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    Subject[PATCH 4.19 201/425] spi: Fix use-after-free with devm_spi_alloc_*
    Date
    From: William A. Kennington III <wak@google.com>

    [ Upstream commit 794aaf01444d4e765e2b067cba01cc69c1c68ed9 ]

    We can't rely on the contents of the devres list during
    spi_unregister_controller(), as the list is already torn down at the
    time we perform devres_find() for devm_spi_release_controller. This
    causes devices registered with devm_spi_alloc_{master,slave}() to be
    mistakenly identified as legacy, non-devm managed devices and have their
    reference counters decremented below 0.

    ------------[ cut here ]------------
    WARNING: CPU: 1 PID: 660 at lib/refcount.c:28 refcount_warn_saturate+0x108/0x174
    [<b0396f04>] (refcount_warn_saturate) from [<b03c56a4>] (kobject_put+0x90/0x98)
    [<b03c5614>] (kobject_put) from [<b0447b4c>] (put_device+0x20/0x24)
    r4:b6700140
    [<b0447b2c>] (put_device) from [<b07515e8>] (devm_spi_release_controller+0x3c/0x40)
    [<b07515ac>] (devm_spi_release_controller) from [<b045343c>] (release_nodes+0x84/0xc4)
    r5:b6700180 r4:b6700100
    [<b04533b8>] (release_nodes) from [<b0454160>] (devres_release_all+0x5c/0x60)
    r8:b1638c54 r7:b117ad94 r6:b1638c10 r5:b117ad94 r4:b163dc10
    [<b0454104>] (devres_release_all) from [<b044e41c>] (__device_release_driver+0x144/0x1ec)
    r5:b117ad94 r4:b163dc10
    [<b044e2d8>] (__device_release_driver) from [<b044f70c>] (device_driver_detach+0x84/0xa0)
    r9:00000000 r8:00000000 r7:b117ad94 r6:b163dc54 r5:b1638c10 r4:b163dc10
    [<b044f688>] (device_driver_detach) from [<b044d274>] (unbind_store+0xe4/0xf8)

    Instead, determine the devm allocation state as a flag on the
    controller which is guaranteed to be stable during cleanup.

    Fixes: 5e844cc37a5c ("spi: Introduce device-managed SPI controller allocation")
    Signed-off-by: William A. Kennington III <wak@google.com>
    Link: https://lore.kernel.org/r/20210407095527.2771582-1-wak@google.com
    Signed-off-by: Mark Brown <broonie@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/spi/spi.c | 9 ++-------
    include/linux/spi/spi.h | 3 +++
    2 files changed, 5 insertions(+), 7 deletions(-)

    diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
    index 7dabbc82b646..bbe33016d371 100644
    --- a/drivers/spi/spi.c
    +++ b/drivers/spi/spi.c
    @@ -2084,6 +2084,7 @@ struct spi_controller *__devm_spi_alloc_controller(struct device *dev,

    ctlr = __spi_alloc_controller(dev, size, slave);
    if (ctlr) {
    + ctlr->devm_allocated = true;
    *ptr = ctlr;
    devres_add(dev, ptr);
    } else {
    @@ -2344,11 +2345,6 @@ int devm_spi_register_controller(struct device *dev,
    }
    EXPORT_SYMBOL_GPL(devm_spi_register_controller);

    -static int devm_spi_match_controller(struct device *dev, void *res, void *ctlr)
    -{
    - return *(struct spi_controller **)res == ctlr;
    -}
    -
    static int __unregister(struct device *dev, void *null)
    {
    spi_unregister_device(to_spi_device(dev));
    @@ -2395,8 +2391,7 @@ void spi_unregister_controller(struct spi_controller *ctlr)
    /* Release the last reference on the controller if its driver
    * has not yet been converted to devm_spi_alloc_master/slave().
    */
    - if (!devres_find(ctlr->dev.parent, devm_spi_release_controller,
    - devm_spi_match_controller, ctlr))
    + if (!ctlr->devm_allocated)
    put_device(&ctlr->dev);

    /* free bus id */
    diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
    index 8ceba9b8e51e..16158fe097a8 100644
    --- a/include/linux/spi/spi.h
    +++ b/include/linux/spi/spi.h
    @@ -450,6 +450,9 @@ struct spi_controller {

    #define SPI_MASTER_GPIO_SS BIT(5) /* GPIO CS must select slave */

    + /* flag indicating this is a non-devres managed controller */
    + bool devm_allocated;
    +
    /* flag indicating this is an SPI slave controller */
    bool slave;

    --
    2.30.2


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