mm/damon/core: validate damos_quota_goal->nid for node_mem_{used,free}_bp

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

mm/damon/core: validate damos_quota_goal->nid for node_mem_{used,free}_bp

Patch series "mm/damon/core: validate damos_quota_goal->nid".

node_mem[cg]_{used,free}_bp DAMOS quota goals receive the node id. The
node id is used for si_meminfo_node() and NODE_DATA() without proper
validation. As a result, privileged users can trigger an out of bounds
memory access using DAMON_SYSFS. Fix the issues.

The issue was originally reported [1] with a fix by another author. The
original author announced [2] that they will stop working including the
fix that was still in the review stage. Hence I'm restarting this.

This patch (of 2):

Users can set damos_quota_goal->nid with arbitrary value for
node_mem_{used,free}_bp. But DAMON core is using those for
si_meminfo_node() without the validation of the value. This can result in
out of bounds memory access. The issue can actually triggered using DAMON
user-space tool (damo), like below.

$ sudo ./damo start --damos_action stat \
--damos_quota_goal node_mem_used_bp 50% -1 \
--damos_quota_interval 1s
$ sudo dmesg
[...]
[ 65.565986] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000098

Fix this issue by adding the validation of the given node. If an invalid
node id is given, it returns 0% for used memory ratio, and 100% for free
memory ratio.