When a PTP ethernet raw frame with a size of more than 256 bytes followed
by a 0xff pattern is sent to __skb_flow_dissect, nhoff value calculation
is wrong. For example: hdr->message_length takes the wrong value (0xffff)
and it does not replicate real header length. In this case, 'nhoff' value
was overridden and the PTP header was badly dissected. This leads to a
kernel crash.

net/core: flow_dissector
net/core flow dissector nhoff = 0x0000000e
net/core flow dissector hdr->message_length = 0x0000ffff
net/core flow dissector nhoff = 0x0001000d (u16 overflow)
...
skb linear:   00000000: 00 a0 c9 00 00 00 00 a0 c9 00 00 00 88
skb frag:     00000000: f7 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

Using the size of the ptp_header struct will allow the corrected
calculation of the nhoff value.

net/core flow dissector nhoff = 0x0000000e
net/core flow dissector nhoff = 0x00000030 (sizeof ptp_header)
...
skb linear:   00000000: 00 a0 c9 00 00 00 00 a0 c9 00 00 00 88 f7 ff ff
skb linear:   00000010: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
skb linear:   00000020: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
skb frag:     00000000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

Kernel trace:
[   74.984279] ------------[ cut here ]------------
[   74.989471] kernel BUG at include/linux/skbuff.h:2440!
[   74.995237] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
[   75.001098] CPU: 4 PID: 0 Comm: swapper/4 Tainted: G     U            5.15.85-intel-ese-standard-lts #1
[   75.011629] Hardware name: Intel Corporation A-Island (CPU:AlderLake)/A-Island (ID:06), BIOS SB_ADLP.01.01.00.01.03.008.D-6A9D9E73-dirty Mar 30 2023
[   75.026507] RIP: 0010:eth_type_trans+0xd0/0x130
[   75.031594] Code: 03 88 47 78 eb c7 8b 47 68 2b 47 6c 48 8b 97 c0 00 00 00 83 f8 01 7e 1b 48 85 d2 74 06 66 83 3a ff 74 09 b8 00 04 00 00 eb ab <0f> 0b b8 00 01 00 00 eb a2 48 85 ff 74 eb 48 8d 54 24 06 31 f6 b9
[   75.052612] RSP: 0018:ffff9948c0228de0 EFLAGS: 00010297
[   75.058473] RAX: 00000000000003f2 RBX: ffff8e47047dc300 RCX: 0000000000001003
[   75.066462] RDX: ffff8e4e8c9ea040 RSI: ffff8e4704e0a000 RDI: ffff8e47047dc300
[   75.074458] RBP: ffff8e4704e2acc0 R08: 00000000000003f3 R09: 0000000000000800
[   75.082466] R10: 000000000000000d R11: ffff9948c0228dec R12: ffff8e4715e4e010
[   75.090461] R13: ffff9948c0545018 R14: 0000000000000001 R15: 0000000000000800
[   75.098464] FS:  0000000000000000(0000) GS:ffff8e4e8fb00000(0000) knlGS:0000000000000000
[   75.107530] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   75.113982] CR2: 00007f5eb35934a0 CR3: 0000000150e0a002 CR4: 0000000000770ee0
[   75.121980] PKRU: 55555554
[   75.125035] Call Trace:
[   75.127792]  <IRQ>
[   75.130063]  ? eth_get_headlen+0xa4/0xc0
[   75.134472]  igc_process_skb_fields+0xcd/0x150
[   75.139461]  igc_poll+0xc80/0x17b0
[   75.143272]  __napi_poll+0x27/0x170
[   75.147192]  net_rx_action+0x234/0x280
[   75.151409]  __do_softirq+0xef/0x2f4
[   75.155424]  irq_exit_rcu+0xc7/0x110
[   75.159432]  common_interrupt+0xb8/0xd0
[   75.163748]  </IRQ>
[   75.166112]  <TASK>
[   75.168473]  asm_common_interrupt+0x22/0x40
