fs/jfs: Prevent integer overflow in AG size calculation

Summary

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.

Timeline

1. May 9, 2025, 6:42 AM UTCCVE published
2. May 11, 2026, 9:16 PM UTCRecord last updated

Affected versions

• Linux Linux

  Version range not reported

• Linux Linux

  2.6.12

References 9