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CVE-2026-80986
net/smc: bound the peer rkey counts in SMC-Rv2 LLC messages
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem net/smc. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-80986 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
On a link whose device has max_recv_sge == 1 there is no shared v2 receive buffer, and smc_llc_save_add_link_rkeys() takes the v2 extension from 44 bytes past the start of the queue entry's inline message: ext = (struct smc_llc_msg_add_link_v2_ext *)(llc_msg + SMC_WR_TX_SIZE); The entry is a 72-byte allocation and the extension starts at offset 68, so ext->num_rkeys at offset 94 is already past it. This happens on every SMC-Rv2 link addition, whatever the peer sends: [ 2.490065] BUG: KASAN: slab-out-of-bounds in smc_llc_save_add_link_rkeys+0x333/0x350 [ 2.490431] Read of size 2 at addr ffff8880056406de by task smctest/106 [ 2.490709] [ 2.490792] CPU: 0 UID: 0 PID: 106 Comm: smctest Not tainted 7.2.0-rc5-p1-g77a5d9d9c99f #32 PREEMPT(lazy) [ 2.490795] 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 [ 2.490798] Call Trace: [ 2.490803] <TASK> [ 2.490805] dump_stack_lvl+0x53/0x70 [ 2.490810] print_report+0xd0/0x630 [ 2.490828] ? __pfx__raw_spin_lock_irqsave+0x10/0x10 [ 2.490832] ? smc_llc_save_add_link_rkeys+0x333/0x350 [ 2.490834] kasan_report+0xce/0x100 [ 2.490836] ? smc_llc_save_add_link_rkeys+0x333/0x350 [ 2.490837] smc_llc_save_add_link_rkeys+0x333/0x350 [ 2.490839] ? smcr_buf_map_lgr+0x1bf/0x2b0 [ 2.490844] smc_llc_cli_add_link+0xca7/0x1e80 [ 2.490848] ? smc_llc_wait+0x355/0x810 [ 2.490850] ? __pfx_smc_llc_wait+0x10/0x10 [ 2.490851] ? __pfx_smc_llc_cli_add_link+0x10/0x10 [ 2.490853] ? __pfx_autoremove_wake_function+0x10/0x10 [ 2.490863] __smc_connect+0x3f5c/0x4980 [ 2.490873] ? __pfx_kernel_connect+0x10/0x10 [ 2.490888] ? __pfx___smc_connect+0x10/0x10 [ 2.490891] ? release_sock+0x148/0x1d0 [ 2.490894] smc_connect+0x42c/0x580 [ 2.490896] __sys_connect+0xfc/0x130 [ 2.490898] ? __pfx___sys_connect+0x10/0x10 [ 2.490900] ? handle_mm_fault+0x1a1/0x430 [ 2.490908] __x64_sys_connect+0x6d/0xb0 [ 2.490909] ? fpregs_assert_state_consistent+0x56/0xe0 [ 2.490917] do_syscall_64+0xf9/0x540 [ 2.490921] entry_SYSCALL_64_after_hwframe+0x77/0x7f [ 2.490924] RIP: 0033:0x421bb4 [ 2.490927] Code: ff f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 80 3d ad 34 09 00 00 74 13 b8 2a 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 4c c3 0f 1f 00 55 48 89 e5 48 83 ec 10 89 55 [ 2.490929] RSP: 002b:00007ffd473b01a8 EFLAGS: 00000202 ORIG_RAX: 000000000000002a [ 2.490935] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000421bb4 [ 2.490936] RDX: 0000000000000010 RSI: 00007ffd473b01d0 RDI: 0000000000000003 [ 2.490937] RBP: 0000000000003930 R08: 0000000000000004 R09: 0000000000000000 [ 2.490938] R10: 00007ffd473b0f98 R11: 0000000000000202 R12: 0000000000000006 [ 2.490939] R13: 00007ffd473b0f87 R14: 0000000000000003 R15: 00007ffd473b0f90 [ 2.490940] </TASK> [ 2.490941] [ 2.499545] Allocated by task 44: [ 2.499693] kasan_save_stack+0x33/0x60 [ 2.499860] kasan_save_track+0x14/0x30 [ 2.500026] __kasan_kmalloc+0x8f/0xa0 [ 2.500190] __kmalloc_cache_noprof+0x158/0x370 [ 2.500393] smc_llc_enqueue+0x72/0x560 [ 2.500559] smc_wr_rx_tasklet_fn+0x474/0xa80 [ 2.500747] tasklet_action_common+0x20f/0x8a0 [ 2.500945] handle_softirqs+0x18e/0x590 [ 2.501115] do_softirq+0x3b/0x60 [ 2.501266] __local_bh_enable_ip+0x61/0x70 [ 2.501446] __alloc_skb+0x732/0x890 [ 2.501604] rxe_init_packet+0x16b/0x4f0 [ 2.501783] prepare_ack_packet+0xb8/0x830 [ 2.501962] rxe_receiver+0x495/0x96e0 [ 2.502125] do_work+0x144/0x470 [ 2.502269] process_one_work+0x633/0x1030 [ 2.502450] worker_thread+0x45b/0xd10 [ 2.50261 ---truncated---
