In the Linux kernel, the following vulnerability has been resolved:
mlxsw: spectrum_ptp: Fix napi_gro_receive() call from GC workqueue context
Currently mlxsw_sp1_ptp_ht_gc_collect() is run from the PTP
garbage-collection workqueue, rather than the NAPI poll context. For any
unmatched PTP entries carrying an SKB, it calls
mlxsw_sp1_ptp_unmatched_finish() -> mlxsw_sp1_ptp_packet_finish(). For
ingress packets, this calls mlxsw_sp_rx_listener_no_mark_func(). The end
of that function is the following:
<pre>
skb->protocol = eth_type_trans(skb, skb->dev);
napi_gro_receive(mlxsw_skb_cb(skb)->rx_md_info.napi, skb);
</pre>
The napi pointer is one that was placed in the SKB control block when the
trapped packet was received in the NAPI context. Later, when the GC reaps
the unmatched entry (up to MLXSW_SP1_PTP_HT_GC_TIMEOUT later), the call to
napi_gro_receive() mutates the NAPI instance's GRO list, which is unsafe
if the poll is running concurrently on another CPU.
In mlxsw_sp1_ptp_ht_gc_collect(), local_bh_disable() is called to prevent
softirq processing, but this only applies to the local CPU. Additionally,
its comment is stale. It states that mlxsw_sp1_ptp_unmatched_finish()
invokes netif_receive_skb(). This has not been accurate since the
referenced commit; this patch makes that comment accurate again.
mlxsw_pci_napi_devs_init() calls netif_threaded_enable() on the NAPI RX
net_device without any conditions. The NAPI instance's poll, which may be
running concurrent to the GC, is running as an independently-scheduled
kthread which may be on a different CPU. The call to local_bh_disable()
does not guard against this.
If a tx-timestamp timeout produces an unmatched entry (which can be easily
reproduced by running ptp4l and waiting for a port to reach the
UNCALIBRATED/SLAVE state) while the owning NAPI thread is in the middle of
a poll on another CPU, both sides mutate the GRO list concurrently, as
shown below:
[39.846] port 1 (swp1): MASTER to UNCALIBRATED on RS_SLAVE
list_add corruption. next->prev should be prev (ffff8d620faf4138), but was ffff8d624150f700. (next=ffff8d620faf4138).
kernel BUG at lib/list_debug.c:29!
Oops: invalid opcode: 0000 [#1] SMP PTI
CPU: 1 UID: 0 PID: 539 Comm: napi/mlxsw_rx-0 Not tainted 6.18.48 #1-NixOS PREEMPT(lazy)
Hardware name: Mellanox Technologies Ltd. MSN2410/VMOD0001, BIOS 4.6.5 09/13/2018
RIP: 0010:__list_add_valid_or_report+0x79/0xb0
RSP: 0018:ffffcdf8c0f27c08 EFLAGS: 00010246
RAX: 0000000000000075 RBX: ffff8d624150fd00 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8d6315d1e540
RBP: ffff8d620faf4070 R08: 0000000000000000 R09: 00000000ffffdfff
R10: ffffffffa5c60fe0 R11: ffffcdf8c0f27ab8 R12: 0000000000000003
R13: 000000000000003d R14: 00000000000001bc R15: 0000000000000001
FS: 0000000000000000(0000) GS:ffff8d636f63f000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000562689a60c24 CR3: 000000015f224004 CR4: 00000000001726f0
Call Trace:
<TASK>
gro_receive_skb+0xee/0x230
mlxsw_sp1_ptp_got_packet+0x61/0x140 [mlxsw_spectrum]
mlxsw_core_skb_receive+0xdf/0x1b0 [mlxsw_core]
mlxsw_pci_napi_poll_cq_rx+0x780/0x9d0 [mlxsw_pci]
__napi_poll+0x31/0x1e0
napi_threaded_poll_loop+0x16b/0x1c0
napi_threaded_poll+0x71/0xa0
kthread+0xfb/0x260
ret_from_fork+0x22d/0x260
ret_from_fork_asm+0x1a/0x30
</TASK>
Kernel panic - not syncing: Fatal exception in interrupt
The machinery that leads to this kernel panic has not been changed between
6.18.48 and mainline.
