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authorSean Tranchetti <stranche@codeaurora.org>2020-06-30 20:50:17 +0300
committerDavid S. Miller <davem@davemloft.net>2020-07-02 01:49:11 +0300
commit1e82a62fec613844da9e558f3493540a5b7a7b67 (patch)
treeef24bd75739f80865d3ed9c2aa3bfda459736b5b /net/netlink
parentd3c54f7f18cb82283777998c4bec52e49241c783 (diff)
downloadlinux-1e82a62fec613844da9e558f3493540a5b7a7b67.tar.xz
genetlink: remove genl_bind
A potential deadlock can occur during registering or unregistering a new generic netlink family between the main nl_table_lock and the cb_lock where each thread wants the lock held by the other, as demonstrated below. 1) Thread 1 is performing a netlink_bind() operation on a socket. As part of this call, it will call netlink_lock_table(), incrementing the nl_table_users count to 1. 2) Thread 2 is registering (or unregistering) a genl_family via the genl_(un)register_family() API. The cb_lock semaphore will be taken for writing. 3) Thread 1 will call genl_bind() as part of the bind operation to handle subscribing to GENL multicast groups at the request of the user. It will attempt to take the cb_lock semaphore for reading, but it will fail and be scheduled away, waiting for Thread 2 to finish the write. 4) Thread 2 will call netlink_table_grab() during the (un)registration call. However, as Thread 1 has incremented nl_table_users, it will not be able to proceed, and both threads will be stuck waiting for the other. genl_bind() is a noop, unless a genl_family implements the mcast_bind() function to handle setting up family-specific multicast operations. Since no one in-tree uses this functionality as Cong pointed out, simply removing the genl_bind() function will remove the possibility for deadlock, as there is no attempt by Thread 1 above to take the cb_lock semaphore. Fixes: c380d9a7afff ("genetlink: pass multicast bind/unbind to families") Suggested-by: Cong Wang <xiyou.wangcong@gmail.com> Acked-by: Johannes Berg <johannes.berg@intel.com> Reported-by: kernel test robot <lkp@intel.com> Signed-off-by: Sean Tranchetti <stranche@codeaurora.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/netlink')
-rw-r--r--net/netlink/genetlink.c49
1 files changed, 0 insertions, 49 deletions
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index a914b9365a46..9395ee8a868d 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -1144,60 +1144,11 @@ static struct genl_family genl_ctrl __ro_after_init = {
.netnsok = true,
};
-static int genl_bind(struct net *net, int group)
-{
- struct genl_family *f;
- int err = -ENOENT;
- unsigned int id;
-
- down_read(&cb_lock);
-
- idr_for_each_entry(&genl_fam_idr, f, id) {
- if (group >= f->mcgrp_offset &&
- group < f->mcgrp_offset + f->n_mcgrps) {
- int fam_grp = group - f->mcgrp_offset;
-
- if (!f->netnsok && net != &init_net)
- err = -ENOENT;
- else if (f->mcast_bind)
- err = f->mcast_bind(net, fam_grp);
- else
- err = 0;
- break;
- }
- }
- up_read(&cb_lock);
-
- return err;
-}
-
-static void genl_unbind(struct net *net, int group)
-{
- struct genl_family *f;
- unsigned int id;
-
- down_read(&cb_lock);
-
- idr_for_each_entry(&genl_fam_idr, f, id) {
- if (group >= f->mcgrp_offset &&
- group < f->mcgrp_offset + f->n_mcgrps) {
- int fam_grp = group - f->mcgrp_offset;
-
- if (f->mcast_unbind)
- f->mcast_unbind(net, fam_grp);
- break;
- }
- }
- up_read(&cb_lock);
-}
-
static int __net_init genl_pernet_init(struct net *net)
{
struct netlink_kernel_cfg cfg = {
.input = genl_rcv,
.flags = NL_CFG_F_NONROOT_RECV,
- .bind = genl_bind,
- .unbind = genl_unbind,
};
/* we'll bump the group number right afterwards */