CVE-2022-50145

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

dmaengine: sf-pdma: Add multithread support for a DMA channel

When we get a DMA channel and try to use it in multiple threads it will cause oops and hanging the system.

% echo 64 > /sys/module/dmatest/parameters/threads_per_chan % echo 10000 > /sys/module/dmatest/parameters/iterations % echo 1 > /sys/module/dmatest/parameters/run [ 89.480664] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000a0 [ 89.488725] Oops [#1] [ 89.494708] CPU: 2 PID: 1008 Comm: dma0chan0-copy0 Not tainted 5.17.0-rc5 [ 89.509385] epc : vchan_find_desc+0x32/0x46 [ 89.513553] ra : sf_pdma_tx_status+0xca/0xd6

This happens because of data race. Each thread rewrite channelss descriptor as soon as device_prep_dma_memcpy() is called. It leads to the situation when the driver thinks that it uses right descriptor that actually is freed or substituted for other one.

With current fixes a descriptor changes its value only when it has been used. A new descriptor is acquired from vc->desc_issued queue that is already filled with descriptors that are ready to be sent. Threads have no direct access to DMA channel descriptor. Now it is just possible to queue a descriptor for further processing.

Affected Software

References

• https://git.kernel.org/stable/c/4c7350b1dd8a192af844de32fc99b9e34c876fda
• https://git.kernel.org/stable/c/5ab2782c944e324008ef5d658f2494a9f0e3c5ac
• https://git.kernel.org/stable/c/a93b3f1e11971a91b6441b6d47488f4492cc113f
• https://git.kernel.org/stable/c/b2cc5c465c2cb8ab697c3fd6583c614e3f6cfbcc
• https://git.kernel.org/stable/c/b9b4992f897be9b0b9e3a3b956cab6b75ccc3f11