CVE-2026-93264 in Linux
Summary
by MITRE • 09/24/2026
In the Linux kernel, the following vulnerability has been resolved:
RDMA/efa: Fix PBL chunk length computation
On register MR, when creating the PBL, if it's an indirect PBL we create a chunk list to hold the PBL pages pointers. Each chunk is 4KB in size and can hold 510 addresses (EFA_PTRS_PER_CHUNK) and has a 12-byte control buffer at the end of it holding the next chunk's pointer and its length.
If the PBL number of pages is a multiple of EFA_PTRS_PER_CHUNK, the calculated last chunk length is wrongly computed as 0, even though that chunk is fully populated with 510 real page pointers. This wrong length is used both to DMA map the chunk and is propagated to the device, causing the device to see the chunk as empty and reject the memory registration.
Fix the calculation so it will be performed only if the number of pages isn't a multiple of EFA_PTRS_PER_CHUNK, if it is, its already handled in the above loop correctly. Also prevent out-of-bounds reach in the chunks array in such scenario.
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Analysis
by VulDB Data Team • 09/24/2026
The Linux kernel driver for Elastic Fabric Adapter RDMA devices contains a critical logic error in the computation of Physical Block List chunk lengths during memory registration operations. This vulnerability specifically affects indirect PBL handling, where the system constructs a list to hold pointers to PBL pages. Each chunk within this structure is designed to be 4KB in size and capable of holding up to five hundred ten addresses, with a twelve-byte control buffer at the end storing the pointer to the next chunk and its length. The flaw arises when the total number of pages required for registration results in a last chunk that is exactly full, meaning the page count is an exact multiple of EFA_PTRS_PER_CHUNK. In this specific scenario, the existing calculation logic incorrectly computes the length of the final chunk as zero rather than recognizing it as fully populated with valid pointers.
This incorrect length value has severe operational consequences for both software and hardware components involved in the memory registration process. The driver utilizes this flawed length to perform DMA mapping operations on the chunk, which can lead to improper resource allocation or access violations within the kernel space. More critically, this erroneous zero-length value is propagated directly to the EFA device via the PCIe interface. Upon receiving a PBL entry with a length of zero for what should be a fully populated chunk, the hardware interprets the data as empty and invalidates the memory registration request. This results in immediate rejection by the device, causing RDMA operations that depend on this specific memory region to fail, thereby disrupting high-performance computing workloads and network connectivity dependent on reliable RDMA transport services.
From a security perspective, while primarily a functional bug leading to denial of service for affected applications, such logic errors can sometimes be leveraged in more complex attack vectors if they lead to undefined behavior or out-of-bounds memory access during the DMA mapping phase. The vulnerability aligns with CWE-682 Incorrect Calculation and CWE-787 Out-of-Bounds Write when considering the potential for array index miscalculation that could expose adjacent kernel memory structures if not properly bounded by subsequent checks. In terms of attack classification, this represents a flaw in input validation and boundary condition handling within device driver code, which falls under ATT&CK techniques related to exploitation of software vulnerabilities rather than direct network attacks, highlighting the importance of robust defensive coding practices in low-level system components that interface with hardware peripherals.
The resolution involves correcting the conditional logic used to calculate chunk lengths so that it excludes cases where the number of pages is an exact multiple of EFA_PTRS_PER_CHUNK. By ensuring that fully populated chunks are handled correctly by the preceding loop iteration, the driver avoids generating invalid length values for DMA mapping and device communication. Additionally, the fix includes safeguards to prevent out-of-bounds access in the chunks array under these edge cases, thereby enhancing memory safety within the kernel module. To mitigate this vulnerability, system administrators should ensure that Linux kernels are updated with patches addressing RDMA EFA driver improvements. Regular patching cycles and monitoring for updates from major distribution vendors are essential to maintain the integrity of high-performance networking infrastructure protected by such hardware accelerators.