| From foo@baz Thu Jun 21 06:54:06 JST 2018 |
| 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() |
| |
| From: Cong Wang <xiyou.wangcong@gmail.com> |
| |
| [ Upstream commit 6d8c50dcb029872b298eea68cc6209c866fd3e14 ] |
| |
| 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> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| 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; |
| } |
| |