linux-stable.git/net/core/dev.c, branch v7.1.5

net: serialize netif_running() check in enqueue_to_backlog()

2026-07-24T14:19:57+00:00

[ Upstream commit 46762cefe7f4e5bffc1eb467810a7bbb02e461d7 ]

Syzbot reported a KASAN slab-use-after-free in fib_rules_lookup().

The root cause is a race condition where packets can escape the backlog
flushing during device unregistration (e.g., during netns exit).

Commit e9e4dd3267d0 ("net: do not process device backlog during unregistration")
introduced a lockless netif_running() check in enqueue_to_backlog() to
prevent queuing packets to an unregistering device.

However, this creates a TOCTOU race window.

A lockless transmitter (like veth_xmit) can pass
the check before dev_close() clears IFF_UP. If the transmitter is then
delayed, flush_all_backlogs() can run and finish before the transmitter
grabs the backlog lock and queues the packet. The packet then escapes
the flush and triggers UAF later when processed.

Fix this by moving the netif_running() check inside the backlog lock.
This serializes the check with the flush work (which also grabs the lock).
We then either queue the packet before the flush runs (so it gets flushed),
or check netif_running() after the flush/close completes (so it gets dropped).

Fixes: e9e4dd3267d0 ("net: do not process device backlog during unregistration")
Reported-by: syzbot+965506b59a2de0b6905c@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6a315824.b0403584.28d0ff.0000.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet 
Cc: Julian Anastasov 
Reviewed-by: Kuniyuki Iwashima 
Link: https://patch.msgid.link/20260616141317.407791-1-edumazet@google.com
Signed-off-by: Jakub Kicinski 
Signed-off-by: Sasha Levin

net: watchdog: fix refcount tracking races

2026-07-24T14:19:52+00:00

[ Upstream commit 8eed5519e496b7a07f441a0f579cb228a33189f7 ]

Blamed commit converted the untracked dev_hold()/dev_put() calls
in the watchdog code to use the tracked dev_hold_track()/dev_put_track()
(which were later renamed/interfaced to netdev_hold() and netdev_put()).

By introducing dev->watchdog_dev_tracker to store the
reference tracking information without adding synchronization
between netdev_watchdog_up() and dev_watchdog(), it enabled the
race condition where this pointer could be overwritten or freed
concurrently, leading to the list corruption crash syzbot reported:

list_del corruption, ffff888114a18c00->next is NULL
 kernel BUG at lib/list_debug.c:52 !
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 1 UID: 0 PID: 91 Comm: kworker/u8:5 Not tainted syzkaller #0 PREEMPT(lazy)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: events_unbound linkwatch_event
 RIP: 0010:__list_del_entry_valid_or_report.cold+0x22/0x2a lib/list_debug.c:52
Call Trace:
 
  __list_del_entry_valid include/linux/list.h:132 [inline]
  __list_del_entry include/linux/list.h:246 [inline]
  list_move_tail include/linux/list.h:341 [inline]
  ref_tracker_free+0x1a7/0x6c0 lib/ref_tracker.c:329
  netdev_tracker_free include/linux/netdevice.h:4491 [inline]
  netdev_put include/linux/netdevice.h:4508 [inline]
  netdev_put include/linux/netdevice.h:4504 [inline]
  netdev_watchdog_down net/sched/sch_generic.c:600 [inline]
  dev_deactivate_many+0x28c/0xfe0 net/sched/sch_generic.c:1363
  dev_deactivate+0x109/0x1d0 net/sched/sch_generic.c:1397
  linkwatch_do_dev net/core/link_watch.c:184 [inline]
  linkwatch_do_dev+0xd3/0x120 net/core/link_watch.c:166
  __linkwatch_run_queue+0x3a5/0x810 net/core/link_watch.c:240
  linkwatch_event+0x8f/0xc0 net/core/link_watch.c:314
  process_one_work+0xa0e/0x1980 kernel/workqueue.c:3314
  process_scheduled_works kernel/workqueue.c:3397 [inline]
  worker_thread+0x5ef/0xe50 kernel/workqueue.c:3478
  kthread+0x370/0x450 kernel/kthread.c:436
  ret_from_fork+0x69a/0xc80 arch/x86/kernel/process.c:158
  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

This patch has three coordinated parts:

1) Add dev->watchdog_lock and dev->watchdog_ref_held to serialize watchdog operations.

