syzbot presented an use-after-free report [0] regarding ipvlan and
linkwatch.

ipvlan does not hold a refcnt of the lower device unlike vlan and
macvlan.

If the linkwatch work is triggered for the ipvlan dev, the lower dev
might have already been freed, resulting in UAF of ipvlan->phy_dev in
ipvlan_get_iflink().

We can delay the lower dev unregistration like vlan and macvlan by
holding the lower dev's refcnt in dev->netdev_ops->ndo_init() and
releasing it in dev->priv_destructor().

Jakub pointed out calling .ndo_XXX after unregister_netdevice() has
returned is error prone and suggested [1] addressing this UAF in the
core by taking commit 750e516 ("net: avoid potential UAF in
default_operstate()") further.

Let's assume unregistering devices DOWN and use RCU protection in
default_operstate() not to race with the device unregistration.

[0]:
BUG: KASAN: slab-use-after-free in ipvlan_get_iflink+0x84/0x88 drivers/net/ipvlan/ipvlan_main.c:353
Read of size 4 at addr ffff0000d768c0e0 by task kworker/u8:35/6944

CPU: 0 UID: 0 PID: 6944 Comm: kworker/u8:35 Not tainted 6.13.0-rc2-g9bc5c9515b48 #12 4c3cb9e8b4565456f6a355f312ff91f4f29b3c47
Hardware name: linux,dummy-virt (DT)
Workqueue: events_unbound linkwatch_event
Call trace:
 show_stack+0x38/0x50 arch/arm64/kernel/stacktrace.c:484 (C)
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0xbc/0x108 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x16c/0x6f0 mm/kasan/report.c:489
 kasan_report+0xc0/0x120 mm/kasan/report.c:602
 __asan_report_load4_noabort+0x20/0x30 mm/kasan/report_generic.c:380
 ipvlan_get_iflink+0x84/0x88 drivers/net/ipvlan/ipvlan_main.c:353
 dev_get_iflink+0x7c/0xd8 net/core/dev.c:674
 default_operstate net/core/link_watch.c:45 [inline]
 rfc2863_policy+0x144/0x360 net/core/link_watch.c:72
 linkwatch_do_dev+0x60/0x228 net/core/link_watch.c:175
 __linkwatch_run_queue+0x2f4/0x5b8 net/core/link_watch.c:239
 linkwatch_event+0x64/0xa8 net/core/link_watch.c:282
 process_one_work+0x700/0x1398 kernel/workqueue.c:3229
 process_scheduled_works kernel/workqueue.c:3310 [inline]
 worker_thread+0x8c4/0xe10 kernel/workqueue.c:3391
 kthread+0x2b0/0x360 kernel/kthread.c:389
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:862

Allocated by task 9303:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x30/0x68 mm/kasan/common.c:68
 kasan_save_alloc_info+0x44/0x58 mm/kasan/generic.c:568
 poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
 __kasan_kmalloc+0x84/0xa0 mm/kasan/common.c:394
 kasan_kmalloc include/linux/kasan.h:260 [inline]
 __do_kmalloc_node mm/slub.c:4283 [inline]
 __kmalloc_node_noprof+0x2a0/0x560 mm/slub.c:4289
 __kvmalloc_node_noprof+0x9c/0x230 mm/util.c:650
 alloc_netdev_mqs+0xb4/0x1118 net/core/dev.c:11209
 rtnl_create_link+0x2b8/0xb60 net/core/rtnetlink.c:3595
 rtnl_newlink_create+0x19c/0x868 net/core/rtnetlink.c:3771
 __rtnl_newlink net/core/rtnetlink.c:3896 [inline]
 rtnl_newlink+0x122c/0x15c0 net/core/rtnetlink.c:4011
 rtnetlink_rcv_msg+0x61c/0x918 net/core/rtnetlink.c:6901
 netlink_rcv_skb+0x1dc/0x398 net/netlink/af_netlink.c:2542
 rtnetlink_rcv+0x34/0x50 net/core/rtnetlink.c:6928
 netlink_unicast_kernel net/netlink/af_netlink.c:1321 [inline]
 netlink_unicast+0x618/0x838 net/netlink/af_netlink.c:1347
 netlink_sendmsg+0x5fc/0x8b0 net/netlink/af_netlink.c:1891
 sock_sendmsg_nosec net/socket.c:711 [inline]
 __sock_sendmsg net/socket.c:726 [inline]
 __sys_sendto+0x2ec/0x438 net/socket.c:2197
 __do_sys_sendto net/socket.c:2204 [inline]
 __se_sys_sendto net/socket.c:2200 [inline]
 __arm64_sys_sendto+0xe4/0x110 net/socket.c:2200
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x90/0x278 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0x13c/0x250 arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x54/0x70 arch/arm64/kernel/syscall.c:151
 el0_svc+0x4c/0xa8 arch/arm64/kernel/entry-common.c:744
 el0t_64_sync_handler+0x78/0x108 arch/arm64/kernel/entry-common.c:762
 el0t_64_sync+0x198/0x1a0 arch/arm64/kernel/entry.S:600

