CVE-2026-98703: wifi: mac80211: minstrel_ht: validate fixed rate index

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

wifi: mac80211: minstrelht: validate fixed rate index

The fixedrateidx debugfs file is a plain u32 attribute, so any value can be written to it. minstrelhtupdatestats() then copies the value into mi->maxtprate[] and mi->maxprobrate, and minstrelhtsetrate() uses MIRATEGROUP()/MIRATEIDX() to index minstrelmcsgroups[] (42 entries) and mi->groups[].rates[] (10 entries) with it.

Writing e.g. 65535 selects group 4095 and rate index 15, far outside both arrays. The out-of-bounds entries are dereferenced and updated as struct minstrelratestats (retry counts, etc.), so the invalid index corrupts adjacent kernel memory. With CONFIGUBSANBOUNDS the access is reported as an array-index-out-of-bounds in minstrelhtsetrate().

Only a valid group/rate pair, or U32MAX to disable fixed rate processing, can be used safely, so reject any other value when the debugfs file is written.

The file is only reachable through a root-only debugfs mount, so this is not a privilege boundary. The out-of-bounds access is still a bug that must not be reachable through a writable debugfs attribute.