Commit 156cacb1 authored Sep 21, 2012 by Al Viro

do_add_mount()/umount -l races



normally we deal with lock_mount()/umount races by checking that
mountpoint to be is still in our namespace after lock_mount() has
been done.  However, do_add_mount() skips that check when called
with MNT_SHRINKABLE in flags (i.e. from finish_automount()).  The
reason is that ->mnt_ns may be a temporary namespace created exactly
to contain automounts a-la NFS4 referral handling.  It's not the
namespace of the caller, though, so check_mnt() would fail here.
We still need to check that ->mnt_ns is non-NULL in that case,
though.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

parent fea7a08a

fs/namespace.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -1886,8 +1886,14 @@ static int do_add_mount(struct mount newmnt, struct path path, int mnt_flags)
		return err;

		err = -EINVAL;
		if (!(mnt_flags & MNT_SHRINKABLE) && !check_mnt(real_mount(path->mnt)))
		if (unlikely(!check_mnt(real_mount(path->mnt)))) {
		/* that's acceptable only for automounts done in private ns */
		if (!(mnt_flags & MNT_SHRINKABLE))
		goto unlock;
		/* ... and for those we'd better have mountpoint still alive */
		if (!real_mount(path->mnt)->mnt_ns)
		goto unlock;
		}

		/* Refuse the same filesystem on the same mount point */
		err = -EBUSY;

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