CVE-2026-43371

In the Linux kernel, the following vulnerability has been resolved:

net: macb: Shuffle the tx ring before enabling tx

Quanyang observed that when using an NFS rootfs on an AMD ZynqMp board, the rootfs may take an extended time to recover after a suspend. Upon investigation, it was determined that the issue originates from a problem in the macb driver.

According to the Zynq UltraScale TRM [1], when transmit is disabled, the transmit buffer queue pointer resets to point to the address specified by the transmit buffer queue base address register.

In the current implementation, the code merely resets queue->tx_head and queue->tx_tail to 0. This approach presents several issues:

• Packets already queued in the tx ring are silently lost, leading to memory leaks since the associated skbs cannot be released.

• Concurrent write access to queue->tx_head and queue->tx_tail may occur from macb_tx_poll() or macb_start_xmit() when these values are reset to 0.

• The transmission may become stuck on a packet that has already been sent out, with its TX_USED bit set, but has not yet been processed. However, due to the manipulation of queue->tx_head and queue->tx_tail, macb_tx_poll() incorrectly assumes there are no packets to handle because queue->tx_head == queue->tx_tail. This issue is only resolved when a new packet is placed at this position. This is the root cause of the prolonged recovery time observed for the NFS root filesystem.

To resolve this issue, shuffle the tx ring and tx skb array so that the first unsent packet is positioned at the start of the tx ring. Additionally, ensure that updates to queue->tx_head and queue->tx_tail are properly protected with the appropriate lock.

[1] https://docs.amd.com/v/u/en-US/ug1085-zynq-ultrascale-trm

Weakness

The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.

Affected Software

Potential Mitigations

• Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone.
• For example, glibc in Linux provides protection against free of invalid pointers.
• When using Xcode to target OS X or iOS, enable automatic reference counting (ARC) [REF-391].
• To help correctly and consistently manage memory when programming in C++, consider using a smart pointer class such as std::auto_ptr (defined by ISO/IEC ISO/IEC 14882:2003), std::shared_ptr and std::unique_ptr (specified by an upcoming revision of the C++ standard, informally referred to as C++ 1x), or equivalent solutions such as Boost.

References

• https://git.kernel.org/stable/c/0a47c3889fcd843c72aa57fa8c4d06f5801fced4
• https://git.kernel.org/stable/c/403182e0771b250cfde0fe7e1081d095ceaf8230
• https://git.kernel.org/stable/c/58f5d34f88e8f00910b692537f7b2efdb8c3705d
• https://git.kernel.org/stable/c/881a0263d502e1a93ebc13a78254e9ad19520232
• https://git.kernel.org/stable/c/88f974fe118cb4653f029929ecbca7cfe06132ae
• https://git.kernel.org/stable/c/c6783bfa31a59f34fe4feb1bdbf67791ef3fb0b7