Freed by task 10200:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x30/0x68 mm/kasan/common.c:68
 kasan_save_free_info+0x58/0x70 mm/kasan/generic.c:582
 poison_slab_object mm/kasan/common.c:247 [inline]
 __kasan_slab_free+0x48/0x68 mm/kasan/common.c:264
 kasan_slab_free include/linux/kasan.h:233 [inline]
 slab_free_hook mm/slub.c:2338 [inline]
 slab_free mm/slub.c:4598 [inline]
 kfree+0x140/0x420 mm/slub.c:4746
 kvfree+0x4c/0x68 mm/util.c:693
 netdev_release+0x94/0xc8 net/core/net-sysfs.c:2034
 device_release+0x98/0x1c0
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x2b0/0x438 lib/kobject.c:737
 netdev_run_todo+0xdd8/0xf48 net/core/dev.c:10924
 rtnl_unlock net/core/rtnetlink.c:152 [inline]
 rtnl_net_unlock net/core/rtnetlink.c:209 [inline]
 rtnl_dellink+0x484/0x680 net/core/rtnetlink.c:3526
 rtnetlink_rcv_msg+0x61c/0x918 net/core/rtnetlink.c:6901
 netlink_rcv_skb+0x1dc/0x398 net/netlink/af_netlink.c:2542
 rtnetlink_rcv+0x34/0x50 net/core/rtnetlink.c:6928
 netlink_unicast_kernel net/netlink/af_netlink.c:1321 [inline]
 netlink_unicast+0x618/0x838 net/netlink/af_netlink.c:1347
 netlink_sendmsg+0x5fc/0x8b0 net/netlink/af_netlink.c:1891
 sock_sendmsg_nosec net/socket.c:711 [inline]
 __sock_sendmsg net/socket.c:726 [inline]
 ____sys_sendmsg+0x410/0x708 net/socket.c:2583
 ___sys_sendmsg+0x178/0x1d8 net/socket.c:2637
 __sys_sendmsg net/socket.c:2669 [inline]
 __do_sys_sendmsg net/socket.c:2674 [inline]
 __se_sys_sendmsg net/socket.c:2672 [inline]
 __arm64_sys_sendmsg+0x12c/0x1c8 net/socket.c:2672
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x90/0x278 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0x13c/0x250 arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x54/0x70 arch/arm64/kernel/syscall.c:151
 el0_svc+0x4c/0xa8 arch/arm64/kernel/entry-common.c:744
 el0t_64_sync_handler+0x78/0x108 arch/arm64/kernel/entry-common.c:762
 el0t_64_sync+0x198/0x1a0 arch/arm64/kernel/entry.S:600

The buggy address belongs to the object at ffff0000d768c000
 which belongs to the cache kmalloc-cg-4k of size 4096
The buggy address is located 224 bytes inside of
 freed 4096-byte region [ffff0000d768c000, ffff0000d768d000)

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x117688
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff0000c77ef981
flags: 0xbfffe0000000040(head|node=0|zone=2|lastcpupid=0x1ffff)
page_type: f5(slab)
raw: 0bfffe0000000040 ffff0000c000f500 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000040004 00000001f5000000 ffff0000c77ef981
head: 0bfffe0000000040 ffff0000c000f500 dead000000000100 dead000000000122
head: 0000000000000000 0000000000040004 00000001f5000000 ffff0000c77ef981
head: 0bfffe0000000003 fffffdffc35da201 ffffffffffffffff 0000000000000000
head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000d768bf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff0000d768c000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff0000d768c080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                       ^
 ffff0000d768c100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff0000d768c180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

