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Message-ID: <20250314010501.75798-1-kuniyu@amazon.com>
Date: Thu, 13 Mar 2025 17:59:55 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Roopa Prabhu
<roopa@...dia.com>, Nikolay Aleksandrov <razor@...ckwall.org>, "Willem de
Bruijn" <willemb@...gle.com>, Simon Horman <horms@...nel.org>
CC: Kuniyuki Iwashima <kuniyu@...zon.com>, Kuniyuki Iwashima
<kuni1840@...il.com>, <netdev@...r.kernel.org>, <bridge@...ts.linux.dev>,
syzkaller <syzkaller@...glegroups.com>, yan kang <kangyan91@...look.com>,
"yue sun" <samsun1006219@...il.com>
Subject: [PATCH v1 net] net: Remove RTNL dance for SIOCBRADDIF and SIOCBRDELIF.
SIOCBRDELIF is passed to dev_ioctl() first and later forwarded to
br_ioctl_call(), which causes unnecessary RTNL dance and the splat
below [0] under RTNL pressure.
Let's say Thread A is trying to detach a device from a bridge and
Thread B is trying to remove the bridge.
In dev_ioctl(), Thread A bumps the bridge device's refcnt by
netdev_hold() and releases RTNL because the following br_ioctl_call()
also re-acquires RTNL.
In the race window, Thread B could acquire RTNL and try to remove
the bridge device. Then, rtnl_unlock() by Thread B will release RTNL
and wait for netdev_put() by Thread A.
Thread A, however, must hold RTNL twice after the unlock in dev_ifsioc(),
which may take long under RTNL pressure, resulting in the splat by
Thread B.
Thread A (SIOCBRDELIF) Thread B (SIOCBRDELBR)
---------------------- ----------------------
sock_ioctl sock_ioctl
`- sock_do_ioctl `- br_ioctl_call
`- dev_ioctl `- br_ioctl_stub
|- rtnl_lock |
|- dev_ifsioc '
' |- dev = __dev_get_by_name(...)
|- netdev_hold(dev, ...) .
/ |- rtnl_unlock ------. |
| |- br_ioctl_call `---> |- rtnl_lock
Race | | `- br_ioctl_stub |- br_del_bridge
Window | | | |- dev = __dev_get_by_name(...)
| | | May take long | `- br_dev_delete(dev, ...)
| | | under RTNL pressure | `- unregister_netdevice_queue(dev, ...)
| | | | `- rtnl_unlock
| | |- rtnl_lock <--| `- netdev_run_todo
| | |- ... | `- netdev_run_todo
| | `- rtnl_unlock | |- __rtnl_unlock
| | | |- netdev_wait_allrefs_any
\ |- rtnl_lock <--------' |
|- netdev_put(dev, ...) <----------------' Wait refcnt decrement
and log splat below
To avoid blocking SIOCBRDELBR unnecessarily, let's not call
dev_ioctl() for SIOCBRADDIF and SIOCBRDELIF.
In the dev_ioctl() path, we do the following:
1. Copy struct ifreq by get_user_ifreq in sock_do_ioctl()
2. Check CAP_NET_ADMIN in dev_ioctl()
3. Call dev_load() in dev_ioctl()
4. Fetch the master dev from ifr.ifr_name in dev_ifsioc()
3. can be done by request_module() in br_ioctl_call(), so we move
1., 2., and 4. to br_ioctl_stub().
Note that 2. is also checked later in add_del_if(), but it's better
performed before RTNL.
SIOCBRADDIF and SIOCBRDELIF have been processed in dev_ioctl() since
the pre-git era, and there seems to be no specific reason to process
them there.
