Stefan Wahren <stefan.wahren@xxxxxxxx> writes: > 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 We don't share I2C buses with VC4, though, right? That would just be totally broken.
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