[PATCH 0/2] more overlayfs hard link fixes

[PATCH 0/2] more overlayfs hard link fixes

[Miklos Szeredi]

Hi Al,

Git tree (with previously posted vfs patches as well) is available here:

  git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git d_real

Please pull.

Thanks,
Miklos

---
Miklos Szeredi (5):
      vfs: add d_real_inode() helper
      af_unix: fix hard linked sockets on overlay
      vfs: merge .d_select_inode() into .d_real()
      vfs: document ->d_real()
      vfs: clean up documentation

---
 Documentation/filesystems/Locking |  4 ++--
 Documentation/filesystems/vfs.txt | 39 +++++++++++++++++++++++++--------------
 fs/dcache.c                       |  3 ---
 fs/namei.c                        |  2 +-
 fs/open.c                         | 17 +++++++++++++----
 fs/overlayfs/inode.c              | 31 ++++++++++---------------------
 fs/overlayfs/overlayfs.h          |  2 +-
 fs/overlayfs/super.c              | 17 +++++++++++++----
 include/linux/dcache.h            | 35 ++++++++++++++++++++---------------
 include/linux/fs.h                |  2 +-
 net/unix/af_unix.c                |  6 +++---
 11 files changed, 89 insertions(+), 69 deletions(-)

[PATCH 1/2] vfs: add d_real_inode() helper

[Miklos Szeredi]

Needed by the following fix.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org>
---
 include/linux/dcache.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 7e9422cb5989..ad5d582f9b14 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -576,5 +576,17 @@ static inline struct inode *vfs_select_inode(struct dentry *dentry,
 	return inode;
 }
 
+/**
+ * d_real_inode - Return the real inode
+ * @dentry: The dentry to query
+ *
+ * If dentry is on an union/overlay, then return the underlying, real inode.
+ * Otherwise return d_inode().
+ */
+static inline struct inode *d_real_inode(struct dentry *dentry)
+{
+	return d_backing_inode(d_real(dentry));
+}
+
 
 #endif	/* __LINUX_DCACHE_H */
-- 
2.5.5

[PATCH 2/2] af_unix: fix hard linked sockets on overlay

[Miklos Szeredi]

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>
Cc: <stable@vger.kernel.org>
---
 net/unix/af_unix.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 8269da73e9e5..7748199b3568 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -315,7 +315,7 @@ static struct sock *unix_find_socket_byinode(struct inode *i)
 		    &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(struct net *net,
 		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, struct sockaddr *uaddr, int addr_len)
 			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];
-- 
2.5.5