net: socket: don't set sk_uid to garbage value in ->setattr()

->setattr() was recently implemented for socket files to sync the socket
inode's uid to the new 'sk_uid' member of struct sock.  It does this by
copying over the ia_uid member of struct iattr.  However, ia_uid is
actually only valid when ATTR_UID is set in ia_valid, indicating that
the uid is being changed, e.g. by chown.  Other metadata operations such
as chmod or utimes leave ia_uid uninitialized.  Therefore, sk_uid could
be set to a "garbage" value from the stack.

Fix this by only copying the uid over when ATTR_UID is set.

[cherry-pick of net e1a3a60a2ebe991605acb14cd58e39c0545e174e]

Bug: 16355602
Change-Id: I20e53848e54282b72a388ce12bfa88da5e3e9efe
Fixes: 86741ec25462 ("net: core: Add a UID field to struct sock.")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Tested-by: Lorenzo Colitti <lorenzo@google.com>
Acked-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/socket.c b/net/socket.c
index 66d984ac29917200ac65258a220eee1b5201c3d3..1f69e48b15014405f96f53cf58f37ff2524ce3ba 100644 (file)
--- a/net/socket.c
+++ b/net/socket.c
@@ -524,7 +524,7 @@ int sockfs_setattr(struct dentry *dentry, struct iattr *iattr)
 {
        int err = simple_setattr(dentry, iattr);
 
-       if (!err) {
+       if (!err && (iattr->ia_valid & ATTR_UID)) {
                struct socket *sock = SOCKET_I(d_inode(dentry));
 
                sock->sk->sk_uid = iattr->ia_uid;