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ler@, markj@ reported a use after free in nfscl_cleanupkext().
They also provided two possible causes:
- In nfscl_cleanup_common(), "own" is the owner string
owp->nfsow_owner. If we free that particular
owner structure, than in subsequent comparisons
"own" will point to freed memory.
- nfscl_cleanup_common() can free more than one owner, so the use
of LIST_FOREACH_SAFE() in nfscl_cleanupkext() is not sufficient.
I also believe there is a 3rd:
- If nfscl_freeopenowner() or nfscl_freelockowner() is called
without the NFSCLSTATE mutex held, this could race with
nfscl_cleanupkext().
This could happen when the exclusive lock is held
on the client, such as when delegations are being returned
or when recovering from NFSERR_EXPIRED.
This patch fixes them as follows:
1 - Copy the owner string to a local variable before the
nfscl_cleanup_common() call.
2 - Modify nfscl_cleanup_common() so that it will never free more
than the first matching element. Normally there should only
be one element in each list with a matching open/lock owner
anyhow (but there might be a bug that results in a duplicate).
This should guarantee that the FOREACH_SAFE loops in
nfscl_cleanupkext() are adequate.
3 - Acquire the NFSCLSTATE mutex in nfscl_freeopenowner()
and nfscl_freelockowner(), if it is not already held.
This serializes all of these calls with the ones done in
nfscl_cleanup_common().
Reported by: ler
Reviewed by: markj
Tested by: cy
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D34334
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