diff options
| author | Florian Westphal <fw@strlen.de> | 2021-04-16 21:29:13 +0200 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2021-04-16 17:01:04 -0700 |
| commit | f2764bd4f6a8dffaec3e220728385d9756b3c2cb (patch) | |
| tree | 23600181883a422fbe145e849744dd39246273db | |
| parent | b02265429681c9c827c45978a61a9f00be5ea9aa (diff) | |
netlink: don't call ->netlink_bind with table lock held
When I added support to allow generic netlink multicast groups to be
restricted to subscribers with CAP_NET_ADMIN I was unaware that a
genl_bind implementation already existed in the past.
It was reverted due to ABBA deadlock:
1. ->netlink_bind gets called with the table lock held.
2. genetlink bind callback is invoked, it grabs the genl lock.
But when a new genl subsystem is (un)registered, these two locks are
taken in reverse order.
One solution would be to revert again and add a comment in genl
referring 1e82a62fec613, "genetlink: remove genl_bind").
This would need a second change in mptcp to not expose the raw token
value anymore, e.g. by hashing the token with a secret key so userspace
can still associate subflow events with the correct mptcp connection.
However, Paolo Abeni reminded me to double-check why the netlink table is
locked in the first place.
I can't find one. netlink_bind() is already called without this lock
when userspace joins a group via NETLINK_ADD_MEMBERSHIP setsockopt.
Same holds for the netlink_unbind operation.
Digging through the history, commit f773608026ee1
("netlink: access nlk groups safely in netlink bind and getname")
expanded the lock scope.
commit 3a20773beeeeade ("net: netlink: cap max groups which will be considered in netlink_bind()")
... removed the nlk->ngroups access that the lock scope
extension was all about.
Reduce the lock scope again and always call ->netlink_bind without
the table lock.
The Fixes tag should be vs. the patch mentioned in the link below,
but that one got squash-merged into the patch that came earlier in the
series.
Fixes: 4d54cc32112d8d ("mptcp: avoid lock_fast usage in accept path")
Link: https://lore.kernel.org/mptcp/20210213000001.379332-8-mathew.j.martineau@linux.intel.com/T/#u
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Xin Long <lucien.xin@gmail.com>
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: Sean Tranchetti <stranche@codeaurora.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
| -rw-r--r-- | net/netlink/af_netlink.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index dd488938447f..3a62f97acf39 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -1019,7 +1019,6 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr, return -EINVAL; } - netlink_lock_table(); if (nlk->netlink_bind && groups) { int group; @@ -1031,13 +1030,14 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr, if (!err) continue; netlink_undo_bind(group, groups, sk); - goto unlock; + return err; } } /* No need for barriers here as we return to user-space without * using any of the bound attributes. */ + netlink_lock_table(); if (!bound) { err = nladdr->nl_pid ? netlink_insert(sk, nladdr->nl_pid) : |