Messages in this thread | | | Date | Tue, 7 Apr 2015 11:34:25 +0300 | Subject | Re: [PATCH] lguest: explicitly setup /dev/lguest private_data | From | Daniel Baluta <> |
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On Tue, Apr 7, 2015 at 11:18 AM, Tom Van Braeckel <tomvanbraeckel@gmail.com> wrote: > The private_data member of the /dev/lguest device file is used to hold > the current struct lguest and needs to be set to NULL to signify that > no initialization has taken place. > > We explicitly set it to NULL to be independent of whatever value the > misc subsystem initializes it to. > > Signed-off-by: Tom Van Braeckel <tomvanbraeckel@gmail.com> > --- > Backstory: > ========== > The misc subsystem used to initialize a file's private_data to point to > the misc device when a driver had registered a custom open file > operation and initialized it to NULL when a custom open file operation > had *not* been provided. > > This subtle quirk was confusing, to the point where kernel code > registered *empty* file open operations to have private_data point to > the misc device structure. > > And it lead to bugs, where the addition or removal of a custom open > file operation surprisingly changed the initial contents of a file's > private_data structure. > > The misc subsystem is currently underdoing changes to *always* set > private_data to point to the misc device instead of only doing this > when a custom open file operation has been registered. > > Intel's 0day kernel testing robot discovered that the lguest driver > depended on it implicitly being initialized to NULL, as Fengguang Wu > reported. Thanks a lot for all the hard work! > > drivers/lguest/lguest_user.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/drivers/lguest/lguest_user.c b/drivers/lguest/lguest_user.c > index c4c6113..054bf70 100644 > --- a/drivers/lguest/lguest_user.c > +++ b/drivers/lguest/lguest_user.c > @@ -98,6 +98,17 @@ static int trap(struct lg_cpu *cpu, const unsigned long __user *input) > return 0; > } > > +/* > + * Set up the /dev/lguest file structure > + * The file's private_data will hold the "struct lguest" after > + * initialization and is used to check whether it is already initialized. > + */ > +static int open(struct inode *inode, struct file *file) > +{ > + file->private_data = NULL; > + return 0; > +} > + > /*L:040 > * Once our Guest is initialized, the Launcher makes it run by reading > * from /dev/lguest. > @@ -405,10 +416,11 @@ static int close(struct inode *inode, struct file *file) > * > * We begin our understanding with the Host kernel interface which the Launcher > * uses: reading and writing a character device called /dev/lguest. All the > - * work happens in the read(), write() and close() routines: > + * work happens in the open(), read(), write() and close() routines: > */ > static const struct file_operations lguest_fops = { > .owner = THIS_MODULE, > + .open = open, > .release = close, > .write = write, > .read = read,
Hmm, isn't this already fixed?
https://lkml.org/lkml/2015/3/23/319
thanks, Daniel.
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