Hello,
Here's an updated version of Herbert's patch which always uses
load_acquire through a helper.
Thanks.
----- 8< -----
The commit 1f770c0a09da855a2b51af6d19de97fb955eca85 ("netlink: Fix
autobind race condition that leads to zero port ID") created some new
races that can occur due to inconsistencies between the two port IDs -
a reader may see zero nlk->portid after seeing non-zero
nlk->rhash_portid.
This patch reverts the original patch and instead uses a load_acquire
protected boolean to indicate that a user netlink socket has been
bound. The boolean is set with store_release only after the portid is
assigned and the socket is hashed. The readers test with load_acquire
so that the socket is guaranteed to be visible with a valid port
number and hashed on a true return.
As this sort of lockless tests can be broken in ways which are very
difficult to track down, the boolean field is prefixed with double
underscores and a dedicated test helper with load_acquire is always
used. While a couple test sites might not strictly require
load_acquire, micro-optimization at this level doens't make sense
given the danger of subtle breakages.
tj: Took Herbert's patch and updated so that all readers test via a
helper which does load_acquire.
Fixes: 1f770c0a09da ("netlink: Fix autobind race condition that leads to zero
port ID")
Reported-by: Tejun Heo <t...@kernel.org>
Reported-by: Linus Torvalds <torva...@linux-foundation.org>
Original-patch-by: Herbert Xu <herb...@gondor.apana.org.au>
Signed-off-by: Tejun Heo <t...@kernel.org>
---
net/netlink/af_netlink.c | 24 ++++++++++++++----------
net/netlink/af_netlink.h | 20 +++++++++++++++++++-
2 files changed, 33 insertions(+), 11 deletions(-)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1015,7 +1015,7 @@ static inline int netlink_compare(struct
const struct netlink_compare_arg *x = arg->key;
const struct netlink_sock *nlk = ptr;
- return nlk->rhash_portid != x->portid ||
+ return nlk->portid != x->portid ||
!net_eq(sock_net(&nlk->sk), read_pnet(&x->pnet));
}
@@ -1041,7 +1041,7 @@ static int __netlink_insert(struct netli
{
struct netlink_compare_arg arg;
- netlink_compare_arg_init(&arg, sock_net(sk), nlk_sk(sk)->rhash_portid);
+ netlink_compare_arg_init(&arg, sock_net(sk), nlk_sk(sk)->portid);
return rhashtable_lookup_insert_key(&table->hash, &arg,
&nlk_sk(sk)->node,
netlink_rhashtable_params);
@@ -1095,7 +1095,7 @@ static int netlink_insert(struct sock *s
lock_sock(sk);
err = -EBUSY;
- if (nlk_sk(sk)->portid)
+ if (nlk_bound(nlk_sk(sk)))
goto err;
err = -ENOMEM;
@@ -1103,7 +1103,7 @@ static int netlink_insert(struct sock *s
unlikely(atomic_read(&table->hash.nelems) >= UINT_MAX))
goto err;
- nlk_sk(sk)->rhash_portid = portid;
+ nlk_sk(sk)->portid = portid;
sock_hold(sk);
err = __netlink_insert(table, sk);
@@ -1119,7 +1119,8 @@ static int netlink_insert(struct sock *s
goto err;
}
- nlk_sk(sk)->portid = portid;
+ /* See nlk_bound(). */
+ smp_store_release(&nlk_sk(sk)->__bound, portid);
err:
release_sock(sk);
@@ -1521,9 +1522,11 @@ static int netlink_bind(struct socket *s
return err;
}
- if (nlk->portid)
+ /* Ensure nlk->portid is up-to-date. */
+ if (nlk_bound(nlk)) {
if (nladdr->nl_pid != nlk->portid)
return -EINVAL;
+ }
if (nlk->netlink_bind && groups) {
int group;
@@ -1539,7 +1542,7 @@ static int netlink_bind(struct socket *s
}
}
- if (!nlk->portid) {
+ if (!nlk_bound(nlk)) {
err = nladdr->nl_pid ?
netlink_insert(sk, nladdr->nl_pid) :
netlink_autobind(sock);
@@ -1587,7 +1590,7 @@ static int netlink_connect(struct socket
!netlink_allowed(sock, NL_CFG_F_NONROOT_SEND))
return -EPERM;
- if (!nlk->portid)
+ if (!nlk_bound(nlk))
err = netlink_autobind(sock);
if (err == 0) {
@@ -2428,7 +2431,8 @@ static int netlink_sendmsg(struct socket
dst_group = nlk->dst_group;
}
- if (!nlk->portid) {
+ /* Ensure nlk->portid is up-to-date. */
+ if (!nlk_bound(nlk)) {
err = netlink_autobind(sock);
if (err)
goto out;
@@ -3257,7 +3261,7 @@ static inline u32 netlink_hash(const voi
const struct netlink_sock *nlk = data;
struct netlink_compare_arg arg;
- netlink_compare_arg_init(&arg, sock_net(&nlk->sk), nlk->rhash_portid);
+ netlink_compare_arg_init(&arg, sock_net(&nlk->sk), nlk->portid);
return jhash2((u32 *)&arg, netlink_compare_arg_len / sizeof(u32), seed);
}
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -3,6 +3,7 @@
#include <linux/rhashtable.h>
#include <linux/atomic.h>
+#include <asm/barrier.h>
#include <net/sock.h>
#define NLGRPSZ(x) (ALIGN(x, sizeof(unsigned long) * 8) / 8)
@@ -25,7 +26,6 @@ struct netlink_ring {
struct netlink_sock {
/* struct sock has to be the first member of netlink_sock */
struct sock sk;
- u32 rhash_portid;
u32 portid;
u32 dst_portid;
u32 dst_group;
@@ -36,6 +36,7 @@ struct netlink_sock {
unsigned long state;
size_t max_recvmsg_len;
wait_queue_head_t wait;
+ bool __bound; /* always use nlk_bound() */
bool cb_running;
struct netlink_callback cb;
struct mutex *cb_mutex;
@@ -60,6 +61,23 @@ static inline struct netlink_sock *nlk_s
return container_of(sk, struct netlink_sock, sk);
}
+/**
+ * nlk_bound - test whether a netlink_sock is bound to a port number
+ * @nlk: netlink_sock of interest
+ *
+ * Test whether @nlk is bound to a port number. Can be called without any
+ * locks and guarantees no false positive - @nlk has a valid port number
+ * and is hashed on a true return.
+ */
+static inline bool nlk_bound(struct netlink_sock *nlk)
+{
+ /*
+ * Paired with smp_store_release() in netlink_insert() to guarantee
+ * the visibility of port number and hashing.
+ */
+ return smp_load_acquire(&nlk->__bound);
+}
+
struct netlink_table {
struct rhashtable hash;
struct hlist_head mc_list;
--
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