net: make NET_(DEV|NS)_REFCNT_TRACKER depend on NET

It makes little sense to ask if networking namespace or net device refcount
tracking shall be enabled for debug kernel builds without network support.

This is similar to the commit eb0b39efb7d9 ("net: CONFIG_DEBUG_NET depends
on CONFIG_NET").

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20220915124256.32512-1-lukas.bulwahn@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net: CONFIG_DEBUG_NET depends on CONFIG_NET

It makes little sense to debug networking stacks
if networking is not compiled in.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net: add CONFIG_DEBUG_NET

This config option enables network debugging checks.

This patch adds DEBUG_NET_WARN_ON_ONCE(cond)
Note that this is not a replacement for WARN_ON_ONCE(cond)
as (cond) is not evaluated if CONFIG_DEBUG_NET is not set.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net: add networking namespace refcount tracker

We have 100+ syzbot reports about netns being dismantled too soon,
still unresolved as of today.

We think a missing get_net() or an extra put_net() is the root cause.

In order to find the bug(s), and be able to spot future ones,
this patch adds CONFIG_NET_NS_REFCNT_TRACKER and new helpers
to precisely pair all put_net() with corresponding get_net().

To use these helpers, each data structure owning a refcount
should also use a "netns_tracker" to pair the get and put.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net: add net device refcount tracker infrastructure

net device are refcounted. Over the years we had numerous bugs
caused by imbalanced dev_hold() and dev_put() calls.

The general idea is to be able to precisely pair each decrement with
a corresponding prior increment. Both share a cookie, basically
a pointer to private data storing stack traces.

This patch adds dev_hold_track() and dev_put_track().

To use these helpers, each data structure owning a refcount
should also use a "netdevice_tracker" to pair the hold and put.

netdevice_tracker dev_tracker;
...
dev_hold_track(dev, &dev_tracker, GFP_ATOMIC);
...
dev_put_track(dev, &dev_tracker);

Whenever a leak happens, we will get precise stack traces
of the point dev_hold_track() happened, at device dismantle phase.

We will also get a stack trace if too many dev_put_track() for the same
netdevice_tracker are attempted.

This is guarded by CONFIG_NET_DEV_REFCNT_TRACKER option.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>