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Subjectre: spi: Add call to spi_slave_abort() function when spidev driver is released
Date
Hi,

Static analysis with Coverity has detected an potential dereference of a
free'd object with commit:

commit 9f918a728cf86b2757b6a7025e1f46824bfe3155
Author: Lukasz Majewski <lukma@denx.de>
Date: Wed Sep 25 11:11:42 2019 +0200

spi: Add call to spi_slave_abort() function when spidev driver is
released

In spidev_release() in drivers/spi/spidev.c the analysis is as follows:

600static int spidev_release(struct inode *inode, struct file *filp)
601{
602 struct spidev_data *spidev;
603
604 mutex_lock(&device_list_lock);

1. alias: Assigning: spidev = filp->private_data. Now both point to
the same storage.

605 spidev = filp->private_data;
606 filp->private_data = NULL;
607
608 /* last close? */
609 spidev->users--;

2. Condition !spidev->users, taking true branch.

610 if (!spidev->users) {
611 int dofree;
612
613 kfree(spidev->tx_buffer);
614 spidev->tx_buffer = NULL;
615
616 kfree(spidev->rx_buffer);
617 spidev->rx_buffer = NULL;
618
619 spin_lock_irq(&spidev->spi_lock);

3. Condition spidev->spi, taking false branch.

620 if (spidev->spi)
621 spidev->speed_hz = spidev->spi->max_speed_hz;
622
623 /* ... after we unbound from the underlying device? */

4. Condition spidev->spi == NULL, taking true branch.

624 dofree = (spidev->spi == NULL);
625 spin_unlock_irq(&spidev->spi_lock);
626

5. Condition dofree, taking true branch.

627 if (dofree)

6. freed_arg: kfree frees spidev.

628 kfree(spidev);
629 }
630#ifdef CONFIG_SPI_SLAVE

CID 89726 (#1 of 1): Read from pointer after free (USE_AFTER_FREE)
7. deref_after_free: Dereferencing freed pointer spidev.

631 spi_slave_abort(spidev->spi);
632#endif
633 mutex_unlock(&device_list_lock);
634
635 return 0;
636}

The call to spi_slave_abort() on spidev is reading an earlier kfree'd
spidev.

Colin

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