CVE-2026-72367

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.

Fix this by clamping io_size to zero when EOF has moved to or before

the ioend start offset. This preserves the original intent of trimming

io_size to valid in-EOF data while avoiding the underflow.