[src/trunk]: src/sys/kern Honor LOCKPARENT for ".." of the root directory.

[chs <chs%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/e97af58caa47
branches:  trunk
changeset: 958260:e97af58caa47
user:      chs <chs%NetBSD.org@localhost>
date:      Tue Dec 29 22:13:40 2020 +0000

description:
Honor LOCKPARENT for ".." of the root directory.

Reported-by: syzbot+f40b9f241b818fd12198%syzkaller.appspotmail.com@localhost

diffstat:

 sys/kern/vfs_lookup.c |  45 ++++++++++++++++++++++++++++++---------------
 1 files changed, 30 insertions(+), 15 deletions(-)

diffs (80 lines):

diff -r 043478fd7a5a -r e97af58caa47 sys/kern/vfs_lookup.c
--- a/sys/kern/vfs_lookup.c     Tue Dec 29 21:32:46 2020 +0000
+++ b/sys/kern/vfs_lookup.c     Tue Dec 29 22:13:40 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_lookup.c,v 1.224 2020/06/15 18:44:10 ad Exp $      */
+/*     $NetBSD: vfs_lookup.c,v 1.225 2020/12/29 22:13:40 chs Exp $     */
 
 /*
  * Copyright (c) 1982, 1986, 1989, 1993
@@ -37,7 +37,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_lookup.c,v 1.224 2020/06/15 18:44:10 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_lookup.c,v 1.225 2020/12/29 22:13:40 chs Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_magiclinks.h"
@@ -1047,6 +1047,28 @@
 }
 
 /*
+ * Determine the desired locking mode for the directory of a lookup.
+ */
+static int
+lookup_lktype(struct vnode *searchdir, struct componentname *cnp)
+{
+
+       /*
+        * If the file system supports VOP_LOOKUP() with a shared lock, and
+        * we are not making any modifications (nameiop LOOKUP) or this is
+        * not the last component then get a shared lock.  Where we can't do
+        * fast-forwarded lookups (for example with layered file systems)
+        * then this is the fallback for reducing lock contention.
+        */
+       if ((searchdir->v_mount->mnt_iflag & IMNT_SHRLOOKUP) != 0 &&
+           (cnp->cn_nameiop == LOOKUP || (cnp->cn_flags & ISLASTCN) == 0)) {
+               return LK_SHARED;
+       } else {
+               return LK_EXCLUSIVE;
+       }
+}
+
+/*
  * Call VOP_LOOKUP for a single lookup; return a new search directory
  * (used when crossing mountpoints up or searching union mounts down) and
  * the found object, which for create operations may be NULL on success.
@@ -1100,6 +1122,11 @@
                                foundobj = searchdir;
                                vref(foundobj);
                                *foundobj_ret = foundobj;
+                               if (cnp->cn_flags & LOCKPARENT) {
+                                       lktype = lookup_lktype(searchdir, cnp);
+                                       vn_lock(searchdir, lktype | LK_RETRY);
+                                       searchdir_locked = true;
+                               }
                                error = 0;
                                goto done;
                        }
@@ -1137,19 +1164,7 @@
                }
        }
 
-       /*
-        * If the file system supports VOP_LOOKUP() with a shared lock, and
-        * we are not making any modifications (nameiop LOOKUP) or this is
-        * not the last component then get a shared lock.  Where we can't do
-        * fast-forwarded lookups (for example with layered file systems)
-        * then this is the fallback for reducing lock contention.
-        */
-       if ((searchdir->v_mount->mnt_iflag & IMNT_SHRLOOKUP) != 0 &&
-           (cnp->cn_nameiop == LOOKUP || (cnp->cn_flags & ISLASTCN) == 0)) {
-               lktype = LK_SHARED;
-       } else {
-               lktype = LK_EXCLUSIVE;
-       }
+       lktype = lookup_lktype(searchdir, cnp);
 
        /*
         * We now have a segment name to search for, and a directory to search.