Fixes: 8c55fac ("net: linkwatch: only report IF_OPER_LOWERLAYERDOWN if iflink is actually down")
Reported-by: syzkaller <[email protected]>
Suggested-by: Jakub Kicinski <[email protected]>
Link: https://lore.kernel.org/netdev/[email protected]/ [1]
Signed-off-by: Kuniyuki Iwashima <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

libtraceevent parses and returns an array of argument fields, sometimes
larger than RAW_SYSCALL_ARGS_NUM (6) because it includes "__syscall_nr",
idx will traverse to index 6 (7th element) whereas sc->fmt->arg holds 6
elements max, creating an out-of-bounds access. This runtime error is
found by UBsan. The error message:

  $ sudo UBSAN_OPTIONS=print_stacktrace=1 ./perf trace -a --max-events=1
  builtin-trace.c:1966:35: runtime error: index 6 out of bounds for type 'syscall_arg_fmt [6]'
    #0 0x5c04956be5fe in syscall__alloc_arg_fmts /home/howard/hw/linux-perf/tools/perf/builtin-trace.c:1966
    #1 0x5c04956c0510 in trace__read_syscall_info /home/howard/hw/linux-perf/tools/perf/builtin-trace.c:2110
    #2 0x5c04956c372b in trace__syscall_info /home/howard/hw/linux-perf/tools/perf/builtin-trace.c:2436
    #3 0x5c04956d2f39 in trace__init_syscalls_bpf_prog_array_maps /home/howard/hw/linux-perf/tools/perf/builtin-trace.c:3897
    #4 0x5c04956d6d25 in trace__run /home/howard/hw/linux-perf/tools/perf/builtin-trace.c:4335
    #5 0x5c04956e112e in cmd_trace /home/howard/hw/linux-perf/tools/perf/builtin-trace.c:5502
    #6 0x5c04956eda7d in run_builtin /home/howard/hw/linux-perf/tools/perf/perf.c:351
    #7 0x5c04956ee0a8 in handle_internal_command /home/howard/hw/linux-perf/tools/perf/perf.c:404
    #8 0x5c04956ee37f in run_argv /home/howard/hw/linux-perf/tools/perf/perf.c:448
    #9 0x5c04956ee8e9 in main /home/howard/hw/linux-perf/tools/perf/perf.c:556
    #10 0x79eb3622a3b7 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    #11 0x79eb3622a47a in __libc_start_main_impl ../csu/libc-start.c:360
    #12 0x5c04955422d4 in _start (/home/howard/hw/linux-perf/tools/perf/perf+0x4e02d4) (BuildId: 5b6cab2d59e96a4341741765ad6914a4d784dbc6)

     0.000 ( 0.014 ms): Chrome_ChildIO/117244 write(fd: 238, buf: !, count: 1)                                      = 1

Fixes: 5e58fcf ("perf trace: Allow allocating sc->arg_fmt even without the syscall tracepoint")
Signed-off-by: Howard Chu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Namhyung Kim <[email protected]>

… prevent wrong idmap generation

The PTE_MAYBE_NG macro sets the nG page table bit according to the value
of "arm64_use_ng_mappings". This variable is currently placed in the
.bss section. create_init_idmap() is called before the .bss section
initialisation which is done in early_map_kernel(). Therefore,
data/test_prot in create_init_idmap() could be set incorrectly through
the PAGE_KERNEL -> PROT_DEFAULT -> PTE_MAYBE_NG macros.

   # llvm-objdump-21 --syms vmlinux-gcc | grep arm64_use_ng_mappings
     ffff800082f242a8 g     O .bss    0000000000000001 arm64_use_ng_mappings

The create_init_idmap() function disassembly compiled with llvm-21:

  // create_init_idmap()
  ffff80008255c058: d10103f     	sub	sp, sp, #0x40
  ffff80008255c05c: a9017bfd     	stp	x29, x30, [sp, #0x10]
  ffff80008255c060: a90257f6     	stp	x22, x21, [sp, #0x20]
  ffff80008255c064: a9034ff4     	stp	x20, x19, [sp, #0x30]
  ffff80008255c068: 910043fd     	add	x29, sp, #0x10
  ffff80008255c06c: 90003fc8     	adrp	x8, 0xffff800082d54000
  ffff80008255c070: d280e06a     	mov	x10, #0x703     // =1795
  ffff80008255c074: 91400409     	add	x9, x0, #0x1, lsl #12 // =0x1000
  ffff80008255c078: 394a4108     	ldrb	w8, [x8, #0x290] ------------- (1)
  ffff80008255c07c: f2e00d0a     	movk	x10, #0x68, lsl #48
  ffff80008255c080: f90007e9     	str	x9, [sp, #0x8]
  ffff80008255c084: aa0103f3     	mov	x19, x1
  ffff80008255c088: aa0003f4     	mov	x20, x0
  ffff80008255c08c: 14000000     	b	0xffff80008255c08c <__pi_create_init_idmap+0x34>
  ffff80008255c090: aa082d56     	orr	x22, x10, x8, lsl #11 -------- (2)

