CVE-2026-80981

In the Linux kernel, the following vulnerability has been resolved:

net/smc: fix use-after-free of the LLC qentry in smc_llc_srv_add_link()

smc_llc_srv_add_link() keeps add_llc pointing into the queue entry:

  add_llc = &qentry->msg.add_link;			smc_llc.c:1482
  ...
  smc_llc_save_add_link_info(link_new, add_llc);	smc_llc.c:1494
  smc_llc_flow_qentry_del(&lgr->llc_flow_lcl);		smc_llc.c:1495
  ...
  u8 *llc_msg = smc_link_shared_v2_rxbuf(link) ?
	(u8 *)lgr->wr_rx_buf_v2 : (u8 *)add_llc;	smc_llc.c:1504
  smc_llc_save_add_link_rkeys(link, link_new, llc_msg);	smc_llc.c:1506

smc_llc_flow_qentry_del() kfree()s the entry, so on a link without a shared
v2 receive buffer the pointer handed to smc_llc_save_add_link_rkeys() is
already freed. Before the Fixes: commit that branch always used
lgr->wr_rx_buf_v2 and add_llc was not used after the free.

Reproduced on an unpatched tree over rxe, with KASAN, kasan_multi_shot
and a link forced to max_recv_sge == 1: the entry is freed and read by
the same call, and the freeing frame is smc_llc_srv_add_link() itself.

  [    2.523161] BUG: KASAN: slab-use-after-free in smc_llc_save_add_link_rkeys+0x333/0x350
  [    2.523499] Read of size 2 at addr ffff8880052194de by task kworker/0:1/11
  [    2.523789]
  [    2.523862] CPU: 0 UID: 0 PID: 11 Comm: kworker/0:1 Not tainted 7.2.0-rc5-p0-g2c9dd296545d #35 PREEMPT(lazy)
  [    2.523865] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
  [    2.523866] Workqueue: smc_hs_wq smc_listen_work
  [    2.523869] Call Trace:
  [    2.523870]  <TASK>
  [    2.523871]  dump_stack_lvl+0x53/0x70
  [    2.523872]  print_report+0xd0/0x630
  [    2.523874]  ? __pfx__raw_spin_lock_irqsave+0x10/0x10
  [    2.523876]  ? smc_llc_save_add_link_rkeys+0x333/0x350
  [    2.523878]  kasan_report+0xce/0x100
  [    2.523879]  ? smc_llc_save_add_link_rkeys+0x333/0x350
  [    2.523881]  smc_llc_save_add_link_rkeys+0x333/0x350
  [    2.523883]  ? smcr_buf_reg_lgr+0x2a4/0x660
  [    2.523885]  smc_llc_srv_add_link+0xaa2/0x1e50
  [    2.523888]  ? _printk+0xba/0xf0
  [    2.523897]  ? __pfx_smc_llc_srv_add_link+0x10/0x10
  [    2.523899]  ? down_write+0xb0/0x130
  [    2.523903]  ? __pfx_down_write+0x10/0x10
  [    2.523905]  smc_listen_work+0x489e/0x4d00
  [    2.523907]  ? kmem_cache_free+0x1c6/0x3a0
  [    2.523911]  ? __pfx_smc_listen_work+0x10/0x10
  [    2.523913]  ? release_sock+0x148/0x1d0
  [    2.523915]  ? smc_tcp_listen_work+0xb4f/0xfc0
  [    2.523917]  ? _raw_spin_lock_irq+0x80/0xe0
  [    2.523918]  ? __pfx__raw_spin_lock_irq+0x10/0x10
  [    2.523920]  process_one_work+0x633/0x1030
  [    2.523922]  ? assign_work+0x11d/0x370
  [    2.523924]  worker_thread+0x45b/0xd10
  [    2.523926]  ? __pfx_worker_thread+0x10/0x10
  [    2.523928]  ? __pfx_worker_thread+0x10/0x10
  [    2.523929]  kthread+0x2c6/0x3b0
  [    2.523931]  ? recalc_sigpending+0x15c/0x1e0
  [    2.523934]  ? __pfx_kthread+0x10/0x10
  [    2.523935]  ret_from_fork+0x36e/0x5a0
  [    2.523937]  ? __pfx_ret_from_fork+0x10/0x10
  [    2.523938]  ? __switch_to+0x572/0xdd0
  [    2.523943]  ? __pfx_kthread+0x10/0x10
  [    2.523944]  ret_from_fork_asm+0x1a/0x30
  [    2.523947]  </TASK>
  [    2.523948]
  [    2.531253] Allocated by task 48:
  [    2.531399]  kasan_save_stack+0x33/0x60
  [    2.531570]  kasan_save_track+0x14/0x30
  [    2.531737]  __kasan_kmalloc+0x8f/0xa0
  [    2.531905]  __kmalloc_cache_noprof+0x158/0x370
  [    2.532100]  smc_llc_enqueue+0x72/0x560
  [    2.532268]  smc_wr_rx_tasklet_fn+0x474/0xa80
  [    2.532491]  tasklet_action_common+0x20f/0x8a0
  [    2.532714]  handle_softirqs+0x18e/0x590
  [    2.532886]  do_softirq+0x3b/0x60
  [    2.533036]  __local_bh_enable_ip+0x61/0x70
  [    2.533221]  __alloc_skb+0x732/0x890
  [    2.533384]  rxe_init_packet+0x16b/0x4f0
  [    2.533567]  prepare_ack_packet+0xb8/0x830
  [    2.533760]  rxe_receiver+0x495/0x96e0
  [    2.533933]  do_work+0x144/0x470
  [    2
---truncated---