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    Subject[PATCH 5.4 12/83] propagate_one(): mnt_set_mountpoint() needs mount_lock
    Date
    From: Al Viro <viro@zeniv.linux.org.uk>

    commit b0d3869ce9eeacbb1bbd541909beeef4126426d5 upstream.

    ... to protect the modification of mp->m_count done by it. Most of
    the places that modify that thing also have namespace_lock held,
    but not all of them can do so, so we really need mount_lock here.
    Kudos to Piotr Krysiuk <piotras@gmail.com>, who'd spotted a related
    bug in pivot_root(2) (fixed unnoticed in 5.3); search for other
    similar turds has caught out this one.

    Cc: stable@kernel.org
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/pnode.c | 9 ++++-----
    1 file changed, 4 insertions(+), 5 deletions(-)

    --- a/fs/pnode.c
    +++ b/fs/pnode.c
    @@ -261,14 +261,13 @@ static int propagate_one(struct mount *m
    child = copy_tree(last_source, last_source->mnt.mnt_root, type);
    if (IS_ERR(child))
    return PTR_ERR(child);
    + read_seqlock_excl(&mount_lock);
    mnt_set_mountpoint(m, mp, child);
    + if (m->mnt_master != dest_master)
    + SET_MNT_MARK(m->mnt_master);
    + read_sequnlock_excl(&mount_lock);
    last_dest = m;
    last_source = child;
    - if (m->mnt_master != dest_master) {
    - read_seqlock_excl(&mount_lock);
    - SET_MNT_MARK(m->mnt_master);
    - read_sequnlock_excl(&mount_lock);
    - }
    hlist_add_head(&child->mnt_hash, list);
    return count_mounts(m->mnt_ns, child);
    }

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