2) Remove netdev_watchdog_up() call from netif_carrier_on():
   This ensures netdev_watchdog_up() is only called from process/BH context
   (via linkwatch workqueue dev_activate()), allowing us to use
   spin_lock_bh() for synchronization.

3) Synchronize watchdog up and watchdog timer:
   Protect netdev_watchdog_up() with tx_global_lock and watchdog_lock.
   Only allocate a new tracker in netdev_watchdog_up() if one is
   not already present.
   In dev_watchdog(), ensure we don't release the tracker if the
   timer was rescheduled either by dev_watchdog() itself or concurrently
   by netdev_watchdog_up().

Fixes: f12bf6f3f942 ("net: watchdog: add net device refcount tracker")
Reported-by: syzbot+381d82bbf0253710b35d@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6a26b751.c25708ab.1b19ef.0013.GAE@google.com/T/#u
Tested-by: syzbot+3479efbc2821cb2a79f2@syzkaller.appspotmail.com
Signed-off-by: Eric Dumazet 
Link: https://patch.msgid.link/20260611152737.2580480-1-edumazet@google.com
Signed-off-by: Jakub Kicinski 
Signed-off-by: Sasha Levin

net: napi: Avoid gro timer misfiring at end of busypoll

2026-05-08T22:02:32+00:00

When in irq deferral mode (defer-hard-irqs > 0), a short enough
gro-flush timeout can trigger before NAPI_STATE_SCHED is cleared if the
last poll in busy_poll_stop() takes too long. This can have the effect
of leaving the queue stuck with interrupts disabled and no timer armed
which results in a tx timeout if there is no subsequent busypoll cycle.

To prevent this, defer the gro-flush timer arm after the last poll.

Fixes: 7fd3253a7de6 ("net: Introduce preferred busy-polling")
Co-developed-by: Martin Karsten 
Signed-off-by: Martin Karsten 
Signed-off-by: Dragos Tatulea 
Reviewed-by: Tariq Toukan 
Reviewed-by: Cosmin Ratiu 
Reviewed-by: Joe Damato 
Link: https://patch.msgid.link/20260506090808.820559-2-dtatulea@nvidia.com
Signed-off-by: Jakub Kicinski

net: prevent possible UAF in rtnl_prop_list_size()

2026-05-05T02:24:27+00:00

I was mistaken by synchronize_rcu() [1] call in netdev_name_node_alt_destroy(),
giving a false sense of RCU safety at delete times.

We have to use list_del_rcu() to not confuse potential readers
in rtnl_prop_list_size().

[1] This synchronize_rcu() call was later removed in commit 723de3ebef03
("net: free altname using an RCU callback").

Fixes: 9f30831390ed ("net: add rcu safety to rtnl_prop_list_size()")
Signed-off-by: Eric Dumazet 
Link: https://patch.msgid.link/20260502124102.499204-1-edumazet@google.com
Signed-off-by: Jakub Kicinski

Merge tag 'net-deletions' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next

2026-04-24T16:41:58+00:00

Pull networking deletions from Jakub Kicinski:
 "Delete some obsolete networking code

  Old code like amateur radio and NFC have long been a burden to core
  networking developers. syzbot loves to find bugs in BKL-era code, and
  noobs try to fix them.

  If we want to have a fighting chance of surviving the LLM-pocalypse
  this code needs to find a dedicated owner or get deleted. We've talked
  about these deletions multiple times in the past and every time
  someone wanted the code to stay. It is never very clear to me how many
  of those people actually use the code vs are just nostalgic to see it
  go. Amateur radio did have occasional users (or so I think) but most
  users switched to user space implementations since its all super slow
  stuff. Nobody stepped up to maintain the kernel code.

