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

From: Stanislav Kinsbursky <[email-masked]>
Date: Fri, 10 Aug 2012 22:43:59 +0400

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 <[email-masked]>
>> ---
>>   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;
>>
>> --
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