[PATCH net-next] net: destroy dev->lock later in free_netdev()

[PATCH net-next] net: destroy dev->lock later in free_netdev()

[Eric Dumazet]

syzbot complained that free_netdev() was calling netif_napi_del()
after dev->lock mutex has been destroyed.

This fires a warning for CONFIG_DEBUG_MUTEXES=y builds.

Move mutex_destroy(&dev->lock) near the end of free_netdev().

[1]
DEBUG_LOCKS_WARN_ON(lock->magic != lock)
 WARNING: CPU: 0 PID: 5971 at kernel/locking/mutex.c:564 __mutex_lock_common kernel/locking/mutex.c:564 [inline]
 WARNING: CPU: 0 PID: 5971 at kernel/locking/mutex.c:564 __mutex_lock+0xdac/0xee0 kernel/locking/mutex.c:735
Modules linked in:
CPU: 0 UID: 0 PID: 5971 Comm: syz-executor Not tainted 6.13.0-rc7-syzkaller-01131-g8d20dcda404d #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
 RIP: 0010:__mutex_lock_common kernel/locking/mutex.c:564 [inline]
 RIP: 0010:__mutex_lock+0xdac/0xee0 kernel/locking/mutex.c:735
Code: 0f b6 04 38 84 c0 0f 85 1a 01 00 00 83 3d 6f 40 4c 04 00 75 19 90 48 c7 c7 60 84 0a 8c 48 c7 c6 00 85 0a 8c e8 f5 dc 91 f5 90 <0f> 0b 90 90 90 e9 c7 f3 ff ff 90 0f 0b 90 e9 29 f8 ff ff 90 0f 0b
RSP: 0018:ffffc90003317580 EFLAGS: 00010246
RAX: ee0f97edaf7b7d00 RBX: ffff8880299f8cb0 RCX: ffff8880323c9e00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90003317710 R08: ffffffff81602ac2 R09: 1ffff110170c519a
R10: dffffc0000000000 R11: ffffed10170c519b R12: 0000000000000000
R13: 0000000000000000 R14: 1ffff92000662ec4 R15: dffffc0000000000
FS:  000055557a046500(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd581d46ff8 CR3: 000000006f870000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
  netdev_lock include/linux/netdevice.h:2691 [inline]
  __netif_napi_del include/linux/netdevice.h:2829 [inline]
  netif_napi_del include/linux/netdevice.h:2848 [inline]
  free_netdev+0x2d9/0x610 net/core/dev.c:11621
  netdev_run_todo+0xf21/0x10d0 net/core/dev.c:11189
  nsim_destroy+0x3c3/0x620 drivers/net/netdevsim/netdev.c:1028
  __nsim_dev_port_del+0x14b/0x1b0 drivers/net/netdevsim/dev.c:1428
  nsim_dev_port_del_all drivers/net/netdevsim/dev.c:1440 [inline]
  nsim_dev_reload_destroy+0x28a/0x490 drivers/net/netdevsim/dev.c:1661
  nsim_drv_remove+0x58/0x160 drivers/net/netdevsim/dev.c:1676
  device_remove drivers/base/dd.c:567 [inline]

Fixes: 1b23cdbd2bbc ("net: protect netdev->napi_list with netdev_lock()")
Reported-by: syzbot+85ff1051228a04613a32@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/678add43.050a0220.303755.0016.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/core/dev.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index fe5f5855593db34cb4bc31e6a637b59b9041bb73..fab4899b83f745a3c13c982775e287b1ff2f547d 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -11593,8 +11593,6 @@ void free_netdev(struct net_device *dev)
 		return;
 	}
 
-	mutex_destroy(&dev->lock);
-
 	kfree(dev->ethtool);
 	netif_free_tx_queues(dev);
 	netif_free_rx_queues(dev);
@@ -11621,6 +11619,8 @@ void free_netdev(struct net_device *dev)
 
 	netdev_free_phy_link_topology(dev);
 
+	mutex_destroy(&dev->lock);
+
 	/*  Compatibility with error handling in drivers */
 	if (dev->reg_state == NETREG_UNINITIALIZED ||
 	    dev->reg_state == NETREG_DUMMY) {
-- 
2.48.0.rc2.279.g1de40edade-goog

Re: [PATCH net-next] net: destroy dev->lock later in free_netdev()

[Jakub Kicinski]

On Fri, 17 Jan 2025 22:46:26 +0000 Eric Dumazet wrote:
> syzbot complained that free_netdev() was calling netif_napi_del()
> after dev->lock mutex has been destroyed.
> 
> This fires a warning for CONFIG_DEBUG_MUTEXES=y builds.
> 
> Move mutex_destroy(&dev->lock) near the end of free_netdev().

Reviewed-by: Jakub Kicinski <kuba@kernel.org>

Re: [PATCH net-next] net: destroy dev->lock later in free_netdev()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Fri, 17 Jan 2025 22:46:26 +0000 you wrote:
> syzbot complained that free_netdev() was calling netif_napi_del()
> after dev->lock mutex has been destroyed.
> 
> This fires a warning for CONFIG_DEBUG_MUTEXES=y builds.
> 
> Move mutex_destroy(&dev->lock) near the end of free_netdev().
> 
> [...]

Here is the summary with links:
  - [net-next] net: destroy dev->lock later in free_netdev()
    https://git.kernel.org/netdev/net-next/c/bff406bc0424

You are awesome, thank you!
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