This is a note to let you know that I've just added the patch titled dmaengine: dmatest: Check list for emptiness before access its last entry to the 5.8-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: dmaengine-dmatest-check-list-for-emptiness-before-ac.patch and it can be found in the queue-5.8 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit e2190d9b4d94e26452e4d149ed91b5305bc7a569 Author: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> Date: Tue Sep 22 14:58:46 2020 +0300 dmaengine: dmatest: Check list for emptiness before access its last entry [ Upstream commit b28de385b71abf31ce68ec0387638bee26ae9024 ] After writing a garbage to the channel we get an Oops in dmatest_chan_set() due to access to last entry in the empty list. [ 212.670672] BUG: unable to handle page fault for address: fffffff000000020 [ 212.677562] #PF: supervisor read access in kernel mode [ 212.682702] #PF: error_code(0x0000) - not-present page ... [ 212.710074] RIP: 0010:dmatest_chan_set+0x149/0x2d0 [dmatest] [ 212.715739] Code: e8 cc f9 ff ff 48 8b 1d 0d 55 00 00 48 83 7b 10 00 0f 84 63 01 00 00 48 c7 c7 d0 65 4d c0 e8 ee 4a f5 e1 48 89 c6 48 8b 43 10 <48> 8b 40 20 48 8b 78 58 48 85 ff 0f 84 f5 00 00 00 e8 b1 41 f5 e1 Fix this by checking list for emptiness before accessing its last entry. Fixes: d53513d5dc28 ("dmaengine: dmatest: Add support for multi channel testing") Cc: Vladimir Murzin <vladimir.murzin@xxxxxxx> Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> Tested-by: Peter Ujfalusi <peter.ujfalusi@xxxxxx> Link: https://lore.kernel.org/r/20200922115847.30100-2-andriy.shevchenko@xxxxxxxxxxxxxxx Signed-off-by: Vinod Koul <vkoul@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/dma/dmatest.c b/drivers/dma/dmatest.c index 323822372b4ce..7480fc1042093 100644 --- a/drivers/dma/dmatest.c +++ b/drivers/dma/dmatest.c @@ -1240,15 +1240,14 @@ static int dmatest_chan_set(const char *val, const struct kernel_param *kp) add_threaded_test(info); /* Check if channel was added successfully */ - dtc = list_last_entry(&info->channels, struct dmatest_chan, node); - - if (dtc->chan) { + if (!list_empty(&info->channels)) { /* * if new channel was not successfully added, revert the * "test_channel" string to the name of the last successfully * added channel. exception for when users issues empty string * to channel parameter. */ + dtc = list_last_entry(&info->channels, struct dmatest_chan, node); if ((strcmp(dma_chan_name(dtc->chan), strim(test_channel)) != 0) && (strcmp("", strim(test_channel)) != 0)) { ret = -EINVAL;