4.19-stable review patch. If anyone has any objections, please let me know.
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From: Benjamin Coddington bcodding@redhat.com
commit 1e9c75fb9c47a75a9aec0cd17db5f6dc36b58e00 upstream.
Since commit ff17fa561a04 ("d_invalidate(): unhash immediately") immediately unhashes the dentry, we'll never return the mountpoint in lookup_mountpoint(), which can lead to an unbreakable loop in d_invalidate().
I have reports of NFS clients getting into this condition after the server removes an export of an existing mount created through follow_automount(), but I suspect there are various other ways to produce this problem if we hunt down users of d_invalidate(). For example, it is possible to get into this state by using XFS' d_invalidate() call in xfs_vn_unlink():
truncate -s 100m img{1,2}
mkfs.xfs -q -n version=ci img1 mkfs.xfs -q -n version=ci img2
mkdir -p /mnt/xfs mount img1 /mnt/xfs
mkdir /mnt/xfs/sub1 mount img2 /mnt/xfs/sub1
cat > /mnt/xfs/sub1/foo & umount -l /mnt/xfs/sub1 mount img2 /mnt/xfs/sub1
mount --make-private /mnt/xfs
mkdir /mnt/xfs/sub2 mount --move /mnt/xfs/sub1 /mnt/xfs/sub2 rmdir /mnt/xfs/sub1
Fix this by moving the check for an unlinked dentry out of the detach_mounts() path.
Fixes: ff17fa561a04 ("d_invalidate(): unhash immediately") Cc: stable@vger.kernel.org Reviewed-by: "Eric W. Biederman" ebiederm@xmission.com Signed-off-by: Benjamin Coddington bcodding@redhat.com Signed-off-by: Eric W. Biederman ebiederm@xmission.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/namespace.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- a/fs/namespace.c +++ b/fs/namespace.c @@ -695,9 +695,6 @@ static struct mountpoint *lookup_mountpo
hlist_for_each_entry(mp, chain, m_hash) { if (mp->m_dentry == dentry) { - /* might be worth a WARN_ON() */ - if (d_unlinked(dentry)) - return ERR_PTR(-ENOENT); mp->m_count++; return mp; } @@ -711,6 +708,9 @@ static struct mountpoint *get_mountpoint int ret;
if (d_mountpoint(dentry)) { + /* might be worth a WARN_ON() */ + if (d_unlinked(dentry)) + return ERR_PTR(-ENOENT); mountpoint: read_seqlock_excl(&mount_lock); mp = lookup_mountpoint(dentry);