Hi Paul, > Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx> hat am 24. Dezember 2018 um 10:10 geschrieben: > > > Hi, > > On Sat, 2018-12-22 at 13:19 +0100, Stefan Wahren wrote: > > Hi Paul, > > > > > Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx> 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.kocialkowski@xxxxxxxxxxx> > > > --- > > > 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)? okay i was wrong about the use-after-free. But i'm not sure about this scenario on the I2C bus shared with the VC4: 1. ARM core starts I2C transfer (bcm2835_i2c_start_transfer) 2. VC4 triggers a BCM2835_I2C_S_DONE interrupt 3. ARM core catches this interrupt before the VC4 Stefan > > 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 >
