dmaengine: fix NULL pointer in channel unregistration function

stable inclusion
from stable-v5.10.210
commit 9de69732dde4e443c1c7f89acbbed2c45a6a8e17
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I97NHW
CVE: CVE-2023-52492

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9de69732dde4e443c1c7f89acbbed2c45a6a8e17



---------------------------

[ Upstream commit f5c24d94512f1b288262beda4d3dcb9629222fc7 ]

__dma_async_device_channel_register() can fail. In case of failure,
chan->local is freed (with free_percpu()), and chan->local is nullified.
When dma_async_device_unregister() is called (because of managed API or
intentionally by DMA controller driver), channels are unconditionally
unregistered, leading to this NULL pointer:
[    1.318693] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000d0
[...]
[    1.484499] Call trace:
[    1.486930]  device_del+0x40/0x394
[    1.490314]  device_unregister+0x20/0x7c
[    1.494220]  __dma_async_device_channel_unregister+0x68/0xc0

Look at dma_async_device_register() function error path, channel device
unregistration is done only if chan->local is not NULL.

Then add the same condition at the beginning of
__dma_async_device_channel_unregister() function, to avoid NULL pointer
issue whatever the API used to reach this function.

Fixes: d2fb0a04 ("dmaengine: break out channel registration")
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/20231213160452.2598073-1-amelie.delaunay@foss.st.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>