RAVENPLAT 2378:OSS vulnerability found in [boot.img]:[linux_kernel] (CVE-2018-9517...

RAVENPLAT 2378:OSS vulnerability found in [boot.img]:[linux_kernel] (CVE-2018-9517) Risk:[] [1/1]

PD#OTT-5666

[Problem]
In pppol2tp_connect, there is possible memory corruption due to a
use after free. This could lead to local escalation of privilege with
System execution privileges needed. User interaction is not needed for
exploitation.

[Solution]
l2tp: pass tunnel pointer to ->session_create()

Using l2tp_tunnel_find() in pppol2tp_session_create() and
l2tp_eth_create() is racy, because no reference is held on the
returned session. These functions are only used to implement the
->session_create callback which is run by l2tp_nl_cmd_session_create().
Therefore searching for the parent tunnel isn't necessary because
l2tp_nl_cmd_session_create() already has a pointer to it and holds a
reference.

This patch modifies ->session_create()'s prototype to directly pass the
the parent tunnel as parameter, thus avoiding searching for it in
pppol2tp_session_create() and l2tp_eth_create().

Since we have to touch the ->session_create() call in
l2tp_nl_cmd_session_create(), let's also remove the useless conditional:
we know that ->session_create isn't NULL at this point because it's
already been checked earlier in this same function.

Finally, one might be tempted to think that the removed
l2tp_tunnel_find() calls were harmless because they would return the
same tunnel as the one held by l2tp_nl_cmd_session_create() anyway.
But that tunnel might be removed and a new one created with same tunnel
Id before the l2tp_tunnel_find() call. In this case l2tp_tunnel_find()
	would return the new tunnel which wouldn't be protected by the
	reference held by l2tp_nl_cmd_session_create().

Change-Id: I50e19ae5abb4009205e59105222bf92e3587f9c4
Signed-off-by: Hanjie Lin <hanjie.lin@amlogic.com>