CVE: CVE-2023-54094
Published: 2025-12-24
Description: In the Linux kernel, the following vulnerability has been resolved:

net: prevent skb corruption on frag list segmentation

Ian reported several skb corruptions triggered by rx-gro-list,
collecting different oops alike:

[   62.624003] BUG: kernel NULL pointer dereference, address:[PII_REDACTED]0000c0
[   62.631083] #PF: supervisor read access in kernel mode
[   62.636312] #PF: error_code(0x0000) - not-present page
[   62.641541] PGD 0 P4D 0
[   62.644174] Oops: 0000 [#1] PREEMPT SMP NOPTI
[   62.648629] CPU: 1 PID: 913 Comm: napi/eno2-79 Not tainted 6.4.0 #364
[   62.655162] Hardware name: Supermicro Super Server/A2SDi-12C-HLN4F, BIOS 1.7a 10/13/2022
[   62.663344] RIP: 0010:__udp_gso_segment (./include/linux/skbuff.h:2858
./include/linux/udp.h:23 net/ipv4/udp_offload.c:228 net/ipv4/udp_offload.c:261
net/ipv4/udp_offload.c:277)
[   62.687193] RSP: 0018:ffffbd3a83b4f868 EFLAGS: 00010246
[   62.692515] RAX:[PII_REDACTED]0000ce RBX: [PII_REDACTED] RCX: [PII_REDACTED]
[   62.699743] RDX: ffffa124def8a000 RSI: [PII_REDACTED] RDI: ffffa125952a14d4
[   62.706970] RBP: ffffa124def8a000 R08: [PII_REDACTED] R09:[PII_REDACTED]1558c9
[   62.714199] R10: [PII_REDACTED] R11: 00000000be554639 R12:[PII_REDACTED]0000e2
[   62.721426] R13: ffffa125952a1400 R14: ffffa125952a1400 R15:[PII_REDACTED]1558c9
[   62.728654] FS:  [PII_REDACTED](0000) GS:ffffa127efa40000(0000)
knlGS:[PII_REDACTED]
[   62.736852] CS:  0010 DS: 0000 ES: 0000 CR0: [PII_REDACTED]
[   62.742702] CR2:[PII_REDACTED]0000c0 CR3:[PII_REDACTED]4b0000 CR4:[PII_REDACTED]3526e0
[   62.749948] Call Trace:
[   62.752498]  <TASK>
[   62.779267] inet_gso_segment (net/ipv4/af_inet.c:1398)
[   62.787605] skb_mac_gso_segment (net/core/gro.c:141)
[   62.791906] __skb_gso_segment (net/core/dev.c:3403 (discriminator 2))
[   62.800492] validate_xmit_skb (./include/linux/netdevice.h:4862
net/core/dev.c:3659)
[   62.804695] validate_xmit_skb_list (net/core/dev.c:3710)
[   62.809158] sch_direct_xmit (net/sched/sch_generic.c:330)
[   62.813198] __dev_queue_xmit (net/core/dev.c:3805 net/core/dev.c:4210)
net/netfilter/core.c:626)
[   62.821093] br_dev_queue_push_xmit (net/bridge/br_forward.c:55)
[   62.825652] maybe_deliver (net/bridge/br_forward.c:193)
[   62.829420] br_flood (net/bridge/br_forward.c:233)
[   62.832758] br_handle_frame_finish (net/bridge/br_input.c:215)
[   62.837403] br_handle_frame (net/bridge/br_input.c:298
net/bridge/br_input.c:416)
[   62.851417] __netif_receive_skb_core.constprop.0 (net/core/dev.c:5387)
[   62.866114] __netif_receive_skb_list_core (net/core/dev.c:5570)
[   62.871367] netif_receive_skb_list_internal (net/core/dev.c:5638
net/core/dev.c:5727)
[   62.876795] napi_complete_done (./include/linux/list.h:37
./include/net/gro.h:434 ./include/net/gro.h:429 net/core/dev.c:6067)
[   62.881004] ixgbe_poll (drivers/net/ethernet/intel/ixgbe/ixgbe_main.c:3191)
[   62.893534] __napi_poll (net/core/dev.c:6498)
[   62.897133] napi_threaded_poll (./include/linux/netpoll.h:89
net/core/dev.c:6640)
[   62.905276] kthread (kernel/kthread.c:379)
[   62.913435] ret_from_fork (arch/x86/entry/entry_64.S:314)
[   62.917119]  </TASK>

In the critical scenario, rx-gro-list GRO-ed packets are fed, via a
bridge, both to the local input path and to an egress device (tun).

The segmentation of such packets unsafely writes to the cloned skbs
with shared heads.

This change addresses the issue by uncloning as needed the
to-be-segmented skbs.
References: https://git.kernel.org/stable/c/1731234e8b60063eae858c77b55c7a88f5084353; https://git.kernel.org/stable/c/7a59f29961cf97b98b02acaadf5a0b1f8dde938c; https://git.kernel.org/stable/c/bc3ab5d2ab69823f5cff89cf74ef78ffa0386c9a