udf: Verify symlink size before loading it

commit a1d47b26 upstream.

UDF specification allows arbitrarily large symlinks. However we support
only symlinks at most one block large. Check the length of the symlink
so that we don't access memory beyond end of the symlink block.
Reported-by: Carl Henrik Lunde <chlunde@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
[bwh: Backported to 2.6.32: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

CVE-2014-9728
Signed-off-by: Willy Tarreau <w@1wt.eu>

fs/udf/symlink.c

@@ -76,10 +76,16 @@ static int udf_symlink_filler(struct file *file, struct page *page)
 	struct inode *inode = page->mapping->host;
 	struct buffer_head *bh = NULL;
 	char *symlink;
-	int err = -EIO;
+	int err;
 	char *p = kmap(page);
 	struct udf_inode_info *iinfo;
 
+	/* We don't support symlinks longer than one block */
+	if (inode->i_size > inode->i_sb->s_blocksize) {
+		err = -ENAMETOOLONG;
+		goto out_unmap;
+	}
+
 	lock_kernel();
 	iinfo = UDF_I(inode);
 	if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB) {
@@ -87,8 +93,10 @@ static int udf_symlink_filler(struct file *file, struct page *page)
 	} else {
 		bh = sb_bread(inode->i_sb, udf_block_map(inode, 0));
 
-		if (!bh)
-			goto out;
+		if (!bh) {
+			err = -EIO;
+			goto out_unlock_inode;
+		}
 
 		symlink = bh->b_data;
 	}
@@ -102,9 +110,10 @@ static int udf_symlink_filler(struct file *file, struct page *page)
 	unlock_page(page);
 	return 0;
 
-out:
+out_unlock_inode:
 	unlock_kernel();
 	SetPageError(page);
+out_unmap:
 	kunmap(page);
 	unlock_page(page);
 	return err;