This fixes a bug in UFS2 exported NFS volumes. An NFS client can

crash a server that has exported UFS2 by presenting a filehandle
with an inode number that references an uninitialized inode in a
cylinder group. The problem is that UFS2 only initializes blocks
of inodes as they are first allocated and ffs_fhtovp() does not
validate that the inode is in a range of inodes that have been
initialized. Attempting to read an uninitialized inode gets random
data from the disk. When the kernel tries to interpret it as an
inode, panics often arise.

Reported by: Christos Zoulas (from NetBSD)
Reviewed by: kib

1 files changed, 28 insertions, 3 deletions

diff --git a/sys/ufs/ffs/ffs_vfsops.c b/sys/ufs/ffs/ffs_vfsops.c
index 82c22fd..a82ef61 100644
--- a/sys/ufs/ffs/ffs_vfsops.c
+++ b/sys/ufs/ffs/ffs_vfsops.c
@@ -1797,6 +1797,7 @@ ffs_vgetf(mp, ino, flags, vpp, ffs_flags)
  *
  * Have to be really careful about stale file handles:
  * - check that the inode number is valid
+ * - for UFS2 check that the inode number is initialized
  * - call ffs_vget() to get the locked inode
  * - check for an unallocated inode (i_mode == 0)
  * - check that the given client host has export rights and return
@@ -1810,13 +1811,37 @@ ffs_fhtovp(mp, fhp, flags, vpp)
 	struct vnode **vpp;
 {
 	struct ufid *ufhp;
+	struct ufsmount *ump;
 	struct fs *fs;
+	struct cg *cgp;
+	struct buf *bp;
+	ino_t ino;
+	u_int cg;
+	int error;
 
 	ufhp = (struct ufid *)fhp;
-	fs = VFSTOUFS(mp)->um_fs;
-	if (ufhp->ufid_ino < ROOTINO ||
-	    ufhp->ufid_ino >= fs->fs_ncg * fs->fs_ipg)
+	ino = ufhp->ufid_ino;
+	ump = VFSTOUFS(mp);
+	fs = ump->um_fs;
+	if (ino < ROOTINO || ino >= fs->fs_ncg * fs->fs_ipg)
 		return (ESTALE);
+	/*
+	 * Need to check if inode is initialized because UFS2 does lazy
+	 * initialization and nfs_fhtovp can offer arbitrary inode numbers.
+	 */
+	if (fs->fs_magic != FS_UFS2_MAGIC)
+		return (ufs_fhtovp(mp, ufhp, flags, vpp));
+	cg = ino_to_cg(fs, ino);
+	error = bread(ump->um_devvp, fsbtodb(fs, cgtod(fs, cg)),
+		(int)fs->fs_cgsize, NOCRED, &bp);
+	if (error)
+		return (error);
+	cgp = (struct cg *)bp->b_data;
+	if (!cg_chkmagic(cgp) || ino >= cg * fs->fs_ipg + cgp->cg_initediblk) {
+		brelse(bp);
+		return (ESTALE);
+	}
+	brelse(bp);
 	return (ufs_fhtovp(mp, ufhp, flags, vpp));
 }