lkml.org 
[lkml]   [2008]   [Jan]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [patch 5/9] unprivileged mounts: allow unprivileged bind mounts
    From
    Date
    On Tue, 2008-01-08 at 12:35 +0100, Miklos Szeredi wrote:
    > @@ -510,10 +533,16 @@ static struct vfsmount *clone_mnt(struct
    > int flag)
    > {
    > struct super_block *sb = old->mnt_sb;
    > - struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
    > + struct vfsmount *mnt;
    >
    > + if (flag & CL_SETUSER) {
    > + int err = reserve_user_mount();
    > + if (err)
    > + return ERR_PTR(err);
    > + }
    > + mnt = alloc_vfsmnt(old->mnt_devname);
    > if (!mnt)
    > - return ERR_PTR(-ENOMEM);
    > + goto alloc_failed;
    >
    > mnt->mnt_flags = old->mnt_flags;
    > atomic_inc(&sb->s_active);

    I think there's a little race here. We could have several users racing
    to get to this point when nr_user_mounts==max_user_mounts-1. One user
    wins the race and gets their mount reserved. The others get the error
    out of reserve_user_mount(), and return.

    But, the winner goes on to error out on some condition further down in
    clone_mnt() and never actually instantiates the mount.

    Do you think this is a problem?

    I think just about the one solution is to block new mounters on a
    sleepable lock until the race winner actually finishes their mount
    operation.

    -- Dave



    \
     
     \ /
      Last update: 2008-01-08 19:29    [W:5.095 / U:0.472 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site