audit: move put_tree() to avoid trim_trees refcount underflow and UAF

AUDIT_TRIM is expected to be idempotent, but multiple executions resulted
in a refcount underflow and use-after-free.

git bisect fingered commit fb041bb7c0a9	("locking/refcount: Consolidate
implementations of refcount_t") but this patch with its more thorough
checking that wasn't in the x86 assembly code merely exposed a previously
existing tree refcount imbalance in the case of tree trimming code that
was refactored with prune_one() to remove a tree introduced in
commit 8432c7006297 ("audit: Simplify locking around untag_chunk()")

Move the put_tree() to cover only the prune_one() case.

Passes audit-testsuite and 3 passes of "auditctl -t" with at least one
directory watch.

Cc: Jan Kara <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Seiji Nishikawa <[email protected]>
Cc: [email protected]
Fixes: 8432c7006297 ("audit: Simplify locking around untag_chunk()")
Signed-off-by: Richard Guy Briggs <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
[PM: reformatted/cleaned-up the commit description]
Signed-off-by: Paul Moore <[email protected]>

0 files changed, 0 insertions, 0 deletions