCKET option,
> >>even?) and pass the resulting file descriptor to bind() or connect().
> >I vote for this (openat + O_WHATEVER on a unix socket) as well. It will
> >help us in checkpoint-restore, making handling of overmounted/unlinked
> >sockets much cleaner.
> 
> I have to notice, that it's not enough and doesn't solve the issue.
> There should be some way how to connect/bind already existent unix
> socket (from kernel, at least), because socket can be created in
> user space.
> And this way (sock operation or whatever) have to provide an ability
> to lookup UNIX socket starting from specified root to support
> containers.

I don't understand--the rpcbind sockets are created by the kernel.  What
am I missing?

--b.

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[Stanislav Kinsbursky]

13.08.2012 20:47, J. Bruce Fields пишет:
> On Sat, Aug 11, 2012 at 03:15:24PM +0400, Stanislav Kinsbursky wrote:
>> 11.08.2012 10:23, Pavel Emelyanov пишет:
>>> On 08/11/2012 03:09 AM, H. Peter Anvin wrote:
>>>> On 08/10/2012 12:28 PM, Alan Cox wrote:
>>>>> Explicitly for Linux yes - this is not generally true of the AF_UNIX
>>>>> socket domain and even the permissions aspect isn't guaranteed to be
>>>>> supported on some BSD environments !
>>>> Yes, but let's worry about what the Linux behavior should be.
>>>>
>>>>> The name is however just a proxy for the socket itself. You don't even
>>>>> get a device node in the usual sense or the same inode in the file system
>>>>> space.
>>>> No, but it is looked up the same way any other inode is (the difference
>>>> between FIFOs and sockets is that sockets have separate connections,
>>>> which is also why open() on sockets would be nice.)
>>>>
>>>> However, there is a fundamental difference between AF_UNIX sockets and
>>>> open(), and that is how the pathname is delivered.  It thus would make
>>>> more sense to provide the openat()-like information in struct
>>>> sockaddr_un, but that may be very hard to do in a sensible way.  In that
>>>> sense it perhaps would be cleaner to be able to do an open[at]() on the
>>>> socket node with O_PATH (perhaps there should be an O_SOCKET option,
>>>> even?) and pass the resulting file descriptor to bind() or connect().
>>> I vote for this (openat + O_WHATEVER on a unix socket) as well. It will
>>> help us in checkpoint-restore, making handling of overmounted/unlinked
>>> sockets much cleaner.
>> I have to notice, that it's not enough and doesn't solve the issue.
>> There should be some way how to connect/bind already existent unix
>> socket (from kernel, at least), because socket can be created in
>> user space.
>> And this way (sock operation or whatever) have to provide an ability
>> to lookup UNIX socket starting from specified root to support
>> containers.
> I don't understand--the rpcbind sockets are created by the kernel.  What
> am I missing?

Kernel preform connect to rpcbind socket (i.e. user-space binds it), 
doesn't it?

>
> --b.

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[J. Bruce Fields]

On Mon, Aug 13, 2012 at 09:39:53PM +0400, Stanislav Kinsbursky wrote:
> 13.08.2012 20:47, J. Bruce Fields пишет:
> >On Sat, Aug 11, 2012 at 03:15:24PM +0400, Stanislav Kinsbursky wrote:
> >>11.08.2012 10:23, Pavel Emelyanov пишет:
> >>>On 08/11/2012 03:09 AM, H. Peter Anvin wrote:
> >>>>On 08/10/2012 12:28 PM, Alan Cox wrote:
> >>>>>Explicitly for Linux yes - this is not generally true of the AF_UNIX
> >>>>>socket domain and even the permissions aspect isn't guaranteed to be
> >>>>>supported on some BSD environments !
> >>>>Yes, but let's worry about what the Linux behavior should be.
> >>>>
> >>>>>The name is however just a proxy for the socket itself. You don't even
> >>>>>get a device node in the usual sense or the same inode in the file system
> >>>>>space.
> >>>>No, but it is looked up the same way any other inode is (the difference
> >>>>between FIFOs and sockets is that sockets have separate connections,
> >>>>which is also why open() on sockets would be nice.)
> >>>>
> >>>>However, there is a fundamental difference between AF_UNIX sockets and
> >>>>open(), and that is how the pathname is delivered.  It thus would make
> >>>>more sense to provide the openat()-like information in struct
> >>>>sockaddr_un, but that may be very hard to do in a sensible way.  In that
> >>>>sense it perhaps would be cleaner to be able to do an open[at]() on the
> >>>>socket node with O_PATH (perhaps there should be an O_SOCKET option,
> >>>>even?) and pass the resulting file descriptor to bind() or connect().
> >>>I vote for this (openat + O_WHATEVER on a unix socket) as well. It will
> >>>help us in checkpoint-restore, making handling of overmounted/unlinked
> >>>sockets much cleaner.
> >>I have to notice, that it's not enough and doesn't solve the issue.
> >>There should be some way how to connect/bind already existent unix
> >>socket (from kernel, at least), because socket can be created in
> >>user space.
> >>And this way (sock operation or whatever) have to provide an ability
> >>to lookup UNIX socket starting from specified root to support
> >>containers.
> >I don't understand--the rpcbind sockets are created by the kernel.  What
> >am I missing?
> 
> Kernel preform connect to rpcbind socket (i.e. user-space binds it),
> doesn't it?

I'm confused, possibly because there are three "sockets" here: the
client-side socket that's connected, the server-side socket that's
bound, and the common object that exists in the filesystem namespace.

