Messages in this thread | | | Date | Sat, 11 Aug 2007 04:47:21 +0100 | From | Christoph Hellwig <> | Subject | Re: [PATCH 3/20] Introduce MS_KERNMOUNT flag |
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On Fri, Aug 10, 2007 at 03:47:55PM +0400, xemul@openvz.org wrote: > This flag tells the .get_sb callback that this is a kern_mount() call > so that it can trust *data pointer to be valid in-kernel one. If this > flag is passed from the user process, it is cleared since the *data > pointer is not a valid kernel object. > > Running a few steps forward - this will be needed for proc to create the > superblock and store a valid pid namespace on it during the namespace > creation. The reason, why the namespace cannot live without proc mount > is described in the appropriate patch.
I don't like this at all. We should never pass kernel and userspace addresses through the same pointer. Maybe add an additional argument to the get_sb prototype instead. But this whole idea of mounting /proc from kernelspace sounds like a really bad idea to me. /proc should never be mounted from the kernel but always normally from userspace.
> > Signed-off-by: Pavel Emelyanov <xemul@openvz.org> > Cc: Oleg Nesterov <oleg@tv-sign.ru> > > --- > > fs/namespace.c | 3 ++- > fs/super.c | 6 +++--- > include/linux/fs.h | 4 +++- > 3 files changed, 8 insertions(+), 5 deletions(-) > > diff -upr linux-2.6.23-rc1-mm1.orig/fs/namespace.c linux-2.6.23-rc1-mm1-7/fs/namespace.c > --- linux-2.6.23-rc1-mm1.orig/fs/namespace.c 2007-07-26 16:34:45.000000000 +0400 > +++ linux-2.6.23-rc1-mm1-7/fs/namespace.c 2007-07-26 16:36:36.000000000 +0400 > @@ -1579,7 +1579,8 @@ long do_mount(char *dev_name, char *dir_ > mnt_flags |= MNT_NOMNT; > > flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | > - MS_NOATIME | MS_NODIRATIME | MS_RELATIME | MS_NOMNT); > + MS_NOATIME | MS_NODIRATIME | MS_RELATIME | > + MS_NOMNT | MS_KERNMOUNT); > > /* ... and get the mountpoint */ > retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd); > diff -upr linux-2.6.23-rc1-mm1.orig/fs/super.c linux-2.6.23-rc1-mm1-7/fs/super.c > --- linux-2.6.23-rc1-mm1.orig/fs/super.c 2007-07-26 16:34:45.000000000 +0400 > +++ linux-2.6.23-rc1-mm1-7/fs/super.c 2007-07-26 16:36:36.000000000 +0400 > @@ -944,9 +944,9 @@ do_kern_mount(const char *fstype, int fl > return mnt; > } > > -struct vfsmount *kern_mount(struct file_system_type *type) > +struct vfsmount *kern_mount_data(struct file_system_type *type, void *data) > { > - return vfs_kern_mount(type, 0, type->name, NULL); > + return vfs_kern_mount(type, MS_KERNMOUNT, type->name, data); > } > > -EXPORT_SYMBOL(kern_mount); > +EXPORT_SYMBOL_GPL(kern_mount_data); > diff -upr linux-2.6.23-rc1-mm1.orig/include/linux/fs.h linux-2.6.23-rc1-mm1-7/include/linux/fs.h > --- linux-2.6.23-rc1-mm1.orig/include/linux/fs.h 2007-07-26 16:34:45.000000000 +0400 > +++ linux-2.6.23-rc1-mm1-7/include/linux/fs.h 2007-07-26 16:36:36.000000000 +0400 > @@ -129,6 +129,7 @@ extern int dir_notify_enable; > #define MS_RELATIME (1<<21) /* Update atime relative to mtime/ctime. */ > #define MS_SETUSER (1<<23) /* set mnt_uid to current user */ > #define MS_NOMNT (1<<24) /* don't allow unprivileged submounts */ > +#define MS_KERNMOUNT (1<<25) /* this is a kern_mount call */ > #define MS_ACTIVE (1<<30) > #define MS_NOUSER (1<<31) > > @@ -1459,7 +1460,8 @@ void unnamed_dev_init(void); > > extern int register_filesystem(struct file_system_type *); > extern int unregister_filesystem(struct file_system_type *); > -extern struct vfsmount *kern_mount(struct file_system_type *); > +extern struct vfsmount *kern_mount_data(struct file_system_type *, void *data); > +#define kern_mount(type) kern_mount_data(type, NULL) > extern int may_umount_tree(struct vfsmount *); > extern int may_umount(struct vfsmount *); > extern void umount_tree(struct vfsmount *, int, struct list_head *); > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ ---end quoted text--- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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