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.

https://git.kernel.org/stable/c/211ed8f5e39e61f9e4d18edd64ce8005a67a1b2a

https://git.kernel.org/stable/c/3d8a45f87010a802aa214bf39702ca9d99cbf3ba

https://git.kernel.org/stable/c/55edbf5dbf60a8195c21e92124c4028939ae16b2

https://git.kernel.org/stable/c/7ccf3b35274512b60ecb614e0637e76bd6f2d829

https://git.kernel.org/stable/c/7fcbf789629cdb9fbf4e2172ce31136cfed11e5e

https://git.kernel.org/stable/c/8bb29629a5e4090e1ef7199cb42db04a52802239

https://git.kernel.org/stable/c/c802a6a4009f585111f903e810b3be9c6d0da329

https://git.kernel.org/stable/c/dd07a985e2ded47b6c7d69fc93c1fe02977c8454

https://git.kernel.org/stable/c/ec34cdf4f917cc6abd306cf091f8b8361fedac88