CVE-2026-64496

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.

Weakness

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

Affected Software

Extended Description

A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:

A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.

Potential Mitigations

• Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
• Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/29.html

References

• https://git.kernel.org/stable/c/0d4a646d7f87ea3625fafe387043fddc6a2f5e7f
• https://git.kernel.org/stable/c/72c6aa8e0d74eab91b8694cde97dec088c248fee
• https://git.kernel.org/stable/c/9dc84ba4be5bbeb29ee49efe6cea2cb32c461424
• https://git.kernel.org/stable/c/9edefd4c56bee3fe331e0355d1f10a533134999d
• https://git.kernel.org/stable/c/a13ef1adbc62085b21b546b07b0be7e2fbf52150
• https://git.kernel.org/stable/c/af791d295737ea6b6ff2c8d8488462a49c14af01
• https://git.kernel.org/stable/c/d16a702ca7d29c0b7a9b509339d1b044a1cadb32
• https://git.kernel.org/stable/c/f187dc5a4c4846ffa07d9bda6e760837ed005574