Hi Lukasz, On Thu, Sep 26, 2019 at 12:14 PM Lukasz Majewski <lu...@denx.de> wrote: > > Static analysis with Coverity has detected an potential dereference > > of a free'd object with commit: > > > > commit 9f918a728cf86b2757b6a7025e1f46824bfe3155 > > Author: Lukasz Majewski <lu...@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. > > Thanks for spotting this issue - indeed there is a possibility to use > spidev after being kfree'd.
Worse, this makes me realize spidev->spi may be a NULL pointer, which will be dereferenced by spi_slave_abort(), so caching it before the call to kfree() won't work. > However, Geert (CC'ed) had some questions about placement of this > function call, so I will wait with providing fix until he replies. Seems like this needs more thought... Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds