[PATCH 4.6 101/203] af_unix: fix hard linked sockets on overlay

Greg Kroah-Hartman
2016-07-25T21:33:33Z

From: Miklos Szeredi <mszeredi@redhat.com>

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;
}
----

Reported-by: Alexander Morozov <alexandr.morozov@docker.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -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];