Note (1) is loading the arm64_use_ng_mappings value in w8 and (2) is set
the text or data prot with the w8 value to set PTE_NG bit. If the .bss
section isn't initialized, x8 could include a garbage value and generate
an incorrect mapping.

Annotate arm64_use_ng_mappings as __read_mostly so that it is placed in
the .data section.

Fixes: 84b04d3 ("arm64: kernel: Create initial ID map from C code")
Cc: [email protected] # 6.9.x
Tested-by: Nathan Chancellor <[email protected]>
Signed-off-by: Yeoreum Yun <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[[email protected]: use __read_mostly instead of __ro_after_init]
[[email protected]: slight tweaking of the code comment]
Signed-off-by: Catalin Marinas <[email protected]>

In probe appletb_kbd_probe() a "struct appletb_kbd *kbd" is allocated
via devm_kzalloc() to store touch bar keyboard related data.
Later on if backlight_device_get_by_name() finds a backlight device
with name "appletb_backlight" a timer (kbd->inactivity_timer) is setup
with appletb_inactivity_timer() and the timer is armed to run after
appletb_tb_dim_timeout (60) seconds.

A use-after-free is triggered when failure occurs after the timer is
armed. This ultimately means probe failure occurs and as a result the
"struct appletb_kbd *kbd" which is device managed memory is freed.
After 60 seconds the timer will have expired and __run_timers will
attempt to access the timer (kbd->inactivity_timer) however the kdb
structure has been freed causing a use-after free.

[   71.636938] ==================================================================
[   71.637915] BUG: KASAN: slab-use-after-free in __run_timers+0x7ad/0x890
[   71.637915] Write of size 8 at addr ffff8881178c5958 by task swapper/1/0
[   71.637915]
[   71.637915] CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted 6.16.0-rc2-00318-g739a6c93cc75-dirty #12 PREEMPT(voluntary)
[   71.637915] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[   71.637915] Call Trace:
[   71.637915]  <IRQ>
[   71.637915]  dump_stack_lvl+0x53/0x70
[   71.637915]  print_report+0xce/0x670
[   71.637915]  ? __run_timers+0x7ad/0x890
[   71.637915]  kasan_report+0xce/0x100
[   71.637915]  ? __run_timers+0x7ad/0x890
[   71.637915]  __run_timers+0x7ad/0x890
[   71.637915]  ? __pfx___run_timers+0x10/0x10
[   71.637915]  ? update_process_times+0xfc/0x190
[   71.637915]  ? __pfx_update_process_times+0x10/0x10
[   71.637915]  ? _raw_spin_lock_irq+0x80/0xe0
[   71.637915]  ? _raw_spin_lock_irq+0x80/0xe0
[   71.637915]  ? __pfx__raw_spin_lock_irq+0x10/0x10
[   71.637915]  run_timer_softirq+0x141/0x240
[   71.637915]  ? __pfx_run_timer_softirq+0x10/0x10
[   71.637915]  ? __pfx___hrtimer_run_queues+0x10/0x10
[   71.637915]  ? kvm_clock_get_cycles+0x18/0x30
[   71.637915]  ? ktime_get+0x60/0x140
[   71.637915]  handle_softirqs+0x1b8/0x5c0
[   71.637915]  ? __pfx_handle_softirqs+0x10/0x10
[   71.637915]  irq_exit_rcu+0xaf/0xe0
[   71.637915]  sysvec_apic_timer_interrupt+0x6c/0x80
[   71.637915]  </IRQ>
[   71.637915]
[   71.637915] Allocated by task 39:
[   71.637915]  kasan_save_stack+0x33/0x60
[   71.637915]  kasan_save_track+0x14/0x30
[   71.637915]  __kasan_kmalloc+0x8f/0xa0
[   71.637915]  __kmalloc_node_track_caller_noprof+0x195/0x420
[   71.637915]  devm_kmalloc+0x74/0x1e0
[   71.637915]  appletb_kbd_probe+0x37/0x3c0
[   71.637915]  hid_device_probe+0x2d1/0x680
[   71.637915]  really_probe+0x1c3/0x690
[   71.637915]  __driver_probe_device+0x247/0x300
[   71.637915]  driver_probe_device+0x49/0x210
[...]
[   71.637915]
[   71.637915] Freed by task 39:
[   71.637915]  kasan_save_stack+0x33/0x60
[   71.637915]  kasan_save_track+0x14/0x30
[   71.637915]  kasan_save_free_info+0x3b/0x60
[   71.637915]  __kasan_slab_free+0x37/0x50
[   71.637915]  kfree+0xcf/0x360
[   71.637915]  devres_release_group+0x1f8/0x3c0
[   71.637915]  hid_device_probe+0x315/0x680
[   71.637915]  really_probe+0x1c3/0x690
[   71.637915]  __driver_probe_device+0x247/0x300
[   71.637915]  driver_probe_device+0x49/0x210
[...]

