Hi Viresh, A bit of background: at some point in time, the i2c adapter number (as represented internally by the kernel) could be different from the i2c device node number (as seen by user-space.) I put an end to this madness years ago, but it seems some legacy code from that time survived in i2c-dev.
On Tue, 5 Jul 2016 19:57:06 -0700, Viresh Kumar wrote: > There is no code protecting i2c_dev to be freed after it is returned > from i2c_dev_get_by_minor() and using it to access the value which we > already have (minor) isn't safe really. I agree that i2c_dev_get_by_minor() looks racy by nature. It is possible that i2c_dev_get_by_minor() can be removed altogether. There are 2 other calling locations beyond the one you want to remove. If one can be removed then I suspect others can be removed as well (maybe with some more work though.) If i2c_dev_get_by_minor() needs to stay for whatever reason, then my next worry is that struct i2c_dev carries an unaccounted reference to an i2c_adapter. This looks seriously broken. i2c_dev->adap should only be set on open, and cleared on close. > Avoid using it and get the adapter directly from 'minor'. > > Signed-off-by: Viresh Kumar <[email protected]> > --- > drivers/i2c/i2c-dev.c | 7 +------ > 1 file changed, 1 insertion(+), 6 deletions(-) > > diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c > index 6ecfd76270f2..66f323fd3982 100644 > --- a/drivers/i2c/i2c-dev.c > +++ b/drivers/i2c/i2c-dev.c > @@ -485,13 +485,8 @@ static int i2cdev_open(struct inode *inode, struct file > *file) > unsigned int minor = iminor(inode); > struct i2c_client *client; > struct i2c_adapter *adap; > - struct i2c_dev *i2c_dev; > - > - i2c_dev = i2c_dev_get_by_minor(minor); > - if (!i2c_dev) > - return -ENODEV; > > - adap = i2c_get_adapter(i2c_dev->adap->nr); > + adap = i2c_get_adapter(minor); > if (!adap) > return -ENODEV; > This is the most simple fix to your immediate problem. However it doesn't address the big design issue. -- Jean Delvare SUSE L3 Support
