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propagate_one(): mnt_set_mountpoint() needs mount_lock

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commit b0d3869ce9 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: Piotr Krysiuk <piotras@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Al Viro 2020-04-27 10:26:22 -04:00 committed by Greg Kroah-Hartman
parent 38faccf5f9
commit fa87bf609a
1 changed files with 4 additions and 5 deletions
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9
fs/pnode.c
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@ -266,14 +266,13 @@ static int propagate_one(struct mount *m)
if (IS_ERR(child))
return PTR_ERR(child);
child->mnt.mnt_flags &= ~MNT_LOCKED;
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);
}