[Bug 199676] [net80211] [patch]: fix possible kernel panic in IBSS mode (iv_bss may be freed twice)

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=199676

            Bug ID: 199676
           Summary: [net80211] [patch]: fix possible kernel panic in IBSS
                    mode (iv_bss may be freed twice)
           Product: Base System
           Version: 11.0-CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Keywords: patch
          Severity: Affects Only Me
          Priority: ---
         Component: wireless
          Assignee: freebsd-wireless at FreeBSD.org
          Reporter: s3erios at gmail.com
          Keywords: patch

Created attachment 155958
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=155958&action=edit
Remove old iv_bss entry from the node table

This may happen on RUN -> SCAN -> RUN -> SCAN state transition:

1. RUN -> SCAN: in ieee80211_sta_join1(): iv_bss will be moved to obss, refcnt
will be reduced by 2 (default minimum).

Now, if old iv_bss have some extra references (for example, from unacknowledged
probe responses), it will not be freed and will stay in the node table.

2. SCAN -> RUN.

3. If old iv_bss will not be deleted by the time when the next RUN -> SCAN
state transition occurs, then sta_leave() will reduce it's reference counter
once more. As a result, two last users will free it -> this will lead to kernel
panic.

In this patch old iv_bss entry is explicitly removed from the node table in
ieee80211_sta_join1() (as a result, it will not be processed by sta_leave()).

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