[0]:
unregister_netdevice: waiting for wpan3 to become free. Usage count = 2
ref_tracker: wpan3@...f8880662d8608 has 1/1 users at
__netdev_tracker_alloc include/linux/netdevice.h:4282 [inline]
netdev_hold include/linux/netdevice.h:4311 [inline]
dev_ifsioc+0xc6a/0x1160 net/core/dev_ioctl.c:624
dev_ioctl+0x255/0x10c0 net/core/dev_ioctl.c:826
sock_do_ioctl+0x1ca/0x260 net/socket.c:1213
sock_ioctl+0x23a/0x6c0 net/socket.c:1318
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl fs/ioctl.c:892 [inline]
__x64_sys_ioctl+0x1a4/0x210 fs/ioctl.c:892
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcb/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Fixes: 893b19587534 ("net: bridge: fix ioctl locking")
Reported-by: syzkaller <syzkaller@...glegroups.com>
Reported-by: yan kang <kangyan91@...look.com>
Reported-by: yue sun <samsun1006219@...il.com>
Closes: https://lore.kernel.org/netdev/SY8P300MB0421225D54EB92762AE8F0F2A1D32@SY8P300MB0421.AUSP300.PROD.OUTLOOK.COM/
Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
include/linux/if_bridge.h | 6 ++----
net/bridge/br_ioctl.c | 39 ++++++++++++++++++++++++++++++++++++---
net/bridge/br_private.h | 3 +--
net/core/dev_ioctl.c | 19 -------------------
net/socket.c | 19 +++++++++----------
5 files changed, 48 insertions(+), 38 deletions(-)
diff --git a/include/linux/if_bridge.h b/include/linux/if_bridge.h
index 3ff96ae31bf6..c5fe3b2a53e8 100644
--- a/include/linux/if_bridge.h
+++ b/include/linux/if_bridge.h
@@ -65,11 +65,9 @@ struct br_ip_list {
#define BR_DEFAULT_AGEING_TIME (300 * HZ)
struct net_bridge;
-void brioctl_set(int (*hook)(struct net *net, struct net_bridge *br,
- unsigned int cmd, struct ifreq *ifr,
+void brioctl_set(int (*hook)(struct net *net, unsigned int cmd,
void __user *uarg));
-int br_ioctl_call(struct net *net, struct net_bridge *br, unsigned int cmd,
- struct ifreq *ifr, void __user *uarg);
+int br_ioctl_call(struct net *net, unsigned int cmd, void __user *uarg);
#if IS_ENABLED(CONFIG_BRIDGE) && IS_ENABLED(CONFIG_BRIDGE_IGMP_SNOOPING)
int br_multicast_list_adjacent(struct net_device *dev,
diff --git a/net/bridge/br_ioctl.c b/net/bridge/br_ioctl.c
index f213ed108361..b5a607f6da4e 100644
--- a/net/bridge/br_ioctl.c
+++ b/net/bridge/br_ioctl.c
@@ -394,10 +394,29 @@ static int old_deviceless(struct net *net, void __user *data)
return -EOPNOTSUPP;
}
-int br_ioctl_stub(struct net *net, struct net_bridge *br, unsigned int cmd,
- struct ifreq *ifr, void __user *uarg)
+int br_ioctl_stub(struct net *net, unsigned int cmd, void __user *uarg)
{
int ret = -EOPNOTSUPP;
+ struct ifreq ifr;
+
+ switch (cmd) {
+ case SIOCBRADDIF:
+ case SIOCBRDELIF: {
+ void __user *data;
+ char *colon;
+
+ if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
+ return -EPERM;
+
+ if (get_user_ifreq(&ifr, &data, uarg))
+ return -EFAULT;
+
+ ifr.ifr_name[IFNAMSIZ - 1] = 0;
+ colon = strchr(ifr.ifr_name, ':');
+ if (colon)
+ *colon = 0;
+ }
+ }
rtnl_lock();
@@ -430,9 +449,23 @@ int br_ioctl_stub(struct net *net, struct net_bridge *br, unsigned int cmd,
break;
case SIOCBRADDIF:
case SIOCBRDELIF:
- ret = add_del_if(br, ifr->ifr_ifindex, cmd == SIOCBRADDIF);
+ {
+ struct net_device *dev;
+
+ dev = __dev_get_by_name(net, ifr.ifr_name);
+ if (!dev || !netif_device_present(dev)) {
+ ret = -ENODEV;
+ break;
+ }
+ if (!netif_is_bridge_master(dev)) {
+ ret = -EOPNOTSUPP;
+ break;
+ }
+
+ ret = add_del_if(netdev_priv(dev), ifr.ifr_ifindex, cmd == SIOCBRADDIF);
break;
}
+ }
rtnl_unlock();
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index 1054b8a88edc..d5b3c5936a79 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -949,8 +949,7 @@ br_port_get_check_rtnl(const struct net_device *dev)
/* br_ioctl.c */
int br_dev_siocdevprivate(struct net_device *dev, struct ifreq *rq,
