Hi, On Sat, 2018-12-22 at 13:19 +0100, Stefan Wahren wrote: > Hi Paul, > > > Paul Kocialkowski <paul.kocialkow...@bootlin.com> hat am 21. Dezember 2018 > > um 13:11 geschrieben: > > > > > > The driver's interrupt handler checks whether a message is currently > > being handled with the curr_msg pointer. When it is NULL, the interrupt > > is considered to be unexpected. Similarly, the i2c_start_transfer > > routine checks for the remaining number of messages to handle in > > num_msgs. > > > > However, these values are never cleared and always keep the message and > > number relevant to the latest transfer (which might be done already and > > the underlying message memory might have been freed). > > > > When an unexpected interrupt hits with the DONE bit set, the isr will > > then try to access the flags field of the curr_msg structure, leading > > to a fatal page fault. > > > > Fix the issue by systematically clearing curr_msg and num_msgs in the > > driver-wide device structure when a transfer is considered complete. > > > > Signed-off-by: Paul Kocialkowski <paul.kocialkow...@bootlin.com> > > --- > > drivers/i2c/busses/i2c-bcm2835.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/drivers/i2c/busses/i2c-bcm2835.c > > b/drivers/i2c/busses/i2c-bcm2835.c > > index 44deae78913e..5486252f5f2f 100644 > > --- a/drivers/i2c/busses/i2c-bcm2835.c > > +++ b/drivers/i2c/busses/i2c-bcm2835.c > > @@ -298,6 +298,9 @@ static int bcm2835_i2c_xfer(struct i2c_adapter *adap, > > struct i2c_msg msgs[], > > return -ETIMEDOUT; > > } > > > > + i2c_dev->curr_msg = NULL; > > + i2c_dev->num_msgs = 0; > > AFAIU this would reduce the chance of a use-after-free dramatically but not > completely.
Do you have a specific case of use-after-free related to these variables in mind that this cleanup would not fix (except for the timeout case)? The msg_buf element (in association with msg_buf_remaining keeping its previous value) could also lead to similar problems, so I'm thinking of making a bcm2835_i2c_finish_transfer function to group all the cleanups and call that right after wait_for_completion_timeout. > Btw: Why did you leave of the i2c transfer timeout case? I should definitely have included it, actually. Cheers, Paul > Thanks > Stefan > > > + > > if (!i2c_dev->msg_err) > > return num; > > > > -- > > 2.20.1 > > -- Paul Kocialkowski, Bootlin (formerly Free Electrons) Embedded Linux and kernel engineering https://bootlin.com