  We were lucky enough to find someone who wants to help with NFC so
  we're giving that a chance. Let's try to put the rest of this code
  behind us"

* tag 'net-deletions' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next:
  drivers: net: 8390: wd80x3: Remove this driver
  drivers: net: 8390: ultra: Remove this driver
  drivers: net: 8390: AX88190: Remove this driver
  drivers: net: fujitsu: fmvj18x: Remove this driver
  drivers: net: smsc: smc91c92: Remove this driver
  drivers: net: smsc: smc9194: Remove this driver
  drivers: net: amd: nmclan: Remove this driver
  drivers: net: amd: lance: Remove this driver
  drivers: net: 3com: 3c589: Remove this driver
  drivers: net: 3com: 3c574: Remove this driver
  drivers: net: 3com: 3c515: Remove this driver
  drivers: net: 3com: 3c509: Remove this driver
  net: packetengines: remove obsolete yellowfin driver and vendor dir
  net: packetengines: remove obsolete hamachi driver
  net: remove unused ATM protocols and legacy ATM device drivers
  net: remove ax25 and amateur radio (hamradio) subsystem
  net: remove ISDN subsystem and Bluetooth CMTP
  caif: remove CAIF NETWORK LAYER

net: remove unused ATM protocols and legacy ATM device drivers

2026-04-23T19:21:14+00:00

Remove the ATM protocol modules and PCI/SBUS ATM device drivers
that are no longer in active use.

The ATM core protocol stack, PPPoATM, BR2684, and USB DSL modem
drivers (drivers/usb/atm/) are retained in-tree to maintain PPP
over ATM (PPPoA) and PPPoE-over-BR2684 support for DSL connections.
The Solos ADSL2+ PCI driver is also retained.

Removed ATM protocol modules:
 - net/atm/clip.c - Classical IP over ATM (RFC 2225)
 - net/atm/lec.c - LAN Emulation Client (LANE)
 - net/atm/mpc.c, mpoa_caches.c, mpoa_proc.c - Multi-Protocol Over ATM

Removed PCI/SBUS ATM device drivers (drivers/atm/):
 - adummy, atmtcp - software/testing ATM devices
 - eni - Efficient Networks ENI155P (OC-3, ~1995)
 - fore200e - FORE Systems 200E PCI/SBUS (OC-3, ~1999)
 - he - ForeRunner HE (OC-3/OC-12, ~2000)
 - idt77105 - IDT 77105 25 Mbps ATM PHY
 - idt77252 - IDT 77252 NICStAR II (OC-3, ~2000)
 - iphase - Interphase ATM PCI (OC-3/DS3/E3)
 - lanai - Efficient Networks Speedstream 3010
 - nicstar - IDT 77201 NICStAR (155/25 Mbps, ~1999)
 - suni - PMC S/UNI SONET PHY library

Also clean up references in:
 - net/bridge/ - remove ATM LANE hook (br_fdb_test_addr_hook,
   br_fdb_test_addr)
 - net/core/dev.c - remove br_fdb_test_addr_hook export
 - defconfig files - remove ATM driver config options

The removed code is moved to an out-of-tree module package (mod-orphan).

Acked-by: Andy Shevchenko 
Reviewed-by: Simon Horman 
Reviewed-by: Nikolay Aleksandrov 
Link: https://patch.msgid.link/20260422041846.2035118-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski

net: warn ops-locked drivers still using ndo_set_rx_mode

2026-04-21T10:50:25+00:00

Now that all in-tree ops-locked drivers have been converted to
ndo_set_rx_mode_async, add a warning in register_netdevice to catch
any remaining or newly added drivers that use ndo_set_rx_mode with
ops locking. This ensures future driver authors are guided toward
the async path.

