Enable -Wnull-dereference (GCC >=6.1), and fix the easy cases

This warning, IIUC, means that the compiler doesn't like it when it
sees a NULL check _after_ we've already dereferenced the
variable. In such cases, it considers itself free to eliminate the
NULL check.

There are a couple of tricky cases:

One was the case related to the fact that tor_addr_to_in6() can
return NULL if it gets a non-AF_INET6 address.  The fix was to
create a variant which asserts on the address type, and never
returns NULL.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/or/channeltls.c b/src/or/channeltls.c
index 2128b0924d..293f01070b 100644
--- a/src/or/channeltls.c
+++ b/src/or/channeltls.c
@@ -797,6 +797,7 @@ static int
 channel_tls_write_packed_cell_method(channel_t *chan,
                                      packed_cell_t *packed_cell)
 {
+  tor_assert(chan);
   channel_tls_t *tlschan = BASE_CHAN_TO_TLS(chan);
   size_t cell_network_size = get_cell_network_size(chan->wide_circ_ids);
   int written = 0;