Have ext2 reject file handles with bad inode numbers early.

[Neil Brown]

From: Neil Brown <neilb@xxxxxxx>

This prevents bad inode numbers from triggering errors in
ext2_get_inode.


Signed-off-by: Neil Brown <neilb@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 fs/ext2/super.c |   41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

--- linux-2.6.17.7.orig/fs/ext2/super.c
+++ linux-2.6.17.7/fs/ext2/super.c
@@ -252,6 +252,46 @@ 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.
@@ -259,6 +299,7 @@ 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)

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