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SubjectRe: 2.6.38-rc1: arp triggers RTNL assertion
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Le vendredi 21 janvier 2011 à 13:06 -0800, David Miller a écrit :
> From: Eric Dumazet <eric.dumazet@gmail.com>
> Date: Fri, 21 Jan 2011 19:52:56 +0100
>
> > Here is how I fixed this, thanks again Jamie !
> >
> > [PATCH] net: neighbour: pneigh_lookup() doesnt need RTNL
>
> Eric, I don't think we can do this.
>
> Fundamentally, any time a user operation changes the configuration
> of the networking, we must hold the RTNL.
>
> Eliding the RTNL for lookups is fine, but for things that change
> state it is not.
>
> I therefore think you'll need to rework the arp_ioctl() portions
> of the commit that introduced this regression.
>

Here is a second try of the fix, thanks !

Note : Tested with CONFIG_PROVE_RCU=y

[PATCH] net: arp_ioctl() must hold RTNL

Commit 941666c2e3e0 "net: RCU conversion of dev_getbyhwaddr() and
arp_ioctl()" introduced a regression, reported by Jamie Heilman.
"arp -Ds 192.168.2.41 eth0 pub" triggered the ASSERT_RTNL() assert
in pneigh_lookup()

Removing RTNL requirement from arp_ioctl() was a mistake, just revert
that part.

Reported-by: Jamie Heilman <jamie@audible.transient.net>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
net/core/dev.c | 3 ++-
net/ipv4/arp.c | 11 +++++------
2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 7c6a46f..24ea2d7 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -749,7 +749,8 @@ EXPORT_SYMBOL(dev_get_by_index);
* @ha: hardware address
*
* Search for an interface by MAC address. Returns NULL if the device
- * is not found or a pointer to the device. The caller must hold RCU
+ * is not found or a pointer to the device.
+ * The caller must hold RCU or RTNL.
* The returned device has not had its ref count increased
* and the caller must therefore be careful about locking
*
diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 04c8b69..7927589 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -1017,14 +1017,13 @@ static int arp_req_set_proxy(struct net *net, struct net_device *dev, int on)
IPV4_DEVCONF_ALL(net, PROXY_ARP) = on;
return 0;
}
- if (__in_dev_get_rcu(dev)) {
- IN_DEV_CONF_SET(__in_dev_get_rcu(dev), PROXY_ARP, on);
+ if (__in_dev_get_rtnl(dev)) {
+ IN_DEV_CONF_SET(__in_dev_get_rtnl(dev), PROXY_ARP, on);
return 0;
}
return -ENXIO;
}

-/* must be called with rcu_read_lock() */
static int arp_req_set_public(struct net *net, struct arpreq *r,
struct net_device *dev)
{
@@ -1233,10 +1232,10 @@ int arp_ioctl(struct net *net, unsigned int cmd, void __user *arg)
if (!(r.arp_flags & ATF_NETMASK))
((struct sockaddr_in *)&r.arp_netmask)->sin_addr.s_addr =
htonl(0xFFFFFFFFUL);
- rcu_read_lock();
+ rtnl_lock();
if (r.arp_dev[0]) {
err = -ENODEV;
- dev = dev_get_by_name_rcu(net, r.arp_dev);
+ dev = __dev_get_by_name(net, r.arp_dev);
if (dev == NULL)
goto out;

@@ -1263,7 +1262,7 @@ int arp_ioctl(struct net *net, unsigned int cmd, void __user *arg)
break;
}
out:
- rcu_read_unlock();
+ rtnl_unlock();
if (cmd == SIOCGARP && !err && copy_to_user(arg, &r, sizeof(r)))
err = -EFAULT;
return err;

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