iomap: guard io_size EOF trim against concurrent truncate underflow

Overview

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.

Affected

• Linux >= 82c59a86a247a8970d353d10f52a37e5564fb137 < cc1d6af0bee27d6595908b497424f338161299fc
• Linux >= 51d20d1dacbec589d459e11fc88fbca419f84a99 < 1f38f65bf965fce9aa159d45c5347538f56c5973
• Linux >= 51d20d1dacbec589d459e11fc88fbca419f84a99 < 7f7780abb4c0fdc9a2603aea8e985ff14ee900e0
• Linux >= 51d20d1dacbec589d459e11fc88fbca419f84a99 < 55ec50d046c03b3724741957f7b007856e36dbe7
• Linux >= 6.12.10 < 6.12.114
• Linux 6.13

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.