4.9-stable review patch. If anyone has any objections, please let me know.
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From: "Jason A. Donenfeld" Jason@zx2c4.com
[ 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 | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)
--- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -2207,16 +2207,17 @@ int __netlink_dump_start(struct sock *ss cb->min_dump_alloc = control->min_dump_alloc; cb->skb = skb;
+ if (cb->start) { + ret = cb->start(cb); + if (ret) + goto error_unlock; + } + nlk->cb_running = true;
mutex_unlock(nlk->cb_mutex);
- ret = 0; - if (cb->start) - ret = cb->start(cb); - - if (!ret) - ret = netlink_dump(sk); + ret = netlink_dump(sk);
sock_put(sk);