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    Subject[PATCH 3.12 064/104] mnt: Move the test for MNT_LOCK_READONLY from change_mount_flags into do_remount
    Date
    From: "Eric W. Biederman" <ebiederm@xmission.com>

    3.12-stable review patch. If anyone has any objections, please let me know.

    ===============

    commit 07b645589dcda8b7a5249e096fece2a67556f0f4 upstream.

    There are no races as locked mount flags are guaranteed to never change.

    Moving the test into do_remount makes it more visible, and ensures all
    filesystem remounts pass the MNT_LOCK_READONLY permission check. This
    second case is not an issue today as filesystem remounts are guarded
    by capable(CAP_DAC_ADMIN) and thus will always fail in less privileged
    mount namespaces, but it could become an issue in the future.

    Cc: stable@vger.kernel.org
    Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
    Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    ---
    fs/namespace.c | 13 ++++++++++---
    1 file changed, 10 insertions(+), 3 deletions(-)

    diff --git a/fs/namespace.c b/fs/namespace.c
    index 34fa7a52f373..8e90b037b706 100644
    --- a/fs/namespace.c
    +++ b/fs/namespace.c
    @@ -1806,9 +1806,6 @@ static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
    if (readonly_request == __mnt_is_readonly(mnt))
    return 0;

    - if (mnt->mnt_flags & MNT_LOCK_READONLY)
    - return -EPERM;
    -
    if (readonly_request)
    error = mnt_make_readonly(real_mount(mnt));
    else
    @@ -1834,6 +1831,16 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
    if (path->dentry != path->mnt->mnt_root)
    return -EINVAL;

    + /* Don't allow changing of locked mnt flags.
    + *
    + * No locks need to be held here while testing the various
    + * MNT_LOCK flags because those flags can never be cleared
    + * once they are set.
    + */
    + if ((mnt->mnt.mnt_flags & MNT_LOCK_READONLY) &&
    + !(mnt_flags & MNT_READONLY)) {
    + return -EPERM;
    + }
    err = security_sb_remount(sb, data);
    if (err)
    return err;
    --
    2.0.4


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