This is a note to let you know that I've just added the patch titled propagate_one(): mnt_set_mountpoint() needs mount_lock to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: propagate_one-mnt_set_mountpoint-needs-mount_lock.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From b0d3869ce9eeacbb1bbd541909beeef4126426d5 Mon Sep 17 00:00:00 2001 From: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Date: Mon, 27 Apr 2020 10:26:22 -0400 Subject: propagate_one(): mnt_set_mountpoint() needs mount_lock From: Al Viro <viro@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxx>, 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@xxxxxxxxxx Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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); } Patches currently in stable-queue which might be from viro@xxxxxxxxxxxxxxxxxx are queue-5.4/propagate_one-mnt_set_mountpoint-needs-mount_lock.patch