In the Linux kernel, the following vulnerability has been resolved:
pwrseq: core: fix use-after-free in pwrseq_debugfs_seq_next()
pwrseq_debugfs_seq_next() declares 'next' with __free(put_device), which causes put_device() to be called on the returned pointer when the variable goes out of scope. This results in a use-after-free since the seq_file framework receives a pointer whose reference has already been dropped.
Simply removing __free(put_device) would fix the UAF but would leak the reference acquired by bus_find_next_device(), as stop() only calls up_read(&pwrseq_sem) and never releases the device reference.
Fix this by making the reference counting consistent across all seq_file callbacks, matching the standard pattern used by PCI and SCSI:
- start(): use get_device() so it returns a referenced pointer.
- next(): explicitly put_device(curr) to release the previous
- stop(): put_device(data) to release the last iterated device's