Linux Kernel CVE-2025-68794

In the Linux kernel, the following vulnerability has been resolved:

iomap: adjust read range correctly for non-block-aligned positions

iomap_adjust_read_range() assumes that the position and length passed in are block-aligned. This is not always the case however, as shown in the syzbot generated case for erofs. This causes too many bytes to be skipped for uptodate blocks, which results in returning the incorrect position and length to read in. If all the blocks are uptodate, this underflows length and returns a position beyond the folio.

Fix the calculation to also take into account the block offset when calculating how many bytes can be skipped for uptodate blocks.

The Linux kernel iomap buffered-read path is affected on any version shipping the flawed iomap_adjust_read_range() before the fix; erofs is the demonstrated trigger but the helper is shared by all iomap-based filesystems. No CPE strings were supplied in the input, so exact version ranges are not enumerated here. Fixes were backported across multiple stable trees, evidenced by four kernel.org stable commits (12053695c8ef, 142194fb21af, 7aa6bc3e8766, 82b60ffbb532). Distribution exposure is confirmed for Ubuntu via advisory USN-8177-1 (https://ubuntu.com/security/notices/USN-8177-1), with additional cross-reference at VulDB (https://vuldb.com/?id.340677).