From ed3ba9b6e280e14cc3148c1b226ba453f02fa76c Mon Sep 17 00:00:00 2001 From: Kuniyuki Iwashima Date: Sun, 16 Mar 2025 12:28:37 -0700 Subject: 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 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 |- 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@ffff8880662d8608 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 Reported-by: yan kang Reported-by: yue sun Closes: https://lore.kernel.org/netdev/SY8P300MB0421225D54EB92762AE8F0F2A1D32@SY8P300MB0421.AUSP300.PROD.OUTLOOK.COM/ Signed-off-by: Kuniyuki Iwashima Acked-by: Stanislav Fomichev Reviewed-by: Ido Schimmel Acked-by: Nikolay Aleksandrov Link: https://patch.msgid.link/20250316192851.19781-1-kuniyu@amazon.com Signed-off-by: Paolo Abeni --- net/socket.c | 19 +++++++++---------- 1 file changed, 9 insertions(+), 10 deletions(-) (limited to 'net/socket.c') 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: -- cgit