On Sat, Oct 20, 2018 at 6:41 PM Steve Wise <swise@xxxxxxxxxxxxxxxxxxxxx> wrote: > > Hey Wenwen, > > > Subject: [PATCH] iw_cxgb4: fix a missing-check bug > > > > In c4iw_flush_hw_cq, the next CQE is acquired through t4_next_hw_cqe(). In > > t4_next_hw_cqe(), the CQE, i.e., 'cq->queue[cq->cidx]', is checked to see > > whether it is valid through t4_valid_cqe(). If it is valid, the address of > > the CQE is then saved to 'hw_cqe'. Later on, the CQE is copied to the > local > > memory in create_read_req_cqe(). The problem here is that the CQE is > > actually in a DMA region allocated by dma_alloc_coherent() in create_cq(). > > Given that the device also has the permission to access the DMA region, a > > malicious device controlled by an attacker can modify the CQE in the DMA > > region after the check in t4_next_hw_cqe() but before the copy in > > create_read_req_cqe(). By doing so, the attacker can supply invalid CQE, > > which can cause undefined behavior of the kernel and introduce potential > > security risks. > > > > If the dma device is malicious, couldn't it just dma some incorrect CQE but > still valid in the first place? I don't think this patch actually solves > the issue, and it forces a copy of a 64B CQE in a critical data io path. Thanks for your response! If the malicious dma device just dma some incorrect CQE, it will not be able to pass the verification in t4_valid_cqe(). Wenwen
