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netlink: do not set cb_running if dump's start() errs
authorJason A. Donenfeld <Jason@zx2c4.com>
Mon, 9 Oct 2017 12:14:51 +0000 (14:14 +0200)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Sat, 18 Nov 2017 10:22:21 +0000 (11:22 +0100)
commit4cd69ad53001ae399b6474113864a4ca190498fd
treedafad5a6512d5f4642677f00cc725ce33a080cb3
parentd87890d9ff15458e7207369540a4f7449db493e4
netlink: do not set cb_running if dump's start() errs

[ Upstream commit 41c87425a1ac9b633e0fcc78eb1f19640c8fb5a0 ]

It turns out that multiple places can call netlink_dump(), which means
it's still possible to dereference partially initialized values in
dump() that were the result of a faulty returned start().

This fixes the issue by calling start() _before_ setting cb_running to
true, so that there's no chance at all of hitting the dump() function
through any indirect paths.

It also moves the call to start() to be when the mutex is held. This has
the nice side effect of serializing invocations to start(), which is
likely desirable anyway. It also prevents any possible other races that
might come out of this logic.

In testing this with several different pieces of tricky code to trigger
these issues, this commit fixes all avenues that I'm aware of.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
net/netlink/af_netlink.c