[   75.173175] RIP: 0010:cpuidle_enter_state+0xe2/0x350
[   75.178749] Code: 85 c0 0f 8f 04 02 00 00 31 ff e8 39 6c 67 ff 45 84 ff 74 12 9c 58 f6 c4 02 0f 85 50 02 00 00 31 ff e8 52 b0 6d ff fb 45 85 f6 <0f> 88 b1 00 00 00 49 63 ce 4c 2b 2c 24 48 89 c8 48 6b d1 68 48 c1
[   75.199757] RSP: 0018:ffff9948c013bea8 EFLAGS: 00000202
[   75.205614] RAX: ffff8e4e8fb00000 RBX: ffffb948bfd23900 RCX: 000000000000001f
[   75.213619] RDX: 0000000000000004 RSI: ffffffff94206161 RDI: ffffffff94212e20
[   75.221620] RBP: 0000000000000004 R08: 000000117568973a R09: 0000000000000001
[   75.229622] R10: 000000000000afc8 R11: ffff8e4e8fb29ce4 R12: ffffffff945ae980
[   75.237628] R13: 000000117568973a R14: 0000000000000004 R15: 0000000000000000
[   75.245635]  ? cpuidle_enter_state+0xc7/0x350
[   75.250518]  cpuidle_enter+0x29/0x40
[   75.254539]  do_idle+0x1d9/0x260
[   75.258166]  cpu_startup_entry+0x19/0x20
[   75.262582]  secondary_startup_64_no_verify+0xc2/0xcb
[   75.268259]  </TASK>
[   75.270721] Modules linked in: 8021q snd_sof_pci_intel_tgl snd_sof_intel_hda_common tpm_crb snd_soc_hdac_hda snd_sof_intel_hda snd_hda_ext_core snd_sof_pci snd_sof snd_sof_xtensa_dsp snd_soc_acpi_intel_match snd_soc_acpi snd_soc_core snd_compress iTCO_wdt ac97_bus intel_pmc_bxt mei_hdcp iTCO_vendor_support snd_hda_codec_hdmi pmt_telemetry intel_pmc_core pmt_class snd_hda_intel x86_pkg_temp_thermal snd_intel_dspcfg snd_hda_codec snd_hda_core kvm_intel snd_pcm snd_timer kvm snd mei_me soundcore tpm_tis irqbypass i2c_i801 mei tpm_tis_core pcspkr intel_rapl_msr tpm i2c_smbus intel_pmt thermal sch_fq_codel uio uhid i915 drm_buddy video drm_display_helper drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm fuse configfs
[   75.342736] ---[ end trace 3785f9f360400e3a ]---
[   75.347913] RIP: 0010:eth_type_trans+0xd0/0x130
[   75.352984] Code: 03 88 47 78 eb c7 8b 47 68 2b 47 6c 48 8b 97 c0 00 00 00 83 f8 01 7e 1b 48 85 d2 74 06 66 83 3a ff 74 09 b8 00 04 00 00 eb ab <0f> 0b b8 00 01 00 00 eb a2 48 85 ff 74 eb 48 8d 54 24 06 31 f6 b9
[   75.373994] RSP: 0018:ffff9948c0228de0 EFLAGS: 00010297
[   75.379860] RAX: 00000000000003f2 RBX: ffff8e47047dc300 RCX: 0000000000001003
[   75.387856] RDX: ffff8e4e8c9ea040 RSI: ffff8e4704e0a000 RDI: ffff8e47047dc300
[   75.395864] RBP: ffff8e4704e2acc0 R08: 00000000000003f3 R09: 0000000000000800
[   75.403857] R10: 000000000000000d R11: ffff9948c0228dec R12: ffff8e4715e4e010
[   75.411863] R13: ffff9948c0545018 R14: 0000000000000001 R15: 0000000000000800
[   75.419875] FS:  0000000000000000(0000) GS:ffff8e4e8fb00000(0000) knlGS:0000000000000000
[   75.428946] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   75.435403] CR2: 00007f5eb35934a0 CR3: 0000000150e0a002 CR4: 0000000000770ee0
[   75.443410] PKRU: 55555554
[   75.446477] Kernel panic - not syncing: Fatal exception in interrupt
[   75.453738] Kernel Offset: 0x11c00000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
[   75.465794] ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---

Fixes: 4f1cc51f ("net: flow_dissector: Parse PTP L2 packet header")
Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>