Medium [CVE-2026-72367] guard io_size EOF trim against concurrent truncate underflow

In the Linux kernel, the following vulnerability has been resolved: iomap: guard io_size EOF trim against concurrent truncate underflow iomap: fix zero padding data issue in concurrent append writes changed ioend accounting so that io_size tracks only valid data within EOF.

This trims io_size when a writeback range extends past end_pos: ioend->io_size += map_len; if (ioend->io_offset + ioend->io_size > end_pos) ioend->io_size = end_pos - ioend->io_offset; However, if end_pos ends up below ioend->io_offset, the subtraction becomes negative and is stored in size_t io_size, causing an unsigned wrap to a huge value.

This can happen when writeback continues past byte-level EOF up to a block-aligned range, or when a concurrent truncate shrinks the file after end_pos was sampled in iomap_writeback_handle_eof().

A wrapped io_size can mislead append detection and corrupt completion-time size handling, since filesystem end_io paths consume io_size for decisions such as on-disk EOF updates and unwritten/COW completion ranges. This preserves the original intent of trimming io_size to valid in-EOF data while avoiding the underflow.

This vulnerability occurs due to an integer underflow when calculating io_size during concurrent file truncation operations.

Affected products named by the advisory: Red Hat Enterprise Linux 10; Red Hat package: kernel.