| Message ID | 20210416192913.6139-1-fw@strlen.de (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | f2764bd4f6a8dffaec3e220728385d9756b3c2cb |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net] netlink: don't call ->netlink_bind with table lock held | expand |
Hello: This patch was applied to netdev/net.git (refs/heads/master): On Fri, 16 Apr 2021 21:29:13 +0200 you wrote: > 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. > > [...] Here is the summary with links: - [net] netlink: don't call ->netlink_bind with table lock held https://git.kernel.org/netdev/net/c/f2764bd4f6a8 You are awesome, thank you! -- Deet-doot-dot, I am a bot. https://korg.docs.kernel.org/patchwork/pwbot.html
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) :
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> --- net/netlink/af_netlink.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)