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CVE-2026-64102
RDMA/siw: Reject MPA FPDU length underflow before signed receive math
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem drivers/infiniband. Debian urgency: not yet assigned.
Debian does not build this code. The per-release build detail is under "Where it lives" below.
What to do, per Debian release
Debian's own status for CVE-2026-64102 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 | fixed | 6.1.176-1 | Update the kernel and reboot. Fixed in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
A malicious connected siw peer can send an iWARP FPDU whose MPA length field (c_hdr->mpa_len, 16 bit big-endian, peer-controlled) is smaller than the fixed DDP/RDMAP header for the announced opcode. Soft-iWARP parses the full header in siw_get_hdr() based on iwarp_pktinfo[opcode] .hdr_len, but never compares mpa_len against that header length. siw_tcp_rx_data() then derives srx->fpdu_part_rem = be16_to_cpu(mpa_len) - fpdu_part_rcvd + MPA_HDR_SIZE; where fpdu_part_rcvd equals iwarp_pktinfo[opcode].hdr_len at this point. For a tagged WRITE (hdr_len 16, MPA_HDR_SIZE 2) the smallest on-wire mpa_len of 0 yields fpdu_part_rem = -14, and any mpa_len below hdr_len - MPA_HDR_SIZE underflows to a negative int. The signed value then flows into siw_proc_write()/siw_proc_rresp() as bytes = min(srx->fpdu_part_rem, srx->skb_new); is handed to siw_check_mem() as an int len (whose interval check addr + len > mem->va + mem->len is satisfied for a valid base when len is negative), and reaches siw_rx_data() -> siw_rx_kva() / siw_rx_umem() -> skb_copy_bits() as a signed copy length. The header copy branch in skb_copy_bits() promotes that to size_t, producing a multi-gigabyte read. KASAN under a KUnit harness that drives the real kernel TCP receive path -- a loopback AF_INET socketpair, the malformed FPDU written via kernel_sendmsg, sk_data_ready firing in softirq, tcp_read_sock dispatching to siw_tcp_rx_data -- reports: BUG: KASAN: use-after-free in skb_copy_bits+0x284/0x480 Read of size 4294967295 at addr ffff888... Call Trace: skb_copy_bits siw_rx_kva siw_rx_data siw_check_mem siw_proc_write siw_tcp_rx_data __tcp_read_sock siw_qp_llp_data_ready tcp_data_ready tcp_data_queue Add the missing invariant at the earliest point where the peer header is fully assembled. iwarp_pktinfo[*].hdr_len - MPA_HDR_SIZE is exactly the value the siw transmitter uses as the minimum mpa_len for each opcode (drivers/infiniband/sw/siw/siw_qp.c:33), so this matches the protocol contract. Out-of-range FPDUs terminate the connection with TERM_ERROR_LAYER_LLP / LLP_ETYPE_MPA / LLP_ECODE_FPDU_START -- which is RFC 5044 Section 8 error code 3 ("Marker and ULPDU Length fields do not agree on the start of an FPDU"), the correct framing-error class for this inconsistency.
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.
drivers/infiniband/sw/siw/siw_qp_rx.c
- What this is
- SOFT-IWARP DRIVER (siw)MAINTAINERS section matched on drivers/infiniband/sw/siw/ · linux-rdma@vger.kernel.org · Supported
- Kernel module
- none to look for. The file would have gone into siw, and Debian does not compile it into that module, so finding siw in lsmod would say nothing about this CVE.
Check it on the machine
grep -wE 'CONFIG_INFINIBAND|CONFIG_RDMA_SIW' /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.
Show whether Debian builds this, per release
Debian does not build this code. In 4 releases below, every kernel flavour Debian publishes has the switch off, so the vulnerable file is compiled into no kernel binary Debian ships.
- bookworm, trixie, forky, sidn
- n
- not enabled on any flavour - this release does not build the code
- Build switches
- CONFIG_INFINIBAND, CONFIG_RDMA_SIW
- Reads as
- all on means the file is compiled; any one off means it is not.
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
- 2026-07-19 (3 months 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
- 0.50%, higher than 41.5% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/infiniband
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.3 | 5.10.258 | 683f7cfbf514 |
| 5.3 | 5.15.209 | 4a331582011d |
| 5.3 | 6.1.175 | 33a8b5e971e2 |
| 5.3 | 6.6.142 | 14553be882d9 |
| 5.3 | 6.12.92 | c7c0c0f4379d |
| 5.3 | 6.18.34 | 1012896f4225 |
| 5.3 | 7.0.11 | 775b4dc9618a |
| 5.3 | 7.1 | 0ce1bc9e46ec |
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
- A remote attacker triggers this by sending a malformed iWARP FPDU over an established TCP connection; the kernel processes it in the TCP softirq receive path via siw_tcp_rx_data without any local access.
- AC:LAttack complexity, low
- The attacker fully controls the peer-supplied mpa_len field and can reliably underflow fpdu_part_rem with a single crafted packet (e.g., mpa_len=0 on a tagged WRITE with hdr_len=16); no races or uncontrollable memory layout are required.
- PR:NPrivileges required, none
- Exploitation requires only network reachability to a host running an iWARP listener (e.g., SMB Direct/RDMA-over-TCP on siw); completing the MPA/TCP handshake does not require any local account or elevated privileges on the victim system.
- UI:NUser interaction, none
- No victim user interaction is needed; the malformed FPDU is processed automatically when received on the connected TCP socket during normal kernel softirq handling.
- S:UScope, unchanged
- Impact is confined to kernel memory and RDMA-registered buffers on the victim host; this is standard in-kernel memory corruption without crossing a VM, container, or IOMMU security boundary.
- C:HConfidentiality impact, high
- The negative copy length is promoted to a huge unsigned value in skb_copy_bits, producing a multi-gigabyte out-of-bounds read; KASAN confirmed use-after-free with a 4294967295-byte read, enabling arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- The same corrupted length drives skb_copy_bits writes into RDMA target memory (siw_rx_kva/siw_rx_umem) after siw_check_mem is bypassed by negative len, enabling out-of-bounds writes exploitable for memory corruption and potential code execution.
- A:HAvailability impact, high
- KASAN reports use-after-free in skb_copy_bits during normal receive processing, and this class of kernel memory corruption reliably causes oops/panic or exploitable instability under attacker control.