This patch adds an ingress-delivery helper for the PTP packet_finish()
path that calls netif_receive_skb() instead of napi_gro_receive().
netif_receive_skb(), unlike napi_gro_receive(), can be called from outside
of the NAPI instance's poll context, which can occur at the call site for
this path. RX stats accounting and the skb->dev assignment are still
preserved; the only change is the delivery call itself.
This removes GR
---truncated---
CVSS Vector: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS Score: 7.5
AV:A - The unmatched entries come from PTP event frames (Sync/Delay_Req/Pdelay) received on a Spectrum-1 port and trapped via PTP0 to mlxsw_sp1_ptp_receive(); only a peer on the port's link supplies these normally link-local PTP frames, so the range is adjacent, not routable Network.
AC:H - Needs Spectrum-1 hardware with admin-enabled RX HW timestamping (ing_types set), an ingress skb left unmatched past MLXSW_SP1_PTP_HT_GC_TIMEOUT, and mlxsw_sp1_ptp_ht_gc_collect() calling napi_gro_receive() while the threaded NAPI poll runs on another CPU; the attacker cannot schedule that cross-CPU overlap.
PR:N - Received PTP frames are trapped and queued in unmatched_ht without any authentication; the attacker only needs to send frames on the link, while enabling timestamping is the operator's standing configuration.
UI:N - No victim action is needed; the GC delayed work runs every MLXSW_SP1_PTP_HT_GC_INTERVAL on its own and delivers stale ingress skbs.
S:U - The corruption is confined to the host kernel's networking/GRO state, with no crossing of a VM or IOMMU boundary.
C:H - Concurrent unlocked mutation of the NAPI instance's GRO skb list from the GC workqueue and the NAPI poll kthread corrupts list linkage, which can leave skbs freed while still linked (use-after-free), a primitive usable for kernel memory disclosure.
I:H - The GRO list corruption (list_add corruption shown in gro_receive_skb) can turn into use-after-free and linked-list writes on kernel skb memory, which could be abused to corrupt kernel memory.
A:H - The race produces list corruption detected in __list_add_valid_or_report, and the resulting BUG in the napi/mlxsw_rx kthread panics the switch kernel ('Fatal exception in interrupt').
| Attack Vector |
Adjacent Network |
Scope |
Unchanged |
| Attack Complexity |
High |
Confidentiality Impact |
High |
| Privileges Required |
None |
Integrity Impact |
High |
| User Interaction |
None |
Availability Impact |
High |
AV:A - The unmatched entries come from PTP event frames (Sync/Delay_Req/Pdelay) received on a Spectrum-1 port and trapped via PTP0 to mlxsw_sp1_ptp_receive(); only a peer on the port's link supplies these normally link-local PTP frames, so the range is adjacent, not routable Network.
AC:H - Needs Spectrum-1 hardware with admin-enabled RX HW timestamping (ing_types set), an ingress skb left unmatched past MLXSW_SP1_PTP_HT_GC_TIMEOUT, and mlxsw_sp1_ptp_ht_gc_collect() calling napi_gro_receive() while the threaded NAPI poll runs on another CPU; the attacker cannot schedule that cross-CPU overlap.
PR:N - Received PTP frames are trapped and queued in unmatched_ht without any authentication; the attacker only needs to send frames on the link, while enabling timestamping is the operator's standing configuration.
UI:N - No victim action is needed; the GC delayed work runs every MLXSW_SP1_PTP_HT_GC_INTERVAL on its own and delivers stale ingress skbs.
S:U - The corruption is confined to the host kernel's networking/GRO state, with no crossing of a VM or IOMMU boundary.
C:H - Concurrent unlocked mutation of the NAPI instance's GRO skb list from the GC workqueue and the NAPI poll kthread corrupts list linkage, which can leave skbs freed while still linked (use-after-free), a primitive usable for kernel memory disclosure.
I:H - The GRO list corruption (list_add corruption shown in gro_receive_skb) can turn into use-after-free and linked-list writes on kernel skb memory, which could be abused to corrupt kernel memory.
A:H - The race produces list corruption detected in __list_add_valid_or_report, and the resulting BUG in the napi/mlxsw_rx kthread panics the switch kernel ('Fatal exception in interrupt').
CVSS 3.1