udf: Avoid directory type conversion failure due to ENOMEM

When converting directory from in-ICB to normal format, the last
iteration through the directory fixing up directory enteries can fail
due to ENOMEM. We do not expect this iteration to fail since the
directory is already verified to be correct and it is difficult to undo
the conversion at this point. So just use GFP_NOFAIL to make sure the
small allocation cannot fail.

Reported-by: syzbot+111eaa994ff74f8d440f@syzkaller.appspotmail.com
Fixes: 0aba4860 ("udf: Allocate name buffer in directory iterator on heap")
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/directory.c

@@ -251,9 +251,12 @@ int udf_fiiter_init(struct udf_fileident_iter *iter, struct inode *dir,
 	iter->elen = 0;
 	iter->epos.bh = NULL;
 	iter->name = NULL;
-	iter->namebuf = kmalloc(UDF_NAME_LEN_CS0, GFP_KERNEL);
-	if (!iter->namebuf)
-		return -ENOMEM;
+	/*
+	 * When directory is verified, we don't expect directory iteration to
+	 * fail and it can be difficult to undo without corrupting filesystem.
+	 * So just do not allow memory allocation failures here.
+	 */
+	iter->namebuf = kmalloc(UDF_NAME_LEN_CS0, GFP_KERNEL | __GFP_NOFAIL);
 
 	if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB) {
 		err = udf_copy_fi(iter);