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CVE-2025-37858: fs/jfs: Prevent integer overflow in AG size calculation

Description

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.

Classification

CVE ID: CVE-2025-37858

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 12.8% (scored less or equal to compared to others)

EPSS Date: 2025-06-07 (when was this score calculated)

References

Timeline

2025-05-09 07:40:14 UTC
CVE

fs/jfs: Prevent integer overflow in AG size calculation