Executive brief
In the Linux kernel, the following vulnerability has been resolved:
scsi: qla2xxx: Fix queue teardown NULL dma_free and bitmap locking
qla25xx_free_req_que() and qla25xx_free_rsp_que() have two pre-existing bugs exposed on the error path of qla25xx_create_{req,rsp}_que():
1. When dma_alloc_coherent() fails during queue creation, the error path calls the free function with req->ring / rsp->ring still NULL (from kzalloc). The unconditional dma_free_coherent() with a NULL cpu_addr is undefined behavior and can panic.
2. The free functions clear req_qid_map / rsp_qid_map under vport_lock, but the create functions protect the same bitmaps with mq_lock. This provides no mutual exclusion. Additionally, the create error path clears the bit and releases mq_lock before calling the free function, creating a window where another thread can allocate the same que_id and have its ha->req_q_map entry clobbered by the subsequent lockless NULL assignment in the free function.
Fix by:
- Guarding dma_free_coherent() with a NULL check on the ring pointer.
- Using mq_lock (the lock held by all creators) in the free functions to atomically NULL the map entry and clear the bitmap bit.
- Removing the now-redundant clear_bit blocks from the create error paths since the free functions handle it atomically.