knfsd: Don't allow bad file handles to cause extX to go readonly

diff .prev/fs/ext2/super.c ./fs/ext2/super.c
@@ -251,6 +251,46 @@ static struct super_operations ext2_sops
 #endif
 };
 
+static struct dentry *ext2_get_dentry(struct super_block *sb, void *vobjp)
+{
+	__u32 *objp = vobjp;
+	unsigned long ino = objp[0];
+	__u32 generation = objp[1];
+	struct inode *inode;
+	struct dentry *result;
+
+	if (ino != EXT2_ROOT_INO && ino < EXT2_FIRST_INO(sb))
+		return ERR_PTR(-ESTALE);
+	if (ino > le32_to_cpu(EXT2_SB(sb)->s_es->s_inodes_count))
+		return ERR_PTR(-ESTALE);
+
+	/* iget isn't really right if the inode is currently unallocated!!
+	 * ext2_read_inode currently does appropriate checks, but
+	 * it might be "neater" to call ext2_get_inode first and check
+	 * if the inode is valid.....
+	 */
+	inode = iget(sb, ino);
+	if (inode == NULL)
+		return ERR_PTR(-ENOMEM);
+	if (is_bad_inode(inode)
+	    || (generation && inode->i_generation != generation)
+		) {
+		/* we didn't find the right inode.. */
+		iput(inode);
+		return ERR_PTR(-ESTALE);
+	}
+	/* now to find a dentry.
+	 * If possible, get a well-connected one
+	 */
+	result = d_alloc_anon(inode);
+	if (!result) {
+		iput(inode);
+		return ERR_PTR(-ENOMEM);
+	}
+	return result;
+}
+
+
 /* Yes, most of these are left as NULL!!
  * A NULL value implies the default, which works with ext2-like file
  * systems, but can be improved upon.

@@ -258,6 +298,7 @@ static struct super_operations ext2_sops
  */
 static struct export_operations ext2_export_ops = {
 	.get_parent = ext2_get_parent,
+	.get_dentry = ext2_get_dentry,
 };
 
 static unsigned long get_sb_block(void **data)

diff .prev/fs/ext3/super.c ./fs/ext3/super.c
@@ -554,6 +554,48 @@ static int ext3_show_options(struct seq_
 	return 0;
 }
 
+
+static struct dentry *ext3_get_dentry(struct super_block *sb, void *vobjp)
+{
+	__u32 *objp = vobjp;
+	unsigned long ino = objp[0];
+	__u32 generation = objp[1];
+	struct inode *inode;
+	struct dentry *result;
+
+	if (ino != EXT3_ROOT_INO && ino < EXT3_FIRST_INO(sb))
+		return ERR_PTR(-ESTALE);
+	if (ino > le32_to_cpu(EXT3_SB(sb)->s_es->s_inodes_count))
+		return ERR_PTR(-ESTALE);
+
+	/* iget isn't really right if the inode is currently unallocated!!
+	 *
+	 * ext3_read_inode will return a bad_inode if the inode had been deleted.
+	 * so we should be safe.
+	 *
+	 * Currently we don't know the generation for parent directory, so
+	 * a generation of 0 means "accept any"
+	 */
+	inode = iget(sb, ino);
+	if (inode == NULL)
+		return ERR_PTR(-ENOMEM);
+	if (is_bad_inode(inode)
+	    || (generation && inode->i_generation != generation)
+		) {
+		iput(inode);
+		return ERR_PTR(-ESTALE);
+	}
+	/* now to find a dentry.
+	 * If possible, get a well-connected one
+	 */
+	result = d_alloc_anon(inode);
+	if (!result) {
+		iput(inode);
+		return ERR_PTR(-ENOMEM);
+	}
+	return result;
+}
+
 #ifdef CONFIG_QUOTA
 #define QTYPE2NAME(t) ((t)==USRQUOTA?"user":"group")
 #define QTYPE2MOPT(on, t) ((t)==USRQUOTA?((on)##USRJQUOTA):((on)##GRPJQUOTA))

@@ -622,6 +664,7 @@ static struct super_operations ext3_sops
 
 static struct export_operations ext3_export_ops = {
 	.get_parent = ext3_get_parent,
+	.get_dentry = ext3_get_dentry,
 };
 
 enum {