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    Subject[PATCH 6.0 834/862] fsi: occ: Prevent use after free
    Date
    From: Eddie James <eajames@linux.ibm.com>

    [ Upstream commit d3e1e24604031b0d83b6c2d38f54eeea265cfcc0 ]

    Use get_device and put_device in the open and close functions to
    make sure the device doesn't get freed while a file descriptor is
    open.
    Also, lock around the freeing of the device buffer and check the
    buffer before using it in the submit function.

    Signed-off-by: Eddie James <eajames@linux.ibm.com>
    Reviewed-by: Guenter Roeck <linux@roeck-us.net>
    Link: https://lore.kernel.org/r/20220513194424.53468-1-eajames@linux.ibm.com
    Signed-off-by: Joel Stanley <joel@jms.id.au>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/fsi/fsi-occ.c | 18 +++++++++++++++---
    1 file changed, 15 insertions(+), 3 deletions(-)

    diff --git a/drivers/fsi/fsi-occ.c b/drivers/fsi/fsi-occ.c
    index c9cc75fbdfb9..28c176d038a2 100644
    --- a/drivers/fsi/fsi-occ.c
    +++ b/drivers/fsi/fsi-occ.c
    @@ -94,6 +94,7 @@ static int occ_open(struct inode *inode, struct file *file)
    client->occ = occ;
    mutex_init(&client->lock);
    file->private_data = client;
    + get_device(occ->dev);

    /* We allocate a 1-page buffer, make sure it all fits */
    BUILD_BUG_ON((OCC_CMD_DATA_BYTES + 3) > PAGE_SIZE);
    @@ -197,6 +198,7 @@ static int occ_release(struct inode *inode, struct file *file)
    {
    struct occ_client *client = file->private_data;

    + put_device(client->occ->dev);
    free_page((unsigned long)client->buffer);
    kfree(client);

    @@ -493,12 +495,19 @@ int fsi_occ_submit(struct device *dev, const void *request, size_t req_len,
    for (i = 1; i < req_len - 2; ++i)
    checksum += byte_request[i];

    - mutex_lock(&occ->occ_lock);
    + rc = mutex_lock_interruptible(&occ->occ_lock);
    + if (rc)
    + return rc;

    occ->client_buffer = response;
    occ->client_buffer_size = user_resp_len;
    occ->client_response_size = 0;

    + if (!occ->buffer) {
    + rc = -ENOENT;
    + goto done;
    + }
    +
    /*
    * Get a sequence number and update the counter. Avoid a sequence
    * number of 0 which would pass the response check below even if the
    @@ -671,10 +680,13 @@ static int occ_remove(struct platform_device *pdev)
    {
    struct occ *occ = platform_get_drvdata(pdev);

    - kvfree(occ->buffer);
    -
    misc_deregister(&occ->mdev);

    + mutex_lock(&occ->occ_lock);
    + kvfree(occ->buffer);
    + occ->buffer = NULL;
    + mutex_unlock(&occ->occ_lock);
    +
    device_for_each_child(&pdev->dev, NULL, occ_unregister_child);

    ida_simple_remove(&occ_ida, occ->idx);
    --
    2.35.1


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