APPLIED[Bionic]: [SRU][A/B]PATCH 1/1] socket: close race condition between sock_close() and sockfs_setattr()

[Kleber Souza]

On 07/05/18 06:04, Khalid Elmously wrote:
> From: Cong Wang <xiyou.wangcong at gmail.com>
> 
> 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 at gmail.com>
> Cc: Tetsuo Handa <penguin-kernel at i-love.sakura.ne.jp>
> Cc: Lorenzo Colitti <lorenzo at google.com>
> Cc: Al Viro <viro at zeniv.linux.org.uk>
> Signed-off-by: Cong Wang <xiyou.wangcong at gmail.com>
> Signed-off-by: David S. Miller <davem at davemloft.net>
> (cherry-picked from 6d8c50dcb029872b298eea68cc6209c866fd3e14)
> Signed-off-by: Khalid Elmously <khalid.elmously at canonical.com>
> ---
>  net/socket.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/net/socket.c b/net/socket.c
> index 6f05d5c4bf30..f2957aa205e6 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -544,7 +544,10 @@ static int sockfs_setattr(struct dentry *dentry, struct iattr *iattr)
>  	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;
> @@ -594,12 +597,16 @@ 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);
>  	}
> @@ -614,6 +621,11 @@ 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)
> @@ -1128,7 +1140,7 @@ static int sock_mmap(struct file *file, struct vm_area_struct *vma)
>  
>  static int sock_close(struct inode *inode, struct file *filp)
>  {
> -	sock_release(SOCKET_I(inode));
> +	__sock_release(SOCKET_I(inode), inode);
>  	return 0;
>  }
>  
> 

Applied to bionic/master-next branch.

Thanks,
Kleber