CVE-2025-37858

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

fs/jfs: Prevent integer overflow in AG size calculation

The JFS filesystem calculates allocation group (AG) size using 1 << l2agsize in dbExtendFS(). When l2agsize exceeds 31 (possible with >2TB aggregates on 32-bit systems), this 32-bit shift operation causes undefined behavior and improper AG sizing.

On 32-bit architectures:

• Left-shifting 1 by 32+ bits results in 0 due to integer overflow
• This creates invalid AG sizes (0 or garbage values) in sbi->bmap->db_agsize
• Subsequent block allocations would reference invalid AG structures
• Could lead to:
  • Filesystem corruption during extend operations
  • Kernel crashes due to invalid memory accesses
  • Security vulnerabilities via malformed on-disk structures

Fix by casting to s64 before shifting: bmp->db_agsize = (s64)1 << l2agsize;

This ensures 64-bit arithmetic even on 32-bit architectures. The cast matches the data type of db_agsize (s64) and follows similar patterns in JFS block calculation code.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.