The root cause of the issue is that the timer is not disarmed
on failure paths leading to it remaining active and accessing
freed memory. To fix this call timer_delete_sync() to deactivate
the timer.

Another small issue is that timer_delete_sync is called
unconditionally in appletb_kbd_remove(), fix this by checking
for a valid kbd->backlight_dev before calling timer_delete_sync.

Fixes: 93a0fc4 ("HID: hid-appletb-kbd: add support for automatic brightness control while using the touchbar")
Cc: [email protected]
Signed-off-by: Qasim Ijaz <[email protected]>
Reviewed-by: Aditya Garg <[email protected]>
Signed-off-by: Jiri Kosina <[email protected]>

Receiving HSR frame with insufficient space to hold HSR tag in the skb
can result in a crash (kernel BUG):

[   45.390915] skbuff: skb_under_panic: text:ffffffff86f32cac len:26 put:14 head:ffff888042418000 data:ffff888042417ff4 tail:0xe end:0x180 dev:bridge_slave_1
[   45.392559] ------------[ cut here ]------------
[   45.392912] kernel BUG at net/core/skbuff.c:211!
[   45.393276] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI
[   45.393809] CPU: 1 UID: 0 PID: 2496 Comm: reproducer Not tainted 6.15.0 #12 PREEMPT(undef)
[   45.394433] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   45.395273] RIP: 0010:skb_panic+0x15b/0x1d0

<snip registers, remove unreliable trace>

[   45.402911] Call Trace:
[   45.403105]  <IRQ>
[   45.404470]  skb_push+0xcd/0xf0
[   45.404726]  br_dev_queue_push_xmit+0x7c/0x6c0
[   45.406513]  br_forward_finish+0x128/0x260
[   45.408483]  __br_forward+0x42d/0x590
[   45.409464]  maybe_deliver+0x2eb/0x420
[   45.409763]  br_flood+0x174/0x4a0
[   45.410030]  br_handle_frame_finish+0xc7c/0x1bc0
[   45.411618]  br_handle_frame+0xac3/0x1230
[   45.413674]  __netif_receive_skb_core.constprop.0+0x808/0x3df0
[   45.422966]  __netif_receive_skb_one_core+0xb4/0x1f0
[   45.424478]  __netif_receive_skb+0x22/0x170
[   45.424806]  process_backlog+0x242/0x6d0
[   45.425116]  __napi_poll+0xbb/0x630
[   45.425394]  net_rx_action+0x4d1/0xcc0
[   45.427613]  handle_softirqs+0x1a4/0x580
[   45.427926]  do_softirq+0x74/0x90
[   45.428196]  </IRQ>

This issue was found by syzkaller.

The panic happens in br_dev_queue_push_xmit() once it receives a
corrupted skb with ETH header already pushed in linear data. When it
attempts the skb_push() call, there's not enough headroom and
skb_push() panics.

The corrupted skb is put on the queue by HSR layer, which makes a
sequence of unintended transformations when it receives a specific
corrupted HSR frame (with incomplete TAG).

Fix it by dropping and consuming frames that are not long enough to
contain both ethernet and hsr headers.

