net: write once on dev->allmulti and dev->promiscuity

In the following patch we want to read dev->allmulti
and dev->promiscuity locklessly from rtnl_fill_ifinfo()

In this patch I change __dev_set_promiscuity() and
__dev_set_allmulti() to write these fields (and dev->flags)
only if they succeed, with WRITE_ONCE() annotations.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/core/dev.c b/net/core/dev.c
index 882ce6375b2e6ba7dfaee5df4e933463aa100e5b..d9d9a0d91593c9cfdb9de5646bd55c6eefb4a370 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8544,27 +8544,29 @@ static void dev_change_rx_flags(struct net_device *dev, int flags)
 static int __dev_set_promiscuity(struct net_device *dev, int inc, bool notify)
 {
        unsigned int old_flags = dev->flags;
+       unsigned int promiscuity, flags;
        kuid_t uid;
        kgid_t gid;
 
        ASSERT_RTNL();
 
-       dev->flags |= IFF_PROMISC;
-       dev->promiscuity += inc;
-       if (dev->promiscuity == 0) {
+       promiscuity = dev->promiscuity + inc;
+       if (promiscuity == 0) {
                /*
                 * Avoid overflow.
                 * If inc causes overflow, untouch promisc and return error.
                 */
-               if (inc < 0)
-                       dev->flags &= ~IFF_PROMISC;
-               else {
-                       dev->promiscuity -= inc;
+               if (unlikely(inc > 0)) {
                        netdev_warn(dev, "promiscuity touches roof, set promiscuity failed. promiscuity feature of device might be broken.\n");
                        return -EOVERFLOW;
                }
+               flags = old_flags & ~IFF_PROMISC;
+       } else {
+               flags = old_flags | IFF_PROMISC;
        }
-       if (dev->flags != old_flags) {
+       WRITE_ONCE(dev->promiscuity, promiscuity);
+       if (flags != old_flags) {
+               WRITE_ONCE(dev->flags, flags);
                netdev_info(dev, "%s promiscuous mode\n",
                            dev->flags & IFF_PROMISC ? "entered" : "left");
                if (audit_enabled) {
@@ -8615,25 +8617,27 @@ EXPORT_SYMBOL(dev_set_promiscuity);
 static int __dev_set_allmulti(struct net_device *dev, int inc, bool notify)
 {
        unsigned int old_flags = dev->flags, old_gflags = dev->gflags;
+       unsigned int allmulti, flags;
 
        ASSERT_RTNL();
 
-       dev->flags |= IFF_ALLMULTI;
-       dev->allmulti += inc;
-       if (dev->allmulti == 0) {
+       allmulti = dev->allmulti + inc;
+       if (allmulti == 0) {
                /*
                 * Avoid overflow.
                 * If inc causes overflow, untouch allmulti and return error.
                 */
-               if (inc < 0)
-                       dev->flags &= ~IFF_ALLMULTI;
-               else {
-                       dev->allmulti -= inc;
+               if (unlikely(inc > 0)) {
                        netdev_warn(dev, "allmulti touches roof, set allmulti failed. allmulti feature of device might be broken.\n");
                        return -EOVERFLOW;
                }
+               flags = old_flags & ~IFF_ALLMULTI;
+       } else {
+               flags = old_flags | IFF_ALLMULTI;
        }
-       if (dev->flags ^ old_flags) {
+       WRITE_ONCE(dev->allmulti, allmulti);
+       if (flags != old_flags) {
+               WRITE_ONCE(dev->flags, flags);
                netdev_info(dev, "%s allmulticast mode\n",
                            dev->flags & IFF_ALLMULTI ? "entered" : "left");
                dev_change_rx_flags(dev, IFF_ALLMULTI);