CVE-2026-64496 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
iio: event: Fix event FIFO reset race
`iio_event_getfd()` creates the event file descriptor with `anon_inode_getfd()`, which allocates a new fd, creates the anonymous file and installs it in the process fd table before returning to the caller.
The IIO code resets the event FIFO after `anon_inode_getfd()` has returned, but before `IIO_GET_EVENT_FD_IOCTL` has copied the fd number to userspace. But since fd tables are shared between threads, another thread can guess the newly allocated fd number and issue a `read()` on it as soon as the fd has been installed.
This means the `kfifo_to_user()` in `iio_event_chrdev_read()` can run in parallel with the `kfifo_reset_out()` in `iio_event_getfd()`.
The kfifo documentation says that `kfifo_reset_out()` is only safe when it is called from the reader thread and there is only one concurrent reader. Otherwise it is dangerous and must be handled in the same way as `kfifo_reset()`.
If that happens, `kfifo_to_user()` can advance the FIFO `out` index based on state from before the reset, after the reset has already moved the `out` index to the current `in` index. That can leave the FIFO with an `out` index past the `in` index. A later `read()` can then see an underflowed FIFO length and copy more data than the event FIFO buffer contains. This can result in an out-of-bounds read and leak adjacent kernel memory to userspace.
Move the FIFO reset before `anon_inode_getfd()`. At that point the event fd is marked busy, but the new fd has not been installed yet, so userspace cannot access it while the FIFO is reset.
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Analysis
by VulDB Data Team • 07/26/2026
The vulnerability described in this CVE relates to a race condition within the Linux kernel's Industrial I/O (IIO) subsystem, specifically concerning event handling and FIFO management. This flaw exists in the interaction between the `iio_event_getfd()` function and the event file descriptor creation process. The issue stems from improper ordering of operations during the establishment of event file descriptors, creating a window where concurrent access can lead to memory corruption.
The technical root cause involves the sequence of operations within the IIO event subsystem where `iio_event_getfd()` uses `anon_inode_getfd()` to create and install a new file descriptor in the process's file descriptor table. This function allocates a new file descriptor number, creates an anonymous file, installs it in the process file descriptor table, and then returns control to the caller. However, the system resets the event FIFO after this return but before the ioctl operation completes and copies the file descriptor number back to userspace.
This timing issue creates a critical race condition because file descriptor tables are shared among threads within a process, allowing other threads to potentially guess the newly allocated file descriptor number and immediately attempt to read from it. The concurrent execution scenario occurs when `kfifo_to_user()` in `iio_event_chrdev_read()` operates simultaneously with `kfifo_reset_out()` in `iio_event_getfd()`. According to kernel documentation for kfifo operations, `kfifo_reset_out()` is only safe when called from the reader thread with exclusive access, making concurrent execution dangerous.
The operational impact of this vulnerability manifests as a potential out-of-bounds read condition that can leak adjacent kernel memory to userspace. When `kfifo_to_user()` processes data after `kfifo_reset_out()` has already moved the output index to match the input index, the FIFO structure can end up with an invalid state where the output index exceeds the input index. This creates a condition where subsequent read operations see an underflowed FIFO length and attempt to copy more data than actually exists in the buffer, resulting in memory disclosure.
This vulnerability aligns with CWE-362, which describes concurrent execution using improper synchronization, and relates to ATT&CK technique T1059.007 for kernel-level privilege escalation through memory corruption. The fix implemented moves the FIFO reset operation to occur before `anon_inode_getfd()` returns, ensuring that while the event fd is marked as busy during the reset process, userspace cannot access it until the reset completes. This prevents the race condition by maintaining proper synchronization between the file descriptor installation and the FIFO state management.
The mitigation strategy addresses the fundamental timing issue by reordering operations to eliminate the window of vulnerability. By performing the FIFO reset before installing the new file descriptor in the process table, the system ensures that no thread can access the event fd while it is being reset. This approach follows established kernel design principles for avoiding race conditions and maintains data integrity during concurrent access scenarios. The solution prevents both the out-of-bounds read condition and the memory leak by ensuring proper sequential execution of the critical operations within the IIO subsystem's event handling framework.
This vulnerability demonstrates the complexity of managing shared resources in kernel space, particularly where file descriptor management intersects with buffer state synchronization. The fix represents a careful balance between maintaining system functionality while eliminating dangerous race conditions that could be exploited for privilege escalation or information disclosure attacks. The resolution ensures that the IIO subsystem maintains robust memory safety properties even under concurrent access scenarios typical in industrial monitoring and sensor data collection environments.