Alternative fix would be to check for enough headroom before skb_push()
in br_dev_queue_push_xmit().

In the reproducer, this is injected via AF_PACKET, but I don't easily
see why it couldn't be sent over the wire from adjacent network.

Further Details:

In the reproducer, the following network interface chain is set up:

┌────────────────┐   ┌────────────────┐
│ veth0_to_hsr   ├───┤  hsr_slave0    ┼───┐
└────────────────┘   └────────────────┘   │
                                          │ ┌──────┐
                                          ├─┤ hsr0 ├───┐
                                          │ └──────┘   │
┌────────────────┐   ┌────────────────┐   │            │┌────────┐
│ veth1_to_hsr   ┼───┤  hsr_slave1    ├───┘            └┤        │
└────────────────┘   └────────────────┘                ┌┼ bridge │
                                                       ││        │
                                                       │└────────┘
                                                       │
                                        ┌───────┐      │
                                        │  ...  ├──────┘
                                        └───────┘

To trigger the events leading up to crash, reproducer sends a corrupted
HSR frame with incomplete TAG, via AF_PACKET socket on 'veth0_to_hsr'.

The first HSR-layer function to process this frame is
hsr_handle_frame(). It and then checks if the
protocol is ETH_P_PRP or ETH_P_HSR. If it is, it calls
skb_set_network_header(skb, ETH_HLEN + HSR_HLEN), without checking that
the skb is long enough. For the crashing frame it is not, and hence the
skb->network_header and skb->mac_len fields are set incorrectly,
pointing after the end of the linear buffer.

I will call this a BUG#1 and it is what is addressed by this patch. In
the crashing scenario before the fix, the skb continues to go down the
hsr path as follows.

hsr_handle_frame() then calls this sequence
hsr_forward_skb()
  fill_frame_info()
    hsr->proto_ops->fill_frame_info()
      hsr_fill_frame_info()

hsr_fill_frame_info() contains a check that intends to check whether the
skb actually contains the HSR header. But the check relies on the
skb->mac_len field which was erroneously setup due to BUG#1, so the
check passes and the execution continues  back in the hsr_forward_skb():

hsr_forward_skb()
  hsr_forward_do()
    hsr->proto_ops->get_untagged_frame()
      hsr_get_untagged_frame()
        create_stripped_skb_hsr()

In create_stripped_skb_hsr(), a copy of the skb is created and is
further corrupted by operation that attempts to strip the HSR tag in a
call to __pskb_copy().

The skb enters create_stripped_skb_hsr() with ethernet header pushed in
linear buffer. The skb_pull(skb_in, HSR_HLEN) thus pulls 6 bytes of
ethernet header into the headroom, creating skb_in with a headroom of
size 8. The subsequent __pskb_copy() then creates an skb with headroom
of just 2 and skb->len of just 12, this is how it looks after the copy:

gdb) p skb->len
$10 = 12
(gdb) p skb->data
$11 = (unsigned char *) 0xffff888041e45382 "\252\252\252\252\252!\210\373",
(gdb) p skb->head
$12 = (unsigned char *) 0xffff888041e45380 ""

It seems create_stripped_skb_hsr() assumes that ETH header is pulled
in the headroom when it's entered, because it just pulls HSR header on
top. But that is not the case in our code-path and we end up with the
corrupted skb instead. I will call this BUG#2

*I got confused here because it seems that under no conditions can
create_stripped_skb_hsr() work well, the assumption it makes is not true
during the processing of hsr frames - since the skb_push() in
hsr_handle_frame to skb_pull in hsr_deliver_master(). I wonder whether I
missed something here.*

Next, the execution arrives in hsr_deliver_master(). It calls
skb_pull(ETH_HLEN), which just returns NULL - the SKB does not have
enough space for the pull (as it only has 12 bytes in total at this
point).

*The skb_pull() here further suggests that ethernet header is meant
to be pushed through the whole hsr processing and
create_stripped_skb_hsr() should pull it before doing the HSR header
pull.*

hsr_deliver_master() then puts the corrupted skb on the queue, it is
then picked up from there by bridge frame handling layer and finally
lands in br_dev_queue_push_xmit where it panics.

Cc: [email protected]
Fixes: 48b491a ("net: hsr: fix mac_len checks")
Reported-by: [email protected]
Signed-off-by: Jakub Acs <[email protected]>
Reviewed-by: Eric Dumazet <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>