* CVE-2026-80981: net/smc: fix use-after-free of the LLC qentry in smc_llc_srv_add_link()
@ 2026-09-11 19:41 Greg Kroah-Hartman
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From: Greg Kroah-Hartman @ 2026-09-11 19:41 UTC (permalink / raw)
To: linux-cve-announce; +Cc: Greg Kroah-Hartman
From: Greg Kroah-Hartman <gregkh@kernel.org>
Description
===========
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
[ 2.534078] process_one_work+0x633/0x1030
[ 2.534257] worker_thread+0x45b/0xd10
[ 2.534424] kthread+0x2c6/0x3b0
[ 2.534569] ret_from_fork+0x36e/0x5a0
[ 2.534737] ret_from_fork_asm+0x1a/0x30
[ 2.534907]
[ 2.534980] Freed by task 11:
[ 2.535112] kasan_save_stack+0x33/0x60
[ 2.535279] kasan_save_track+0x14/0x30
[ 2.535444] kasan_save_free_info+0x3b/0x60
[ 2.535625] __kasan_slab_free+0x43/0x70
[ 2.535798] kfree+0x121/0x380
[ 2.535935] smc_llc_srv_add_link+0x9a8/0x1e50
[ 2.536128] smc_listen_work+0x489e/0x4d00
[ 2.536305] process_one_work+0x633/0x1030
[ 2.536482] worker_thread+0x45b/0xd10
[ 2.536652] kthread+0x2c6/0x3b0
[ 2.536794] ret_from_fork+0x36e/0x5a0
[ 2.536958] ret_from_fork_asm+0x1a/0x30
[ 2.537133]
[ 2.537205] The buggy address belongs to the object at ffff888005219480
[ 2.537205] which belongs to the cache kmalloc-96 of size 96
[ 2.537719] The buggy address is located 94 bytes inside of
[ 2.537719] freed 96-byte region [ffff888005219480, ffff8880052194e0)
[ 2.538216]
[ 2.538289] The buggy address belongs to the physical page:
[ 2.538524] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x5219
[ 2.538857] flags: 0x100000000000000(node=0|zone=1)
[ 2.539066] page_type: f5(slab)
[ 2.539210] raw: 0100000000000000 ffff888001041280 dead000000000122 0000000000000000
[ 2.539534] raw: 0000000000000000 0000000000200020 00000000f5000000 0000000000000000
[ 2.539863] page dumped because: kasan: bad access detected
[ 2.540098]
[ 2.540170] Memory state around the buggy address:
[ 2.540379] ffff888005219380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 2.540684] ffff888005219400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 2.540988] >ffff888005219480: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
[ 2.541291] ^
[ 2.541548] ffff888005219500: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
[ 2.541857] ffff888005219580: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
The offset is past the 72-byte queue entry because the out-of-bounds read
fixed by the next patch is on the same line; what this patch removes is the
free at smc_llc_srv_add_link+0x9a8 happening before the read at +0xaa2.
Detach the entry instead of freeing it there, and free it at the single
exit label. The reject path has to detach as well, otherwise it would be
freed twice.
This changes only the lifetime of the entry. The same read still runs past
its end until the next two patches bound it, so a backport wants all three.
The Linux kernel CVE team has assigned CVE-2026-80981 to this issue.
Affected and fixed versions
===========================
Issue introduced in 6.14 with commit 27ef6a9981fe74191849966a6d5e0400a4008ab8 and fixed in 6.18.50 with commit c52a998a223e7e84333306996edec096178d1e95
Issue introduced in 6.14 with commit 27ef6a9981fe74191849966a6d5e0400a4008ab8 and fixed in 7.2.4 with commit adef84cc85d449ac28d2b4b4c49cf19619c56e27
Issue introduced in 6.14 with commit 27ef6a9981fe74191849966a6d5e0400a4008ab8 and fixed in 7.3-rc1 with commit a42a459ef0e54cb0c4b3e43e21cb0e658e664f64
Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.
Unaffected versions might change over time as fixes are backported to
older supported kernel versions. The official CVE entry at
https://cve.org/CVERecord/?id=CVE-2026-80981
will be updated if fixes are backported, please check that for the most
up to date information about this issue.
Affected files
==============
The file(s) affected by this issue are:
net/smc/smc_llc.c
Mitigation
==========
The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes. Individual
changes are never tested alone, but rather are part of a larger kernel
release. Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all. If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
https://git.kernel.org/stable/c/c52a998a223e7e84333306996edec096178d1e95
https://git.kernel.org/stable/c/adef84cc85d449ac28d2b4b4c49cf19619c56e27
https://git.kernel.org/stable/c/a42a459ef0e54cb0c4b3e43e21cb0e658e664f64
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2026-09-11 19:41 CVE-2026-80981: net/smc: fix use-after-free of the LLC qentry in smc_llc_srv_add_link() Greg Kroah-Hartman
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