Userland creates the server-side socket and binds to it.  All of that is
done in the context of the rpcbind process, so is created in rpcbind's
namespace.  That should be OK, right?

The client side socket is created and connected in
xs_local_setup_socket().

Making sure they both end up with the same thing is a matter of making
sure they lookup the same path in the same namespace.  The difficult
part of that is the in-kernel client-side socket connect, where we don't
have the right process context any more.

We currently set that up with __sock_create followed by
kernel_connect.

The proposal seems to be to instead do an openat followed by a
kernel_connect, and pass the path in the openat instead of the connect.

(Though in the kernel we won't be able to call openat, so we'll end up
doing something like nfsd does (calling lookup_one_len() and
dentry_open() by hand).)

Have I got all that right?

I don't know if that's better just calling into the unix socket code at
connect time as your patch does.  Maybe the answer depends on whether
it's a priority to make this functionality available to userspace.

--b.

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[Stanislav Kinsbursky]

13.08.2012 22:24, J. Bruce Fields пишет:
> On Mon, Aug 13, 2012 at 09:39:53PM +0400, Stanislav Kinsbursky wrote:
>> 13.08.2012 20:47, J. Bruce Fields пишет:
>>> On Sat, Aug 11, 2012 at 03:15:24PM +0400, Stanislav Kinsbursky wrote:
>>>> 11.08.2012 10:23, Pavel Emelyanov пишет:
>>>>> On 08/11/2012 03:09 AM, H. Peter Anvin wrote:
>>>>>> On 08/10/2012 12:28 PM, Alan Cox wrote:
>>>>>>> Explicitly for Linux yes - this is not generally true of the
>>>>>>> AF_UNIX socket domain and even the permissions aspect isn't
>>>>>>> guaranteed to be supported on some BSD environments !
>>>>>> Yes, but let's worry about what the Linux behavior should be.
>>>>>>
>>>>>>> The name is however just a proxy for the socket itself. You
>>>>>>> don't even get a device node in the usual sense or the same inode
>>>>>>> in the file system space.
>>>>>> No, but it is looked up the same way any other inode is (the
>>>>>> difference between FIFOs and sockets is that sockets have separate
>>>>>> connections, which is also why open() on sockets would be nice.)
>>>>>>
>>>>>> However, there is a fundamental difference between AF_UNIX sockets
>>>>>> and open(), and that is how the pathname is delivered.  It thus
>>>>>> would make more sense to provide the openat()-like information in
>>>>>> struct sockaddr_un, but that may be very hard to do in a sensible
>>>>>> way.  In that sense it perhaps would be cleaner to be able to do
>>>>>> an open[at]() on the socket node with O_PATH (perhaps there should
>>>>>> be an O_SOCKET option, even?) and pass the resulting file
>>>>>> descriptor to bind() or connect().
>>>>> I vote for this (openat + O_WHATEVER on a unix socket) as well. It
>>>>> will help us in checkpoint-restore, making handling of
>>>>> overmounted/unlinked sockets much cleaner.
>>>> I have to notice, that it's not enough and doesn't solve the issue.
>>>> There should be some way how to connect/bind already existent unix
>>>> socket (from kernel, at least), because socket can be created in user
>>>> space. And this way (sock operation or whatever) have to provide an
>>>> ability to lookup UNIX socket starting from specified root to support
>>>> containers.
>>> I don't understand--the rpcbind sockets are created by the kernel.  What
>>>  am I missing?
>>
>> Kernel preform connect to rpcbind socket (i.e. user-space binds it),
>> doesn't it?
>
> I'm confused, possibly because there are three "sockets" here: the
> client-side socket that's connected, the server-side socket that's bound,
> and the common object that exists in the filesystem namespace.
>
> Userland creates the server-side socket and binds to it.  All of that is
> done in the context of the rpcbind process, so is created in rpcbind's
> namespace. That should be OK, right?
>
> The client side socket is created and connected in xs_local_setup_socket().
>
> Making sure they both end up with the same thing is a matter of making sure
> they lookup the same path in the same namespace.  The difficult part of that
> is the in-kernel client-side socket connect, where we don't have the right
> process context any more.
>

Looks like I'm missing something important.
Where are these UNIX in-kernel created and listening sockets (in code, I mean)?

-- 
Best regards,
Stanislav Kinsbursky

Re: [RFC PATCH 0/2] net: connect to UNIX sockets from specified root

[Stanislav Kinsbursky]

10.08.2012 22:15, H. Peter Anvin пишет:
> On 08/10/2012 05:57 AM, Stanislav Kinsbursky wrote:
>> Today, there is a problem in connecting of local SUNRPC thansports. These
>> transports uses UNIX sockets and connection itself is done by rpciod
>> workqueue.
>> But UNIX sockets lookup is done in context of process file system root. I.e.
>> all local thunsports are connecting in rpciod context.
>> This works nice until we will try to mount NFS from process with other root -
>> for example in container. This container can have it's own (nested) root and
>> rcpbind process, listening on it's own unix sockets. But NFS mount attempt in
>> this container will register new service (Lockd for example) in global rpcbind
>> - not containers's one.
>>
>> This patch set introduces kernel connect helper for UNIX stream sockets and
>> modifies unix_find_other() to be able to search from specified root.
>> It also replaces generic socket connect call for local transports by new
>> helper in SUNRPC layer.
>>
>> The following series implements...
> On that whole subject...
>
> Do we need a Unix domain socket equivalent to openat()?

It looks like sys_connectat () and sys_bindat () could be an organic 
part on openat () and friends family.
But currently I don't have any usage example for them in hands.  And the 
main problem here, that this syscalls can be used only for unix sockets.