kernel/linux.git/net/core/netpoll.c, branch v6.6.132

net: netpoll: ensure skb_pool list is always initialized

2025-11-24T09:30:13+00:00

commit f0d0277796db613c124206544b6dbe95b520ab6c upstream. When __netpoll_setup() is called directly, instead of through netpoll_setup(), the np->skb_pool list head isn't initialized. If skb_pool_flush() is later called, then we hit a NULL pointer in skb_queue_purge_reason(). This can be seen with this repro, when CONFIG_NETCONSOLE is enabled as a module: ip tuntap add mode tap tap0 ip link add name br0 type bridge ip link set dev tap0 master br0 modprobe netconsole netconsole=4444@10.0.0.1/br0,9353@10.0.0.2/ rmmod netconsole The backtrace is: BUG: kernel NULL pointer dereference, address: 0000000000000008 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page ... ... ... Call Trace: __netpoll_free+0xa5/0xf0 br_netpoll_cleanup+0x43/0x50 [bridge] do_netpoll_cleanup+0x43/0xc0 netconsole_netdev_event+0x1e3/0x300 [netconsole] unregister_netdevice_notifier+0xd9/0x150 cleanup_module+0x45/0x920 [netconsole] __se_sys_delete_module+0x205/0x290 do_syscall_64+0x70/0x150 entry_SYSCALL_64_after_hwframe+0x76/0x7e Move the skb_pool list setup and initial skb fill into __netpoll_setup(). Fixes: 221a9c1df790 ("net: netpoll: Individualize the skb pool") Signed-off-by: John Sperbeck Reviewed-by: Breno Leitao Link: https://patch.msgid.link/20250114011354.2096812-1-jsperbeck@google.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman

net: netpoll: fix incorrect refcount handling causing incorrect cleanup

2025-11-24T09:30:11+00:00

[ Upstream commit 49c8d2c1f94cc2f4d1a108530d7ba52614b874c2 ] commit efa95b01da18 ("netpoll: fix use after free") incorrectly ignored the refcount and prematurely set dev->npinfo to NULL during netpoll cleanup, leading to improper behavior and memory leaks. Scenario causing lack of proper cleanup: 1) A netpoll is associated with a NIC (e.g., eth0) and netdev->npinfo is allocated, and refcnt = 1 - Keep in mind that npinfo is shared among all netpoll instances. In this case, there is just one. 2) Another netpoll is also associated with the same NIC and npinfo->refcnt += 1. - Now dev->npinfo->refcnt = 2; - There is just one npinfo associated to the netdev. 3) When the first netpolls goes to clean up: - The first cleanup succeeds and clears np->dev->npinfo, ignoring refcnt. - It basically calls `RCU_INIT_POINTER(np->dev->npinfo, NULL);` - Set dev->npinfo = NULL, without proper cleanup - No ->ndo_netpoll_cleanup() is either called 4) Now the second target tries to clean up - The second cleanup fails because np->dev->npinfo is already NULL. * In this case, ops->ndo_netpoll_cleanup() was never called, and the skb pool is not cleaned as well (for the second netpoll instance) - This leaks npinfo and skbpool skbs, which is clearly reported by kmemleak. Revert commit efa95b01da18 ("netpoll: fix use after free") and adds clarifying comments emphasizing that npinfo cleanup should only happen once the refcount reaches zero, ensuring stable and correct netpoll behavior. Cc: # 3.17.x Cc: Jay Vosburgh Fixes: efa95b01da18 ("netpoll: fix use after free") Signed-off-by: Breno Leitao Reviewed-by: Simon Horman Link: https://patch.msgid.link/20251107-netconsole_torture-v10-1-749227b55f63@debian.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

net: netpoll: flush skb pool during cleanup

2025-11-24T09:30:11+00:00

[ Upstream commit 6c59f16f1770481a6ee684720ec55b1e38b3a4b2 ] The netpoll subsystem maintains a pool of 32 pre-allocated SKBs per instance, but these SKBs are not freed when the netpoll user is brought down. This leads to memory waste as these buffers remain allocated but unused. Add skb_pool_flush() to properly clean up these SKBs when netconsole is terminated, improving memory efficiency. Signed-off-by: Breno Leitao Link: https://patch.msgid.link/20241114-skb_buffers_v2-v3-2-9be9f52a8b69@debian.org Signed-off-by: Jakub Kicinski Stable-dep-of: 49c8d2c1f94c ("net: netpoll: fix incorrect refcount handling causing incorrect cleanup") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