Also route ops-locked devices through netdev_rx_mode_work even if they
lack rx_mode NDOs, to ensure netdev_ops_assert_locked() does not fire
on the legacy path where only RTNL is held.

Reviewed-by: Aleksandr Loktionov 
Signed-off-by: Stanislav Fomichev 
Link: https://patch.msgid.link/20260416185712.2155425-14-sdf@fomichev.me
Signed-off-by: Paolo Abeni

net: move promiscuity handling into netdev_rx_mode_work

2026-04-21T10:50:24+00:00

Move unicast promiscuity tracking into netdev_rx_mode_work so it runs
under netdev_ops_lock instead of under the addr_lock spinlock. This
is required because __dev_set_promiscuity calls dev_change_rx_flags
and __dev_notify_flags, both of which may need to sleep.

Change ASSERT_RTNL() to netdev_ops_assert_locked() in
__dev_set_promiscuity, netif_set_allmulti and __dev_change_flags
since these are now called from the work queue under the ops lock.

Link: https://lore.kernel.org/netdev/20260214033859.43857-1-jiayuan.chen@linux.dev/
Fixes: 78cd408356fe ("net: add missing instance lock to dev_set_promiscuity")
Reported-by: syzbot+2b3391f44313b3983e91@syzkaller.appspotmail.com
Reviewed-by: Aleksandr Loktionov 
Signed-off-by: Stanislav Fomichev 
Link: https://patch.msgid.link/20260416185712.2155425-5-sdf@fomichev.me
Signed-off-by: Paolo Abeni

net: cache snapshot entries for ndo_set_rx_mode_async

2026-04-21T10:50:13+00:00

Add a per-device netdev_hw_addr_list cache (rx_mode_addr_cache) that
allows __hw_addr_list_snapshot() and __hw_addr_list_reconcile() to
reuse previously allocated entries instead of hitting GFP_ATOMIC on
every snapshot cycle.

snapshot pops entries from the cache when available, falling back to
__hw_addr_create(). reconcile splices both snapshot lists back into
the cache via __hw_addr_splice(). The cache is flushed in
free_netdev().

Signed-off-by: Stanislav Fomichev 
Link: https://patch.msgid.link/20260416185712.2155425-4-sdf@fomichev.me
Signed-off-by: Paolo Abeni

net: introduce ndo_set_rx_mode_async and netdev_rx_mode_work

2026-04-21T10:50:03+00:00

Add ndo_set_rx_mode_async callback that drivers can implement instead
of the legacy ndo_set_rx_mode. The legacy callback runs under the
netif_addr_lock spinlock with BHs disabled, preventing drivers from
sleeping. The async variant runs from a work queue with rtnl_lock and
netdev_lock_ops held, in fully sleepable context.

When __dev_set_rx_mode() sees ndo_set_rx_mode_async, it schedules
netdev_rx_mode_work instead of calling the driver inline. The work
function takes two snapshots of each address list (uc/mc) under
the addr_lock, then drops the lock and calls the driver with the
work copies. After the driver returns, it reconciles the snapshots
back to the real lists under the lock.

Add netif_rx_mode_sync() to opportunistically execute the pending
workqueue update inline, so that rx mode changes are committed
before returning to userspace:
  - dev_change_flags (SIOCSIFFLAGS / RTM_NEWLINK)
  - dev_set_promiscuity
  - dev_set_allmulti
  - dev_ifsioc SIOCADDMULTI / SIOCDELMULTI
  - do_setlink (RTM_SETLINK)

Note that some deep hierarchies still do skip the lower updates via:
  - dev_uc_sync
  - dev_mc_sync

If we do end up hitting user-visible issues, we can add more calls to
netif_rx_mode_sync in specific places. But hopefully we should not,
the actual user-visible lists are still synced, it's that just HW state
that might be lagging.

Signed-off-by: Stanislav Fomichev 
Link: https://patch.msgid.link/20260416185712.2155425-3-sdf@fomichev.me
Signed-off-by: Paolo Abeni