From 5c398dc8f5a58b5417d8ae0d474704feb6e12a12 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sun, 24 Oct 2010 04:27:10 +0000 Subject: netlink: fix netlink_change_ngroups() commit 6c04bb18ddd633 (netlink: use call_rcu for netlink_change_ngroups) used a somewhat convoluted and racy way to perform call_rcu(). The old block of memory is freed after a grace period, but the rcu_head used to track it is located in new block. This can clash if we call two times or more netlink_change_ngroups(), and a block is freed before another. call_rcu() called on different cpus makes no guarantee in order of callbacks. Fix this using a more standard way of handling this : Each block of memory contains its own rcu_head, so that no 'use after free' can happens. Signed-off-by: Eric Dumazet CC: Johannes Berg CC: Paul E. McKenney Signed-off-by: David S. Miller --- net/netlink/af_netlink.c | 65 ++++++++++++++++++------------------------------ 1 file changed, 24 insertions(+), 41 deletions(-) (limited to 'net/netlink') diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index cd96ed3ccee4..478181d53c55 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -83,9 +83,9 @@ struct netlink_sock { struct module *module; }; -struct listeners_rcu_head { - struct rcu_head rcu_head; - void *ptr; +struct listeners { + struct rcu_head rcu; + unsigned long masks[0]; }; #define NETLINK_KERNEL_SOCKET 0x1 @@ -119,7 +119,7 @@ struct nl_pid_hash { struct netlink_table { struct nl_pid_hash hash; struct hlist_head mc_list; - unsigned long *listeners; + struct listeners __rcu *listeners; unsigned int nl_nonroot; unsigned int groups; struct mutex *cb_mutex; @@ -338,7 +338,7 @@ netlink_update_listeners(struct sock *sk) if (i < NLGRPLONGS(nlk_sk(sk)->ngroups)) mask |= nlk_sk(sk)->groups[i]; } - tbl->listeners[i] = mask; + tbl->listeners->masks[i] = mask; } /* this function is only called with the netlink table "grabbed", which * makes sure updates are visible before bind or setsockopt return. */ @@ -936,7 +936,7 @@ EXPORT_SYMBOL(netlink_unicast); int netlink_has_listeners(struct sock *sk, unsigned int group) { int res = 0; - unsigned long *listeners; + struct listeners *listeners; BUG_ON(!netlink_is_kernel(sk)); @@ -944,7 +944,7 @@ int netlink_has_listeners(struct sock *sk, unsigned int group) listeners = rcu_dereference(nl_table[sk->sk_protocol].listeners); if (group - 1 < nl_table[sk->sk_protocol].groups) - res = test_bit(group - 1, listeners); + res = test_bit(group - 1, listeners->masks); rcu_read_unlock(); @@ -1498,7 +1498,7 @@ netlink_kernel_create(struct net *net, int unit, unsigned int groups, struct socket *sock; struct sock *sk; struct netlink_sock *nlk; - unsigned long *listeners = NULL; + struct listeners *listeners = NULL; BUG_ON(!nl_table); @@ -1523,8 +1523,7 @@ netlink_kernel_create(struct net *net, int unit, unsigned int groups, if (groups < 32) groups = 32; - listeners = kzalloc(NLGRPSZ(groups) + sizeof(struct listeners_rcu_head), - GFP_KERNEL); + listeners = kzalloc(sizeof(*listeners) + NLGRPSZ(groups), GFP_KERNEL); if (!listeners) goto out_sock_release; @@ -1541,7 +1540,7 @@ netlink_kernel_create(struct net *net, int unit, unsigned int groups, netlink_table_grab(); if (!nl_table[unit].registered) { nl_table[unit].groups = groups; - nl_table[unit].listeners = listeners; + rcu_assign_pointer(nl_table[unit].listeners, listeners); nl_table[unit].cb_mutex = cb_mutex; nl_table[unit].module = module; nl_table[unit].registered = 1; @@ -1572,43 +1571,28 @@ netlink_kernel_release(struct sock *sk) EXPORT_SYMBOL(netlink_kernel_release); -static void netlink_free_old_listeners(struct rcu_head *rcu_head) +static void listeners_free_rcu(struct rcu_head *head) { - struct listeners_rcu_head *lrh; - - lrh = container_of(rcu_head, struct listeners_rcu_head, rcu_head); - kfree(lrh->ptr); + kfree(container_of(head, struct listeners, rcu)); } int __netlink_change_ngroups(struct sock *sk, unsigned int groups) { - unsigned long *listeners, *old = NULL; - struct listeners_rcu_head *old_rcu_head; + struct listeners *new, *old; struct netlink_table *tbl = &nl_table[sk->sk_protocol]; if (groups < 32) groups = 32; if (NLGRPSZ(tbl->groups) < NLGRPSZ(groups)) { - listeners = kzalloc(NLGRPSZ(groups) + - sizeof(struct listeners_rcu_head), - GFP_ATOMIC); - if (!listeners) + new = kzalloc(sizeof(*new) + NLGRPSZ(groups), GFP_ATOMIC); + if (!new) return -ENOMEM; - old = tbl->listeners; - memcpy(listeners, old, NLGRPSZ(tbl->groups)); - rcu_assign_pointer(tbl->listeners, listeners); - /* - * Free the old memory after an RCU grace period so we - * don't leak it. We use call_rcu() here in order to be - * able to call this function from atomic contexts. The - * allocation of this memory will have reserved enough - * space for struct listeners_rcu_head at the end. - */ - old_rcu_head = (void *)(tbl->listeners + - NLGRPLONGS(tbl->groups)); - old_rcu_head->ptr = old; - call_rcu(&old_rcu_head->rcu_head, netlink_free_old_listeners); + old = rcu_dereference_raw(tbl->listeners); + memcpy(new->masks, old->masks, NLGRPSZ(tbl->groups)); + rcu_assign_pointer(tbl->listeners, new); + + call_rcu(&old->rcu, listeners_free_rcu); } tbl->groups = groups; @@ -2104,18 +2088,17 @@ static void __net_exit netlink_net_exit(struct net *net) static void __init netlink_add_usersock_entry(void) { - unsigned long *listeners; + struct listeners *listeners; int groups = 32; - listeners = kzalloc(NLGRPSZ(groups) + sizeof(struct listeners_rcu_head), - GFP_KERNEL); + listeners = kzalloc(sizeof(*listeners) + NLGRPSZ(groups), GFP_KERNEL); if (!listeners) - panic("netlink_add_usersock_entry: Cannot allocate listneres\n"); + panic("netlink_add_usersock_entry: Cannot allocate listeners\n"); netlink_table_grab(); nl_table[NETLINK_USERSOCK].groups = groups; - nl_table[NETLINK_USERSOCK].listeners = listeners; + rcu_assign_pointer(nl_table[NETLINK_USERSOCK].listeners, listeners); nl_table[NETLINK_USERSOCK].module = THIS_MODULE; nl_table[NETLINK_USERSOCK].registered = 1; -- cgit v1.2.3-59-g8ed1b