CVE-2024-53058

In the Linux kernel, the following vulnerability has been resolved:

net: stmmac: TSO: Fix unbalanced DMA map/unmap for non-paged SKB data

In case the non-paged data of a SKB carries protocol header and protocol

payload to be transmitted on a certain platform that the DMA AXI address

width is configured to 40-bit/48-bit, or the size of the non-paged data

is bigger than TSO_MAX_BUFF_SIZE on a certain platform that the DMA AXI

address width is configured to 32-bit, then this SKB requires at least

two DMA transmit descriptors to serve it.

For example, three descriptors are allocated to split one DMA buffer

mapped from one piece of non-paged data:

dma_desc[N + 0],

dma_desc[N + 1],

dma_desc[N + 2].

Then three elements of tx_q->tx_skbuff_dma[] will be allocated to hold

extra information to be reused in stmmac_tx_clean():

tx_q->tx_skbuff_dma[N + 0],

tx_q->tx_skbuff_dma[N + 1],

tx_q->tx_skbuff_dma[N + 2].

Now we focus on tx_q->tx_skbuff_dma[entry].buf, which is the DMA buffer

address returned by DMA mapping call. stmmac_tx_clean() will try to

unmap the DMA buffer _ONLY_IF_ tx_q->tx_skbuff_dma[entry].buf

is a valid buffer address.

The expected behavior that saves DMA buffer address of this non-paged

data to tx_q->tx_skbuff_dma[entry].buf is:

tx_q->tx_skbuff_dma[N + 0].buf = NULL;

tx_q->tx_skbuff_dma[N + 1].buf = NULL;

tx_q->tx_skbuff_dma[N + 2].buf = dma_map_single();

Unfortunately, the current code misbehaves like this:

tx_q->tx_skbuff_dma[N + 0].buf = dma_map_single();

tx_q->tx_skbuff_dma[N + 1].buf = NULL;

tx_q->tx_skbuff_dma[N + 2].buf = NULL;

On the stmmac_tx_clean() side, when dma_desc[N + 0] is closed by the

DMA engine, tx_q->tx_skbuff_dma[N + 0].buf is a valid buffer address

obviously, then the DMA buffer will be unmapped immediately.

There may be a rare case that the DMA engine does not finish the

pending dma_desc[N + 1], dma_desc[N + 2] yet. Now things will go

horribly wrong, DMA is going to access a unmapped/unreferenced memory

region, corrupted data will be transmited or iommu fault will be

triggered :(

In contrast, the for-loop that maps SKB fragments behaves perfectly

as expected, and that is how the driver should do for both non-paged

data and paged frags actually.

This patch corrects DMA map/unmap sequences by fixing the array index

for tx_q->tx_skbuff_dma[entry].buf when assigning DMA buffer address.

Tested and verified on DWXGMAC CORE 3.20a