[PATCH wayland] connection: Don't write past the end of the connection buffer

[Kristian Høgsberg]

On Thu, Apr 17, 2014 at 06:20:37PM +0300, Ander Conselvan de Oliveira wrote:
> From: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira at intel.com>
> 
> If a message was too big to fit in the connection buffer, the code
> in wl_buffer_put would just write past the end of it.
> 
> I haven't seen any real world use case that would trigger this bug, but
> it was possible to trigger it by sending a long enough string to the
> wl_data_source.offer request.
> 
> https://bugs.freedesktop.org/show_bug.cgi?id=69267

Right, that looks fine.  I've been debating whether we should allow
arbitrary size strings, but I think it's reasonable to cap the size.
If you're doing a protocol where a string my exceed the protocol buffer
size you should be using mmap buffers instead.  The protocol was not
designed for bulk data transfer.

Kristian

> ---
>  src/connection.c        | 25 +++++++++++++++++--------
>  tests/connection-test.c | 37 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 54 insertions(+), 8 deletions(-)
> 
> diff --git a/src/connection.c b/src/connection.c
> index 40a2182..63b0592 100644
> --- a/src/connection.c
> +++ b/src/connection.c
> @@ -61,11 +61,18 @@ struct wl_connection {
>  	int want_flush;
>  };
>  
> -static void
> +static int
>  wl_buffer_put(struct wl_buffer *b, const void *data, size_t count)
>  {
>  	uint32_t head, size;
>  
> +	if (count > sizeof(b->data)) {
> +		wl_log("Data too big for buffer (%d > %d).\n",
> +		       count, sizeof(b->data));
> +		errno = E2BIG;
> +		return -1;
> +	}
> +
>  	head = MASK(b->head);
>  	if (head + count <= sizeof b->data) {
>  		memcpy(b->data + head, data, count);
> @@ -76,6 +83,8 @@ wl_buffer_put(struct wl_buffer *b, const void *data, size_t count)
>  	}
>  
>  	b->head += count;
> +
> +	return 0;
>  }
>  
>  static void
> @@ -243,8 +252,8 @@ decode_cmsg(struct wl_buffer *buffer, struct msghdr *msg)
>  			size /= sizeof(int32_t);
>  			for (i = 0; i < size; i++)
>  				close(((int*)CMSG_DATA(cmsg))[i]);
> -		} else {
> -			wl_buffer_put(buffer, CMSG_DATA(cmsg), size);
> +		} else if (wl_buffer_put(buffer, CMSG_DATA(cmsg), size) < 0) {
> +				return -1;
>  		}
>  	}
>  
> @@ -350,7 +359,9 @@ wl_connection_write(struct wl_connection *connection,
>  			return -1;
>  	}
>  
> -	wl_buffer_put(&connection->out, data, count);
> +	if (wl_buffer_put(&connection->out, data, count) < 0)
> +		return -1;
> +
>  	connection->want_flush = 1;
>  
>  	return 0;
> @@ -367,7 +378,7 @@ wl_connection_queue(struct wl_connection *connection,
>  			return -1;
>  	}
>  
> -	wl_buffer_put(&connection->out, data, count);
> +	return wl_buffer_put(&connection->out, data, count);
>  
>  	return 0;
>  }
> @@ -394,9 +405,7 @@ wl_connection_put_fd(struct wl_connection *connection, int32_t fd)
>  			return -1;
>  	}
>  
> -	wl_buffer_put(&connection->fds_out, &fd, sizeof fd);
> -
> -	return 0;
> +	return wl_buffer_put(&connection->fds_out, &fd, sizeof fd);
>  }
>  
>  const char *
> diff --git a/tests/connection-test.c b/tests/connection-test.c
> index 52d235d..1213875 100644
> --- a/tests/connection-test.c
> +++ b/tests/connection-test.c
> @@ -235,6 +235,27 @@ expected_fail_marshal(int expected_error, const char *format, ...)
>  	assert(errno == expected_error);
>  }
>  
> +static void
> +expected_fail_marshal_send(struct marshal_data *data, int expected_error,
> +			   const char *format, ...)
> +{
> +	struct wl_closure *closure;
> +	static const uint32_t opcode = 4444;
> +	static struct wl_object sender = { NULL, NULL, 1234 };
> +	struct wl_message message = { "test", format, NULL };
> +	va_list ap;
> +
> +	va_start(ap, format);
> +	closure = wl_closure_vmarshal(&sender, opcode, ap, &message);
> +	va_end(ap);
> +
> +	assert(closure);
> +	assert(wl_closure_send(closure, data->write_connection) < 0);
> +	assert(errno == expected_error);
> +
> +	wl_closure_destroy(closure);
> +}
> +
>  TEST(connection_marshal_nullables)
>  {
>  	struct marshal_data data;
> @@ -490,6 +511,22 @@ TEST(connection_marshal_alot)
>  	release_marshal_data(&data);
>  }
>  
> +TEST(connection_marshal_too_big)
> +{
> +	struct marshal_data data;
> +	char *big_string = malloc(5000);
> +
> +	memset(big_string, ' ', 4999);
> +	big_string[4999] = '\0';
> +
> +	setup_marshal_data(&data);
> +
> +	expected_fail_marshal_send(&data, E2BIG, "s", big_string);
> +
> +	release_marshal_data(&data);
> +	free(big_string);
> +}
> +
>  static void
>  marshal_helper(const char *format, void *handler, ...)
>  {
> -- 
> 1.8.3.2
> 
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