git: ecc571a85858 - stable/12 - nullfs: protect against user creating inconsistent state

[Konstantin Belousov]

The branch stable/12 has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=ecc571a858586e7b62cae3794c0f6250a91a483b

commit ecc571a858586e7b62cae3794c0f6250a91a483b
Author:     Konstantin Belousov <kib at FreeBSD.org>
AuthorDate: 2021-04-01 17:42:14 +0000
Commit:     Konstantin Belousov <kib at FreeBSD.org>
CommitDate: 2021-04-09 04:57:37 +0000

    nullfs: protect against user creating inconsistent state
    
    PR:     253593
    
    (cherry picked from commit 76b1b5ce6d81f66b09be8a20aecd064b65fd6b50)
---
 sys/fs/nullfs/null_vnops.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/sys/fs/nullfs/null_vnops.c b/sys/fs/nullfs/null_vnops.c
index b663d8d718d3..62351cd9d832 100644
--- a/sys/fs/nullfs/null_vnops.c
+++ b/sys/fs/nullfs/null_vnops.c
@@ -376,10 +376,21 @@ null_lookup(struct vop_lookup_args *ap)
 	 */
 	ldvp = NULLVPTOLOWERVP(dvp);
 	vp = lvp = NULL;
-	KASSERT((ldvp->v_vflag & VV_ROOT) == 0 ||
-	    ((dvp->v_vflag & VV_ROOT) != 0 && (flags & ISDOTDOT) == 0),
-	    ("ldvp %p fl %#x dvp %p fl %#x flags %#x", ldvp, ldvp->v_vflag,
-	     dvp, dvp->v_vflag, flags));
+
+	/*
+	 * Renames in the lower mounts might create an inconsistent
+	 * configuration where lower vnode is moved out of the
+	 * directory tree remounted by our null mount.  Do not try to
+	 * handle it fancy, just avoid VOP_LOOKUP() with DOTDOT name
+	 * which cannot be handled by VOP, at least passing over lower
+	 * root.
+	 */
+	if ((ldvp->v_vflag & VV_ROOT) != 0 && (flags & ISDOTDOT) != 0) {
+		KASSERT((dvp->v_vflag & VV_ROOT) == 0,
+		    ("ldvp %p fl %#x dvp %p fl %#x flags %#x",
+		    ldvp, ldvp->v_vflag, dvp, dvp->v_vflag, flags));
+		return (ENOENT);
+	}
 
 	/*
 	 * Hold ldvp.  The reference on it, owned by dvp, is lost in