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Date: Tue, 7 Apr 2015 10:55:44 +0200 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: Daniel Baluta <daniel.baluta@...el.com> Cc: Tom Van Braeckel <tomvanbraeckel@...il.com>, Rusty Russell <rusty@...tcorp.com.au>, lguest <lguest@...ts.ozlabs.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, kbuild test robot <fengguang.wu@...el.com>, lkp@...org Subject: Re: [PATCH] lguest: explicitly setup /dev/lguest private_data On Tue, Apr 07, 2015 at 11:34:25AM +0300, Daniel Baluta wrote: > On Tue, Apr 7, 2015 at 11:18 AM, Tom Van Braeckel > <tomvanbraeckel@...il.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@...il.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 Ah, this might be a cross-tree issue then, the 0-day bot tested my tree without this change in it, and hit the problem. So all is good when we merge with Linus for 4.1-rc1. But to be "safe" I could queue this up to my tree as well, any objection to that? thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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