net: netpoll: Individualize the skb pool

2025-11-24T09:30:10+00:00

[ Upstream commit 221a9c1df790fa711d65daf5ba05d0addc279153 ] The current implementation of the netpoll system uses a global skb pool, which can lead to inefficient memory usage and waste when targets are disabled or no longer in use. This can result in a significant amount of memory being unnecessarily allocated and retained, potentially causing performance issues and limiting the availability of resources for other system components. Modify the netpoll system to assign a skb pool to each target instead of using a global one. This approach allows for more fine-grained control over memory allocation and deallocation, ensuring that resources are only allocated and retained as needed. Signed-off-by: Breno Leitao Link: https://patch.msgid.link/20241114-skb_buffers_v2-v3-1-9be9f52a8b69@debian.org Signed-off-by: Jakub Kicinski Stable-dep-of: 49c8d2c1f94c ("net: netpoll: fix incorrect refcount handling causing incorrect cleanup") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

netpoll: remove netpoll_srcu

2025-11-24T09:30:10+00:00

[ Upstream commit 9a95eedc81deb86af1ac56f2c2bfe8306b27b82a ] netpoll_srcu is currently used from netpoll_poll_disable() and __netpoll_cleanup() Both functions run under RTNL, using netpoll_srcu adds confusion and no additional protection. Moreover the synchronize_srcu() call in __netpoll_cleanup() is performed before clearing np->dev->npinfo, which violates RCU rules. After this patch, netpoll_poll_disable() and netpoll_poll_enable() simply use rtnl_dereference(). This saves a big chunk of memory (more than 192KB on platforms with 512 cpus) Signed-off-by: Eric Dumazet Reviewed-by: Breno Leitao Link: https://patch.msgid.link/20240905084909.2082486-1-edumazet@google.com Signed-off-by: Jakub Kicinski Stable-dep-of: 49c8d2c1f94c ("net: netpoll: fix incorrect refcount handling causing incorrect cleanup") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

netpoll: prevent hanging NAPI when netcons gets enabled

2025-08-15T10:09:02+00:00

[ Upstream commit 2da4def0f487f24bbb0cece3bb2bcdcb918a0b72 ] Paolo spotted hangs in NIPA running driver tests against virtio. The tests hang in virtnet_close() -> virtnet_napi_tx_disable(). The problem is only reproducible if running multiple of our tests in sequence (I used TEST_PROGS="xdp.py ping.py netcons_basic.sh \ netpoll_basic.py stats.py"). Initial suspicion was that this is a simple case of double-disable of NAPI, but instrumenting the code reveals: Deadlocked on NAPI ffff888007cd82c0 (virtnet_poll_tx): state: 0x37, disabled: false, owner: 0, listed: false, weight: 64 The NAPI was not in fact disabled, owner is 0 (rather than -1), so the NAPI "thinks" it's scheduled for CPU 0 but it's not listed (!list_empty(&n->poll_list) => false). It seems odd that normal NAPI processing would wedge itself like this. Better suspicion is that netpoll gets enabled while NAPI is polling, and also grabs the NAPI instance. This confuses napi_complete_done(): [netpoll] [normal NAPI] napi_poll() have = netpoll_poll_lock() rcu_access_pointer(dev->npinfo) return NULL # no netpoll __napi_poll() ->poll(->weight) poll_napi() cmpxchg(->poll_owner, -1, cpu) poll_one_napi() set_bit(NAPI_STATE_NPSVC, ->state) napi_complete_done() if (NAPIF_STATE_NPSVC) return false # exit without clearing SCHED This feels very unlikely, but perhaps virtio has some interactions with the hypervisor in the NAPI ->poll that makes the race window larger? Best I could to to prove the theory was to add and trigger this warning in napi_poll (just before netpoll_poll_unlock()): WARN_ONCE(!have && rcu_access_pointer(n->dev->npinfo) && napi_is_scheduled(n) && list_empty(&n->poll_list), "NAPI race with netpoll %px", n); If this warning hits the next virtio_close() will hang. This patch survived 30 test iterations without a hang (without it the longest clean run was around 10). Credit for triggering this goes to Breno's recent netconsole tests. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: Paolo Abeni Link: https://lore.kernel.org/c5a93ed1-9abe-4880-a3bb-8d1678018b1d@redhat.com Acked-by: Jason Wang Reviewed-by: Xuan Zhuo Link: https://patch.msgid.link/20250726010846.1105875-1-kuba@kernel.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin

netpoll: hold rcu read lock in __netpoll_send_skb()

