From: Sean Tranchetti stranche@codeaurora.org
[ Upstream commit 1e82a62fec613844da9e558f3493540a5b7a7b67 ]
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/net/genetlink.h | 8 ------- net/netlink/genetlink.c | 52 ------------------------------------------------ 2 files changed, 60 deletions(-)
--- a/include/net/genetlink.h +++ b/include/net/genetlink.h @@ -33,12 +33,6 @@ struct genl_info; * do additional, common, filtering and return an error * @post_doit: called after an operation's doit callback, it may * undo operations done by pre_doit, for example release locks - * @mcast_bind: a socket bound to the given multicast group (which - * is given as the offset into the groups array) - * @mcast_unbind: a socket was unbound from the given multicast group. - * Note that unbind() will not be called symmetrically if the - * generic netlink family is removed while there are still open - * sockets. * @attrbuf: buffer to store parsed attributes * @family_list: family list * @mcgrps: multicast groups used by this family (private) @@ -61,8 +55,6 @@ struct genl_family { void (*post_doit)(const struct genl_ops *ops, struct sk_buff *skb, struct genl_info *info); - int (*mcast_bind)(struct net *net, int group); - void (*mcast_unbind)(struct net *net, int group); struct nlattr ** attrbuf; /* private */ const struct genl_ops * ops; /* private */ const struct genl_multicast_group *mcgrps; /* private */ --- a/net/netlink/genetlink.c +++ b/net/netlink/genetlink.c @@ -992,63 +992,11 @@ static const struct genl_multicast_group { .name = "notify", }, };
-static int genl_bind(struct net *net, int group) -{ - int i, err = -ENOENT; - - down_read(&cb_lock); - for (i = 0; i < GENL_FAM_TAB_SIZE; i++) { - struct genl_family *f; - - list_for_each_entry(f, genl_family_chain(i), family_list) { - 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) -{ - int i; - - down_read(&cb_lock); - for (i = 0; i < GENL_FAM_TAB_SIZE; i++) { - struct genl_family *f; - - list_for_each_entry(f, genl_family_chain(i), family_list) { - 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 */