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    Subject[PATCH 5.8 259/633] dmaengine: dmatest: Check list for emptiness before access its last entry
    Date
    From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

    [ 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@arm.com>
    Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
    Tested-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
    Link: https://lore.kernel.org/r/20200922115847.30100-2-andriy.shevchenko@linux.intel.com
    Signed-off-by: Vinod Koul <vkoul@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/dma/dmatest.c | 5 ++---
    1 file changed, 2 insertions(+), 3 deletions(-)

    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;
    --
    2.25.1


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