socket: close race condition between sock_close() and sockfs_setattr() (CVE-2018-12232)

debian/changelog

@@ -16,6 +16,8 @@ linux (4.17.2-1) UNRELEASED; urgency=medium
     (CVE-2018-10840)
   * ext4: do not allow external inodes for inline data (CVE-2018-11412)
   * ext4: bubble errors from ext4_find_inline_data_nolock() up to ext4_iget()
+  * socket: close race condition between sock_close() and sockfs_setattr()
+    (CVE-2018-12232)
 
   [ Romain Perier ]
   * [x86] Enable DCN 1.0 Raven family (Closes #901349)

debian/patches/bugfix/all/socket-close-race-condition-between-sock_close-and-s.patch

@@ -0,0 +1,87 @@
+From: Cong Wang <xiyou.wangcong@gmail.com>
+Date: Thu, 7 Jun 2018 13:39:49 -0700
+Subject: socket: close race condition between sock_close() and
+ sockfs_setattr()
+Origin: https://git.kernel.org/linus/6d8c50dcb029872b298eea68cc6209c866fd3e14
+Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2018-12232
+
+fchownat() doesn't even hold refcnt of fd until it figures out
+fd is really needed (otherwise is ignored) and releases it after
+it resolves the path. This means sock_close() could race with
+sockfs_setattr(), which leads to a NULL pointer dereference
+since typically we set sock->sk to NULL in ->release().
+
+As pointed out by Al, this is unique to sockfs. So we can fix this
+in socket layer by acquiring inode_lock in sock_close() and
+checking against NULL in sockfs_setattr().
+
+sock_release() is called in many places, only the sock_close()
+path matters here. And fortunately, this should not affect normal
+sock_close() as it is only called when the last fd refcnt is gone.
+It only affects sock_close() with a parallel sockfs_setattr() in
+progress, which is not common.
+
+Fixes: 86741ec25462 ("net: core: Add a UID field to struct sock.")
+Reported-by: shankarapailoor <shankarapailoor@gmail.com>
+Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
+Cc: Lorenzo Colitti <lorenzo@google.com>
+Cc: Al Viro <viro@zeniv.linux.org.uk>
+Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ net/socket.c | 18 +++++++++++++++---
+ 1 file changed, 15 insertions(+), 3 deletions(-)
+
+--- a/net/socket.c
++++ b/net/socket.c
+@@ -537,7 +537,10 @@ static int sockfs_setattr(struct dentry
+ 	if (!err && (iattr->ia_valid & ATTR_UID)) {
+ 		struct socket *sock = SOCKET_I(d_inode(dentry));
+ 
+-		sock->sk->sk_uid = iattr->ia_uid;
++		if (sock->sk)
++			sock->sk->sk_uid = iattr->ia_uid;
++		else
++			err = -ENOENT;
+ 	}
+ 
+ 	return err;
+@@ -586,12 +589,16 @@ EXPORT_SYMBOL(sock_alloc);
+  *	an inode not a file.
+  */
+ 
+-void sock_release(struct socket *sock)
++static void __sock_release(struct socket *sock, struct inode *inode)
+ {
+ 	if (sock->ops) {
+ 		struct module *owner = sock->ops->owner;
+ 
++		if (inode)
++			inode_lock(inode);
+ 		sock->ops->release(sock);
++		if (inode)
++			inode_unlock(inode);
+ 		sock->ops = NULL;
+ 		module_put(owner);
+ 	}
+@@ -605,6 +612,11 @@ void sock_release(struct socket *sock)
+ 	}
+ 	sock->file = NULL;
+ }
++
++void sock_release(struct socket *sock)
++{
++	__sock_release(sock, NULL);
++}
+ EXPORT_SYMBOL(sock_release);
+ 
+ void __sock_tx_timestamp(__u16 tsflags, __u8 *tx_flags)
+@@ -1146,7 +1158,7 @@ static int sock_mmap(struct file *file,
+ 
+ static int sock_close(struct inode *inode, struct file *filp)
+ {
+-	sock_release(SOCKET_I(inode));
++	__sock_release(SOCKET_I(inode), inode);
+ 	return 0;
+ }
+ 

debian/patches/series

@@ -129,6 +129,7 @@ bugfix/all/vhost-fix-info-leak-due-to-uninitialized-memory.patch
 bugfix/all/ext4-correctly-handle-a-zero-length-xattr-with-a-non.patch
 bugfix/all/ext4-do-not-allow-external-inodes-for-inline-data.patch
 bugfix/all/ext4-bubble-errors-from-ext4_find_inline_data_nolock.patch
+bugfix/all/socket-close-race-condition-between-sock_close-and-s.patch
 
 # Fix exported symbol versions
 bugfix/all/module-disable-matching-missing-version-crc.patch