2025-03-22T19:50:38+00:00

[ Upstream commit 505ead7ab77f289f12d8a68ac83da068e4d4408b ] The function __netpoll_send_skb() is being invoked without holding the RCU read lock. This oversight triggers a warning message when CONFIG_PROVE_RCU_LIST is enabled: net/core/netpoll.c:330 suspicious rcu_dereference_check() usage! netpoll_send_skb netpoll_send_udp write_ext_msg console_flush_all console_unlock vprintk_emit To prevent npinfo from disappearing unexpectedly, ensure that __netpoll_send_skb() is protected with the RCU read lock. Fixes: 2899656b494dcd1 ("netpoll: take rcu_read_lock_bh() in netpoll_send_skb_on_dev()") Signed-off-by: Breno Leitao Reviewed-by: Simon Horman Link: https://patch.msgid.link/20250306-netpoll_rcu_v2-v2-1-bc4f5c51742a@debian.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin

netpoll: Use rcu_access_pointer() in __netpoll_setup

2024-12-14T19:00:10+00:00

[ Upstream commit c69c5e10adb903ae2438d4f9c16eccf43d1fcbc1 ] The ndev->npinfo pointer in __netpoll_setup() is RCU-protected but is being accessed directly for a NULL check. While no RCU read lock is held in this context, we should still use proper RCU primitives for consistency and correctness. Replace the direct NULL check with rcu_access_pointer(), which is the appropriate primitive when only checking for NULL without dereferencing the pointer. This function provides the necessary ordering guarantees without requiring RCU read-side protection. Reviewed-by: Michal Kubiak Signed-off-by: Breno Leitao Link: https://patch.msgid.link/20241118-netpoll_rcu-v1-1-a1888dcb4a02@debian.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin

netpoll: Ensure clean state on setup failures

2024-10-10T09:57:26+00:00

[ Upstream commit ae5a0456e0b4cfd7e61619e55251ffdf1bc7adfb ] Modify netpoll_setup() and __netpoll_setup() to ensure that the netpoll structure (np) is left in a clean state if setup fails for any reason. This prevents carrying over misconfigured fields in case of partial setup success. Key changes: - np->dev is now set only after successful setup, ensuring it's always NULL if netpoll is not configured or if netpoll_setup() fails. - np->local_ip is zeroed if netpoll setup doesn't complete successfully. - Added DEBUG_NET_WARN_ON_ONCE() checks to catch unexpected states. - Reordered some operations in __netpoll_setup() for better logical flow. These changes improve the reliability of netpoll configuration, since it assures that the structure is fully initialized or totally unset. Suggested-by: Paolo Abeni Signed-off-by: Breno Leitao Link: https://patch.msgid.link/20240822111051.179850-2-leitao@debian.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin

netpoll: Fix race condition in netpoll_owner_active

2024-06-27T11:49:02+00:00

[ Upstream commit c2e6a872bde9912f1a7579639c5ca3adf1003916 ] KCSAN detected a race condition in netpoll: BUG: KCSAN: data-race in net_rx_action / netpoll_send_skb write (marked) to 0xffff8881164168b0 of 4 bytes by interrupt on cpu 10: net_rx_action (./include/linux/netpoll.h:90 net/core/dev.c:6712 net/core/dev.c:6822) read to 0xffff8881164168b0 of 4 bytes by task 1 on cpu 2: netpoll_send_skb (net/core/netpoll.c:319 net/core/netpoll.c:345 net/core/netpoll.c:393) netpoll_send_udp (net/core/netpoll.c:?) value changed: 0x0000000a -> 0xffffffff This happens because netpoll_owner_active() needs to check if the current CPU is the owner of the lock, touching napi->poll_owner non atomically. The ->poll_owner field contains the current CPU holding the lock. Use an atomic read to check if the poll owner is the current CPU. Signed-off-by: Breno Leitao Link: https://lore.kernel.org/r/20240429100437.3487432-1-leitao@debian.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin