socket: close race condition between sock_close() and sockfs_setattr() (6d8c50dc) · Commits · 戴 / test

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: ("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

+15 −3

Original line number	Original line	Diff line number	Diff line
	@@ -541,7 +541,10 @@ static int sockfs_setattr(struct dentry dentry, struct iattr iattr)
	if (!err && (iattr->ia_valid & ATTR_UID)) {		if (!err && (iattr->ia_valid & ATTR_UID)) {
	struct socket *sock = SOCKET_I(d_inode(dentry));		struct socket *sock = SOCKET_I(d_inode(dentry));

			if (sock->sk)
	sock->sk->sk_uid = iattr->ia_uid;		sock->sk->sk_uid = iattr->ia_uid;
			else
			err = -ENOENT;
	}		}

	return err;		return err;
	@@ -590,12 +593,16 @@ EXPORT_SYMBOL(sock_alloc);
	* an inode not a file.		* an inode not a file.
	*/		*/

	void sock_release(struct socket *sock)		static void __sock_release(struct socket sock, struct inode inode)
	{		{
	if (sock->ops) {		if (sock->ops) {
	struct module *owner = sock->ops->owner;		struct module *owner = sock->ops->owner;

			if (inode)
			inode_lock(inode);
	sock->ops->release(sock);		sock->ops->release(sock);
			if (inode)
			inode_unlock(inode);
	sock->ops = NULL;		sock->ops = NULL;
	module_put(owner);		module_put(owner);
	}		}
	@@ -609,6 +616,11 @@ void sock_release(struct socket *sock)
	}		}
	sock->file = NULL;		sock->file = NULL;
	}		}

			void sock_release(struct socket *sock)
			{
			__sock_release(sock, NULL);
			}
	EXPORT_SYMBOL(sock_release);		EXPORT_SYMBOL(sock_release);

	void __sock_tx_timestamp(__u16 tsflags, __u8 *tx_flags)		void __sock_tx_timestamp(__u16 tsflags, __u8 *tx_flags)
	@@ -1171,7 +1183,7 @@ static int sock_mmap(struct file file, struct vm_area_struct vma)

	static int sock_close(struct inode inode, struct file filp)		static int sock_close(struct inode inode, struct file filp)
	{		{
	sock_release(SOCKET_I(inode));		__sock_release(SOCKET_I(inode), inode);
	return 0;		return 0;
	}		}

Admin message