Re: [PATCH net] l2tp: Serialize access to sk_user_data with sock lock

[Tom Parkin <tparkin@katalix.com>]

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On  Fri, Aug 12, 2022 at 11:54:43 +0200, Jakub Sitnicki wrote:
> On Thu, Aug 11, 2022 at 10:23 AM -07, Jakub Kicinski wrote:
> > On Wed, 10 Aug 2022 12:28:48 +0200 Jakub Sitnicki wrote:
> >> Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
> >
> > That tag immediately sets off red flags. Please find the commit where
> > to code originates, not where it was last moved.
> 
> The code move happened in v2.6.35. There's no point in digging further, IMHO.

At the time of fd558d186df2, sk_user_data was checked/set by the newly
added function l2tp_tunnel_create.  The only callpath for
l2tp_tunnel_create was via.  pppol2tp_connect which called
l2tp_tunnel_create with lock_sock held (and indeed still does).

I think the addition of the netlink API (which added a new callpath
for l2tp_tunnel_create via. l2tp_nl_cmd_tunnel_create which was *not*
lock_sock-protected) is perhaps the right commit to point to?

309795f4bec2 ("l2tp: Add netlink control API for L2TP")

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