void __user *data, int cmd);
-int br_ioctl_stub(struct net *net, struct net_bridge *br, unsigned int cmd,
- struct ifreq *ifr, void __user *uarg);
+int br_ioctl_stub(struct net *net, unsigned int cmd, void __user *uarg);
/* br_multicast.c */
#ifdef CONFIG_BRIDGE_IGMP_SNOOPING
diff --git a/net/core/dev_ioctl.c b/net/core/dev_ioctl.c
index 4c2098ac9d72..57f79f8e8466 100644
--- a/net/core/dev_ioctl.c
+++ b/net/core/dev_ioctl.c
@@ -551,7 +551,6 @@ static int dev_ifsioc(struct net *net, struct ifreq *ifr, void __user *data,
int err;
struct net_device *dev = __dev_get_by_name(net, ifr->ifr_name);
const struct net_device_ops *ops;
- netdevice_tracker dev_tracker;
if (!dev)
return -ENODEV;
@@ -614,22 +613,6 @@ static int dev_ifsioc(struct net *net, struct ifreq *ifr, void __user *data,
case SIOCWANDEV:
return dev_siocwandev(dev, &ifr->ifr_settings);
- case SIOCBRADDIF:
- case SIOCBRDELIF:
- if (!netif_device_present(dev))
- return -ENODEV;
- if (!netif_is_bridge_master(dev))
- return -EOPNOTSUPP;
-
- netdev_hold(dev, &dev_tracker, GFP_KERNEL);
- rtnl_net_unlock(net);
-
- err = br_ioctl_call(net, netdev_priv(dev), cmd, ifr, NULL);
-
- netdev_put(dev, &dev_tracker);
- rtnl_net_lock(net);
- return err;
-
case SIOCDEVPRIVATE ... SIOCDEVPRIVATE + 15:
return dev_siocdevprivate(dev, ifr, data, cmd);
@@ -812,8 +795,6 @@ int dev_ioctl(struct net *net, unsigned int cmd, struct ifreq *ifr,
case SIOCBONDRELEASE:
case SIOCBONDSETHWADDR:
case SIOCBONDCHANGEACTIVE:
- case SIOCBRADDIF:
- case SIOCBRDELIF:
case SIOCSHWTSTAMP:
if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
return -EPERM;
diff --git a/net/socket.c b/net/socket.c
index 28bae5a94234..38227d00d198 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1145,12 +1145,10 @@ static ssize_t sock_write_iter(struct kiocb *iocb, struct iov_iter *from)
*/
static DEFINE_MUTEX(br_ioctl_mutex);
-static int (*br_ioctl_hook)(struct net *net, struct net_bridge *br,
- unsigned int cmd, struct ifreq *ifr,
+static int (*br_ioctl_hook)(struct net *net, unsigned int cmd,
void __user *uarg);
-void brioctl_set(int (*hook)(struct net *net, struct net_bridge *br,
- unsigned int cmd, struct ifreq *ifr,
+void brioctl_set(int (*hook)(struct net *net, unsigned int cmd,
void __user *uarg))
{
mutex_lock(&br_ioctl_mutex);
@@ -1159,8 +1157,7 @@ void brioctl_set(int (*hook)(struct net *net, struct net_bridge *br,
}
EXPORT_SYMBOL(brioctl_set);
-int br_ioctl_call(struct net *net, struct net_bridge *br, unsigned int cmd,
- struct ifreq *ifr, void __user *uarg)
+int br_ioctl_call(struct net *net, unsigned int cmd, void __user *uarg)
{
int err = -ENOPKG;
@@ -1169,7 +1166,7 @@ int br_ioctl_call(struct net *net, struct net_bridge *br, unsigned int cmd,
mutex_lock(&br_ioctl_mutex);
if (br_ioctl_hook)
- err = br_ioctl_hook(net, br, cmd, ifr, uarg);
+ err = br_ioctl_hook(net, cmd, uarg);
mutex_unlock(&br_ioctl_mutex);
return err;
@@ -1269,7 +1266,9 @@ static long sock_ioctl(struct file *file, unsigned cmd, unsigned long arg)
case SIOCSIFBR:
case SIOCBRADDBR:
case SIOCBRDELBR:
- err = br_ioctl_call(net, NULL, cmd, NULL, argp);
+ case SIOCBRADDIF:
+ case SIOCBRDELIF:
+ err = br_ioctl_call(net, cmd, argp);
break;
case SIOCGIFVLAN:
case SIOCSIFVLAN:
@@ -3429,6 +3428,8 @@ static int compat_sock_ioctl_trans(struct file *file, struct socket *sock,
case SIOCGPGRP:
case SIOCBRADDBR:
case SIOCBRDELBR:
+ case SIOCBRADDIF:
+ case SIOCBRDELIF:
case SIOCGIFVLAN:
case SIOCSIFVLAN:
case SIOCGSKNS:
@@ -3468,8 +3469,6 @@ static int compat_sock_ioctl_trans(struct file *file, struct socket *sock,
case SIOCGIFPFLAGS:
case SIOCGIFTXQLEN:
case SIOCSIFTXQLEN:
- case SIOCBRADDIF:
- case SIOCBRDELIF:
case SIOCGIFNAME:
case SIOCSIFNAME:
case SIOCGMIIPHY:
--
2.48.1
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