Patch "af_unix: fix hard linked sockets on overlay" has been added to the 4.6-stable tree

This is a note to let you know that I've just added the patch titled

af_unix: fix hard linked sockets on overlay

to the 4.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
af_unix-fix-hard-linked-sockets-on-overlay.patch
and it can be found in the queue-4.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Miklos Szeredi <[email protected]>
Date: Fri, 20 May 2016 22:13:45 +0200
Subject: af_unix: fix hard linked sockets on overlay

From: Miklos Szeredi <[email protected]>

commit eb0a4a47ae89aaa0674ab3180de6a162f3be2ddf upstream.

Overlayfs uses separate inodes even in the case of hard links on the underlying filesystems. This is a problem for AF_UNIX socket implementation which indexes sockets based on the inode. This resulted in hard linked sockets not working.

The fix is to use the real, underlying inode.

Test case follows:

-- ovl-sock-test.c --
#include <unistd.h>
#include <err.h>
#include <sys/socket.h>
#include <sys/un.h>

#define SOCK "test-sock"
#define SOCK2 "test-sock2"

int main(void)

{
	int fd, fd2;
	struct sockaddr_un addr = {
		.sun_family = AF_UNIX,
		.sun_path = SOCK,
	};
	struct sockaddr_un addr2 = {
		.sun_family = AF_UNIX,
		.sun_path = SOCK2,
	};

	unlink(SOCK);
	unlink(SOCK2);
	if ((fd = socket(AF_UNIX, SOCK_STREAM, 0)) == -1)
		err(1, "socket");
	if (bind(fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
		err(1, "bind");
	if (listen(fd, 0) == -1)
		err(1, "listen");
	if (link(SOCK, SOCK2) == -1)
		err(1, "link");
	if ((fd2 = socket(AF_UNIX, SOCK_STREAM, 0)) == -1)
		err(1, "socket");
	if (connect(fd2, (struct sockaddr *) &addr2, sizeof(addr2)) == -1)
		err (1, "connect");
	return 0;
}

----

---
 net/unix/af_unix.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

@@ -315,7 +315,7 @@ static struct sock *unix_find_socket_byi
 		    &unix_socket_table[i->i_ino & (UNIX_HASH_SIZE - 1)]) {
 		struct dentry *dentry = unix_sk(s)->path.dentry;
 
-		if (dentry && d_backing_inode(dentry) == i) {
+		if (dentry && d_real_inode(dentry) == i) {
 			sock_hold(s);
 			goto found;
 		}

@@ -911,7 +911,7 @@ static struct sock *unix_find_other(stru
 		err = kern_path(sunname->sun_path, LOOKUP_FOLLOW, &path);
 		if (err)
 			goto fail;
-		inode = d_backing_inode(path.dentry);
+		inode = d_real_inode(path.dentry);
 		err = inode_permission(inode, MAY_WRITE);
 		if (err)
 			goto put_fail;

@@ -1048,7 +1048,7 @@ static int unix_bind(struct socket *sock
 			goto out_up;
 		}
 		addr->hash = UNIX_HASH_SIZE;
-		hash = d_backing_inode(dentry)->i_ino & (UNIX_HASH_SIZE - 1);
+		hash = d_real_inode(dentry)->i_ino & (UNIX_HASH_SIZE - 1);
 		spin_lock(&unix_table_lock);
 		u->path = u_path;
 		list = &unix_socket_table[hash];

Patches currently in stable-queue which might be from [email protected] are

queue-4.6/vfs-add-d_real_inode-helper.patch queue-4.6/af_unix-fix-hard-linked-sockets-on-overlay.patch