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
net/smc/smc_llc.c
- What this is
- SHARED MEMORY COMMUNICATIONS (SMC) SOCKETSMAINTAINERS section matched on net/smc/ · linux-rdma@vger.kernel.org · Supported
- Kernel module
- smc
Check it on the machine
grep -w CONFIG_SMC /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w smcPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian does not build this code in 2 releases. It does build it in 2 releases, so the answer depends on which release the machine runs.
- bookworm, trixiem
- forky, sidn
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- n
- not enabled on any flavour - this release does not build the code
- Build switch
- CONFIG_SMC
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-11 (37 days ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.65%, higher than 50.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- net/smc
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.14 | 6.18.50 | 486c699a8cde |
| 6.14 | 7.2.4 | 5e5d9e6df677 |
| 6.14 | 7.3 | 2d1e7c5aaa33 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- The OOB is reached from SMC-Rv2 LLC ADD_LINK and DELETE_RKEY handling on the RDMA RX path (smc_wr_rx_tasklet_fn→smc_llc_rx_handler→smc_llc_enqueue). CLC is plain TCP and SMC-Rv2/RoCEv2 LLC is IP-routable (UDP/4791), so a remote peer that can reach an AF_SMC listener drives the path.
- AC:LAttack complexity, low
- On SMC-Rv2 links with max_recv_sge==1 (the supported device class this bug exists for), every ADD_LINK reads past the 72-byte qentry regardless of peer contents, and a DELETE_RKEY_V2 with num_rkeys=255 walks up to 255 rkeys off the object; no race or attacker-uncontrollable layout is required.
- PR:NPrivileges required, none
- SMC authenticates nothing. smc_create()/smc_listen() enforce no capabilities, and smc_listen_work() runs the CLC/LLC handshake after TCP accept before accept() returns to userspace, so an unauthenticated network peer needs only reachability to the listener.
- UI:NUser interaction, none
- The listen worker is queued automatically from smc_tcp_listen_work() for inbound connections, and DELETE_RKEY is processed in the LLC event worker from RDMA completions; no local user action such as mounting a filesystem or opening a file is required.
- S:UScope, unchanged
- The slab out-of-bounds read and the resulting writes into the link-group rtoken table stay inside the host kernel (kmalloc qentry, lgr->rtokens) and do not cross a VM, IOMMU, or sandbox boundary.
- C:HConfidentiality impact, high
- smc_llc_save_add_link_rkeys() reads ext->num_rkeys 22 bytes past the 72-byte qentry and then walks up to 255 16-byte rt[] entries of adjacent heap; smc_llc_rmt_delete_rkey() similarly out-of-bounds-reads rkey[9..254]. Per kernel CNA guidance a large heap out-of-bounds read is High.
- I:HIntegrity impact, high
- Those out-of-bounds bytes are passed to smc_rtoken_set() (writes rkey/dma_addr into lgr->rtokens) and smc_rtoken_delete() (clears matching rtokens). Adjacent kmalloc-96 spray lets a peer influence the written values, corrupting RDMA targeting used by ib_post_send.
- A:HAvailability impact, high
- KASAN reports slab-out-of-bounds in smc_llc_save_add_link_rkeys on every affected ADD_LINK; a multi-kilobyte walk off a 72-byte object can oops when it hits an unmapped page, and a remote peer can repeat the handshake or DELETE_RKEY at will.