linux-ext4 - Re: [PATCH] ext4: verify dirent offset in ext4

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Message-ID: <7debf2e6-0d2d-46bf-b3f8-f24c8e5f41b5@yandex.ru>
Date: Thu, 3 Jul 2025 12:54:06 +0300
From: Dmitry Antipov <dmantipov@...dex.ru>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: Theodore Ts'o <tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca>,
 linux-ext4@...r.kernel.org,
 syzbot+5322c5c260eb44d209ed@...kaller.appspotmail.com
Subject: Re: [PATCH] ext4: verify dirent offset in ext4_readdir()

On 7/2/25 6:23 PM, Darrick J. Wong wrote:

> Why wouldn't you encode this check in __ext4_check_dir_entry and solve
> this problem for all the callsites?

Next thing to try indeed.

BTW, looking through ext4_search_dir(), why the search doesn't
actually start from the specified offset? I.e. shouldn't it be:

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index a178ac229489..8aa0d68dae71 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1461,7 +1461,7 @@ int ext4_search_dir(struct buffer_head *bh, char *search_buf, int buf_size,
         char * dlimit;
         int de_len;

-       de = (struct ext4_dir_entry_2 *)search_buf;
+       de = (struct ext4_dir_entry_2 *)search_buf + offset;
         dlimit = search_buf + buf_size;
         while ((char *) de < dlimit - EXT4_BASE_DIR_LEN) {
                 /* this code is executed quadratically often */

Dmitry