On Wed, Sep 30, 2015 at 07:42:15PM -0400, Mike Snitzer wrote:
> On Wed, Sep 30 2015 at 4:15pm -0400,
> Seth Forshee <seth.forshee@xxxxxxxxxxxxx> wrote:
>
> > When mounting a filesystem on a block device there is currently
> > no verification that the user has appropriate access to the
> > device file passed to mount. This has not been an issue so far
> > since the user in question has always been root, but this must
> > be changed before allowing unprivileged users to mount in user
> > namespaces.
> >
> > To fix this, add an argument to lookup_bdev() to specify the
> > required permissions. If the mask of permissions is zero, or
> > if the user has CAP_SYS_ADMIN, the permission check is skipped,
> > otherwise the lookup fails if the user does not have the
> > specified access rights for the inode at the supplied path.
> >
> > Callers associated with mounting are updated to pass permission
> > masks to lookup_bdev() so that these mounts will fail for an
> > unprivileged user who lacks permissions for the block device
> > inode. All other callers pass 0 to maintain their current
> > behaviors.
> >
> > Signed-off-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
> > ---
> > drivers/md/bcache/super.c | 2 +-
> > drivers/md/dm-table.c | 2 +-
> > drivers/mtd/mtdsuper.c | 6 +++++-
> > fs/block_dev.c | 18 +++++++++++++++---
> > fs/quota/quota.c | 2 +-
> > include/linux/fs.h | 2 +-
> > 6 files changed, 24 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> > index e76ed003769e..35bb3ea4cbe2 100644
> > --- a/drivers/md/dm-table.c
> > +++ b/drivers/md/dm-table.c
> > @@ -380,7 +380,7 @@ int dm_get_device(struct dm_target *ti, const char *path, fmode_t mode,
> > BUG_ON(!t);
> >
> > /* convert the path to a device */
> > - bdev = lookup_bdev(path);
> > + bdev = lookup_bdev(path, 0);
> > if (IS_ERR(bdev)) {
> > dev = name_to_dev_t(path);
> > if (!dev)
>
> Given dm_get_device() is passed @mode why not have it do something like
> you did in blkdev_get_by_path()? e.g.:
I only dealt with code related to mounting in this patch since that's
what I'm working on. I have it on my TODO list to consider converting
other callers of lookup_bdev. But if you're sure doing so makes sense
for dm_get_device and that it won't cause regressions then I could add a
patch for it.
Thanks,
Seth
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