sched: Fix out-of-bound access in uclamp

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: sched: Fix out-of-bound access in uclamp Util-clamp places tasks in different buckets based on their clamp values for performance reasons. However, the size of buckets is currently computed using a rounding division, which can lead to an off-by-one error in some configurations. For instance, with 20 buckets, the bucket size will be 1024/20=51. A task with a clamp of 1024 will be mapped to bucket id 1024/51=20. Sadly, correct indexes are in range [0,19], hence leading to an out of bound memory access. Clamp the bucket id to fix the issue.

References

• https://git.kernel.org/stable/c/687f523c134b7f0bd040ee1230f6d17990d54172
• https://git.kernel.org/stable/c/f7347c85490b92dd144fa1fba9e1eca501656ab3
• https://git.kernel.org/stable/c/3da3f804b82a0a382d523a21acf4cf3bb35f936d
• https://git.kernel.org/stable/c/42ee47c7e3569d9a0e2cb5053c496d97d380472f
• https://git.kernel.org/stable/c/6d2f8909a5fabb73fe2a63918117943986c39b6c