On Tue, Apr 07, 2015 at 10:18:18AM +0200, Tom Van Braeckel 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 <tomvanbraec...@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(-)
I can take this through my char-misc tree, where this misc core change was, if the lguest maintainer (i.e. Rusty) acks it. Tom, thanks for tracking this down. greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
