dm thin: fix use-after-free in metadata_pre_commit_callback
dm-thin uses struct pool to hold the state of the pool. There may be multiple pool_c's pointing to a given pool, each pool_c represents a loaded target. pool_c's may be created and destroyed arbitrarily and the pool contains a reference count of pool_c's pointing to it. Since commit 694cfe7f ("dm thin: Flush data device before committing metadata") a pointer to pool_c is passed to dm_pool_register_pre_commit_callback and this function stores it in pmd->pre_commit_context. If this pool_c is freed, but pool is not (because there is another pool_c referencing it), we end up in a situation where pmd->pre_commit_context structure points to freed pool_c. It causes a crash in metadata_pre_commit_callback. Fix this by moving the dm_pool_register_pre_commit_callback() from pool_ctr() to pool_preresume(). This way the in-core thin-pool metadata is only ever armed with callback data whose lifetime matches the active thin-pool target. In should be noted that this fix preserves the ability to load a thin-pool table that uses a different data block device (that contains the same data) -- though it is unclear if that capability is still useful and/or needed. Fixes: 694cfe7f ("dm thin: Flush data device before committing metadata") Cc: stable@vger.kernel.org Reported-by: Zdenek Kabelac <zkabelac@redhat.com> Reported-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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