svn commit: r326851 - head/sys/fs/devfs

[Konstantin Belousov]

Author: kib
Date: Thu Dec 14 13:41:11 2017
New Revision: 326851
URL: https://svnweb.freebsd.org/changeset/base/326851

Log:
  In devfs_lookupx() dotdot lookup case, avoid dereferencing
  dvp->v_mount after dvp is unlocked.
  
  The vnode might be reclaimed after unlock, so v_mount becomes NULL.
  Cache the struct mount pointer before the unlock, the struct is
  type-stable.
  
  Note that devfs_allocv() reads mp->mnt_data but does not operate on it
  further when dirent is doomed.  The unmount cannot proceed until all
  dirents are reclaimed.
  
  Reported and tested by:	pho
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week

Modified:
  head/sys/fs/devfs/devfs_vnops.c

Modified: head/sys/fs/devfs/devfs_vnops.c
==============================================================================
--- head/sys/fs/devfs/devfs_vnops.c	Thu Dec 14 13:19:43 2017	(r326850)
+++ head/sys/fs/devfs/devfs_vnops.c	Thu Dec 14 13:41:11 2017	(r326851)
@@ -896,6 +896,7 @@ devfs_lookupx(struct vop_lookup_args *ap, int *dm_unlo
 	struct devfs_dirent *de, *dd;
 	struct devfs_dirent **dde;
 	struct devfs_mount *dmp;
+	struct mount *mp;
 	struct cdev *cdev;
 	int error, flags, nameiop, dvplocked;
 	char specname[SPECNAMELEN + 1], *pname;
@@ -907,7 +908,8 @@ devfs_lookupx(struct vop_lookup_args *ap, int *dm_unlo
 	td = cnp->cn_thread;
 	flags = cnp->cn_flags;
 	nameiop = cnp->cn_nameiop;
-	dmp = VFSTODEVFS(dvp->v_mount);
+	mp = dvp->v_mount;
+	dmp = VFSTODEVFS(mp);
 	dd = dvp->v_data;
 	*vpp = NULLVP;
 
@@ -940,8 +942,8 @@ devfs_lookupx(struct vop_lookup_args *ap, int *dm_unlo
 			return (ENOENT);
 		dvplocked = VOP_ISLOCKED(dvp);
 		VOP_UNLOCK(dvp, 0);
-		error = devfs_allocv(de, dvp->v_mount,
-		    cnp->cn_lkflags & LK_TYPE_MASK, vpp);
+		error = devfs_allocv(de, mp, cnp->cn_lkflags & LK_TYPE_MASK,
+		    vpp);
 		*dm_unlock = 0;
 		vn_lock(dvp, dvplocked | LK_RETRY);
 		return (error);
@@ -1026,8 +1028,7 @@ devfs_lookupx(struct vop_lookup_args *ap, int *dm_unlo
 			return (0);
 		}
 	}
-	error = devfs_allocv(de, dvp->v_mount, cnp->cn_lkflags & LK_TYPE_MASK,
-	    vpp);
+	error = devfs_allocv(de, mp, cnp->cn_lkflags & LK_TYPE_MASK, vpp);
 	*dm_unlock = 0;
 	return (error);
 }