Date:   Mon, 6 Nov 2017 12:17:30 +0100
From:   Stefan Kratochwil <stefan.kratochwil@...itec.com>
To:     <netdev@...r.kernel.org>
Subject: CAN interface handling: possible bug in
 net/core/dev.c#enqueue_to_backlog()

Hey folks,

I probably found a bug in the function mentioned above which leads to a
WARN_ON() and in many cases to a kernel panic. The problem occurs when a
CAN bus interface is put down using 'ip link' during a tx operation. In
this situation, a code path exists from within a tx interrupt through
core/net/dev.c#enqueue_to_backlog() to the non interrupt-safe function
'kfree_skb()'. This situation always triggers the 'WARN_ON(in_irq))' in
net/core/skbuff.c#skb_release_head_state(), and with some luck it leads
to a NULL pointer dereference.

I first found this code path in the 'rcar_canfd' driver (kernel 4.9.58),
but almost every other CAN driver does the same thing, even in the most
up-to-date kernel.

Now, net/core/dev.c is pretty hot code, and I have no idea what happens
if we would substitute the 'kfree_skb()' in the 'drop' case of
'enqueue_to_backlog()' with a 'dev_kfree_skb_any()'.

Some time ago, there was an almost identical issue reported via Bugzilla
(https://bugzilla.kernel.org/show_bug.cgi?id=114791), but it was
abandoned without further comments.

Also, an actual fix was applied which addressed a similar bug
(https://patchwork.kernel.org/patch/5479931/).

Looking forward for your opinions!


[12150.231280] ------------[ cut here ]------------
[12150.232363] rcar_canfd e66c0000.can canif1: bitrate error 0.0%
[12150.243474] WARNING: CPU: 0 PID: 0 at
/home/skr/build_snapshot/build/tmp/work-shared/box-m3ulcb/kernel-source/net/core/skbuff.c:654
skb_release_head_state+0xe0/0xe8
[12150.261301] Modules linked in: can_raw can rcar_canfd mcp251x ravb
mdio_bitbang can_dev ipv6 autofs4
[12150.271475]
[12150.273902] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W
4.9.58-box #1
[12150.282703] Hardware name: BOX based on Renesas M3ULCB (r8a7796) (DT)
[12150.290728] task: ffff00000899f480 task.stack: ffff000008990000
[12150.297625] PC is at skb_release_head_state+0xe0/0xe8
[12150.303654] LR is at skb_release_all+0x14/0x30
[12150.309072] pc : [<ffff000008618090>] lr : [<ffff000008618374>]
pstate: 000001c5
[12150.317469] sp : ffff8005fff21ac0
[12150.321779] x29: ffff8005fff21ac0 x28: 000000000000000c
[12150.328097] x27: ffff8005fa23e880 x26: 0000000000000087
[12150.334390] x25: ffff8005fff21bc8 x24: 00000000000001c0
[12150.340666] x23: ffff8005f59d7800 x22: ffff00000897d000
[12150.346934] x21: ffff000008629530 x20: ffff00000897d780
[12150.353192] x19: ffff8005f59d7800 x18: 000000000000000a
[12150.359441] x17: 0000ffffa4e36c40 x16: ffff00000820a060
[12150.365680] x15: 00002fd2dc895abe x14: 000d59e4c4b21f40
[12150.371915] x13: 0000000007ed6b48 x12: 071c71c71c71c71c
[12150.378141] x11: 00000000000000b5 x10: 0000000000000040
[12150.384363] x9 : ffff8005fd002da0 x8 : ffff8005fd000028
[12150.390578] x7 : 0000000000000000 x6 : 000cd24f19d1cf10
[12150.396778] x5 : 0000000000000018 x4 : 000000000059ecb6
[12150.402967] x3 : 0000000000000000 x2 : 0000000000000000
[12150.409153] x1 : ffff000008616808 x0 : 0000000000010102
[12150.415332]
[12150.417661] ---[ end trace b157fa53318961ad ]---
[12150.423133] Call trace:
[12150.426427] Exception stack(0xffff8005fff218f0 to 0xffff8005fff21a20)
[12150.433738] 18e0:                                   ffff8005f59d7800
0001000000000000
[12150.442471] 1900: ffff8005fff21ac0 ffff000008618090 ffff8005fff21950
ffff00000862987c
[12150.451227] 1920: ffff8005fa23e000 ffff8005f505c600 0000000000000080
0000000000000001
[12150.460002] 1940: 0000000000000080 000000000abffe46 ffff8005fff21970
ffff0000007afc68
[12150.468801] 1960: ffff8005fa23e000 0000000000000001 ffff8005fff21a00
ffff0000080ebdf0
[12150.477613] 1980: ffff8005fc3c4880 ffff8005fce38800 0000000000010102
ffff000008616808
[12150.486445] 19a0: 0000000000000000 0000000000000000 000000000059ecb6
0000000000000018
[12150.495297] 19c0: 000cd24f19d1cf10 0000000000000000 ffff8005fd000028
ffff8005fd002da0
[12150.504168] 19e0: 0000000000000040 00000000000000b5 071c71c71c71c71c
0000000007ed6b48
[12150.513060] 1a00: 000d59e4c4b21f40 00002fd2dc895abe ffff00000820a060
0000ffffa4e36c40
[12150.521977] [<ffff000008618090>] skb_release_head_state+0xe0/0xe8
[12150.529178] [<ffff000008618374>] skb_release_all+0x14/0x30
[12150.535777] [<ffff000008618158>] kfree_skb+0x38/0x108
[12150.541953] [<ffff000008629530>] enqueue_to_backlog+0xb0/0x238
[12150.548928] [<ffff0000086296f8>] netif_rx_internal+0x40/0x1a8
[12150.555828] [<ffff00000862987c>] netif_rx+0x1c/0xb0
[12150.561853] [<ffff0000007791fc>] can_get_echo_skb+0x3c/0x78 [can_dev]
[12150.569445] [<ffff0000007af754>]
rcar_canfd_channel_interrupt+0x114/0x718 [rcar_canfd]
[12150.578490] [<ffff0000080ebdf0>] __handle_irq_event_percpu+0x58/0x240
[12150.586020] [<ffff0000080ebff4>] handle_irq_event_percpu+0x1c/0x58
[12150.593263] [<ffff0000080ec078>] handle_irq_event+0x48/0x78
[12150.599868] [<ffff0000080ef9c8>] handle_fasteoi_irq+0xb8/0x1a0
[12150.606722] [<ffff0000080eaf44>] generic_handle_irq+0x24/0x38
[12150.613465] [<ffff0000080eb5a4>] __handle_domain_irq+0x5c/0xb8
[12150.620284] [<ffff000008080ca8>] gic_handle_irq+0x58/0xb0



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