From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from canpmsgout07.his.huawei.com (canpmsgout07.his.huawei.com [113.46.200.222]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A000E1B3B19; Fri, 3 Jul 2026 01:47:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.222 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783043260; cv=none; b=elQ/xqeVul7nYJnGVoPrFvOUS6rLbGfI0jqHN5k2x/QuVcJDa3N7yxJ61onQK0rQlilXd/d5cfAB9XGY8xzoan3qjFWPWebvKjzQgKAYwXNgwFe4GTzswx6Z8/72VZXSoiHMGu+4MiW/W9z14YWhRjwR1W/EPS0RJjJ3/oOva/s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783043260; c=relaxed/simple; bh=v+UamTuzXjtOr0hus3aFtm2L3Ga/21EuK4xpWw4Gz4Q=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=f7TlgkD0BEd4Cw7cN+2vvSCIjLpLjp3u+Zk6/1HA1tyImndVyE7mpKy1qB9QLmoIcg2Nkd2LsyGPYmIhjNFKYQD5XJEHXyNdgCdHf+qDH0trT8d/Xb2ImFkptLJEqgiMrZsZkrMBJHz33ZRrxvuCKphb6t1gEoOUbFgE9N4Amuc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b=Mia6CktN; arc=none smtp.client-ip=113.46.200.222 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b="Mia6CktN" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=8k/TIiob6TPAJ3R5tWfXTy75thoT/sAIuUyb8Gygxzk=; b=Mia6CktNtDlZTdf8mPHBMvK4CFX6W9up3CSM1KfnIw6BTGz7Izmwr6lq3Cx45W4T1icEvmt42 w5wezHw/jVx/rtx7jnQQoOtd+Fdb65kyPpJ+BZFeHc/qBskzxH1+fpZjiVbb9uwY8Nv5QXcOScs 1UkhJcOnwBAS5z0SYDAb+TY= Received: from mail.maildlp.com (unknown [172.19.163.200]) by canpmsgout07.his.huawei.com (SkyGuard) with ESMTPS id 4grwtt5qBhzLm1B; Fri, 3 Jul 2026 09:21:10 +0800 (CST) Received: from dggpemr500006.china.huawei.com (unknown [7.185.36.185]) by mail.maildlp.com (Postfix) with ESMTPS id 8B2FC40572; Fri, 3 Jul 2026 09:30:21 +0800 (CST) Received: from localhost.localdomain (10.50.85.180) by dggpemr500006.china.huawei.com (7.185.36.185) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Fri, 3 Jul 2026 09:30:20 +0800 From: Yao Kai To: , CC: , , , , , , , , , Yao Kai , Subject: [PATCH] ext4: validate readdir offset before accessing dirent Date: Fri, 3 Jul 2026 09:51:06 +0800 Message-ID: <20260703015106.3570064-1-yaokai34@huawei.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: kwepems500001.china.huawei.com (7.221.188.70) To dggpemr500006.china.huawei.com (7.185.36.185) A corrupted directory can trigger the following KASAN report when ext4_readdir() resumes from an invalid position: BUG: KASAN: use-after-free in __ext4_check_dir_entry+0x5ef/0x820 Read of size 2 at addr ffff88810a646000 by task repro_linear/509 Call Trace: dump_stack_lvl+0x53/0x70 print_report+0xd0/0x630 kasan_report+0xce/0x100 __ext4_check_dir_entry+0x5ef/0x820 ext4_readdir+0xcde/0x2b70 iterate_dir+0x1a1/0x520 __x64_sys_getdents64+0x12b/0x220 do_syscall_64+0xf9/0x540 entry_SYSCALL_64_after_hwframe+0x77/0x7f KASAN reports use-after-free because the out-of-bounds access lands in an adjacent freed page. The directory buffer itself is still referenced. ext4_dir_llseek() invalidates the directory cookie so that ext4_readdir() rescans directory entries from the start of the block. The rescan checks only the lower bound of rec_len before advancing. A corrupted rec_len can therefore place the offset where the block has insufficient space for a complete directory entry. The rescan itself may dereference that truncated entry, or the main loop may pass it to __ext4_check_dir_entry(). The latter reads de->rec_len before validating the range. For example: block offset 0 4092 4096 |---- de1.rec_len = 4092 -----|----| de2.inode | de2.rec_len ^ OOB, reported as UAF de2 starts at offset 4092 in this 4 KiB block. Its four-byte inode fits in the block, but its rec_len starts at offset 4096 and crosses the boundary. The minimum safe length is inode-dependent. Encrypted and casefolded directory entries need eight additional hash bytes, while a valid metadata checksum tail is only 12 bytes. Cache the metadata checksum feature state and derive the minimum directory entry length from the on-disk format. Use it to bound both the rescan and the offset passed to the main loop. Report an offset in a truncated block tail and skip the remainder of the block, while continuing to accept an offset exactly at the block boundary. Reported-by: syzbot+5322c5c260eb44d209ed@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=5322c5c260eb44d209ed Fixes: ac27a0ec112a ("[PATCH] ext4: initial copy of files from ext3") Signed-off-by: Yao Kai --- fs/ext4/dir.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c index 17edd678fa87..5c943d18882a 100644 --- a/fs/ext4/dir.c +++ b/fs/ext4/dir.c @@ -138,6 +138,7 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx) struct buffer_head *bh = NULL; struct fscrypt_str fstr = FSTR_INIT(NULL, 0); struct dir_private_info *info = file->private_data; + bool has_csum = ext4_has_feature_metadata_csum(sb); err = fscrypt_prepare_readdir(inode); if (err) @@ -149,7 +150,7 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx) return err; /* Can we just clear INDEX flag to ignore htree information? */ - if (!ext4_has_feature_metadata_csum(sb)) { + if (!has_csum) { /* * We don't set the inode dirty flag since it's not * critical that it gets flushed back to the disk. @@ -235,7 +236,10 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx) * dirent right now. Scan from the start of the block * to make sure. */ if (!inode_eq_iversion(inode, info->cookie)) { - for (i = 0; i < sb->s_blocksize && i < offset; ) { + for (i = 0; + i <= sb->s_blocksize - + ext4_dir_rec_len(1, has_csum ? NULL : inode) && + i < offset;) { de = (struct ext4_dir_entry_2 *) (bh->b_data + i); /* It's too expensive to do a full @@ -257,6 +261,17 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx) info->cookie = inode_query_iversion(inode); } + if (unlikely(offset < sb->s_blocksize && + offset > sb->s_blocksize - + ext4_dir_rec_len(1, has_csum ? NULL : inode))) { + EXT4_ERROR_FILE(file, bh->b_blocknr, + "bad entry in directory: %s - offset=%u, size=%lu", + "directory entry too close to block end", + offset, sb->s_blocksize); + ctx->pos = (ctx->pos | (sb->s_blocksize - 1)) + 1; + goto next_block; + } + while (ctx->pos < inode->i_size && offset < sb->s_blocksize) { de = (struct ext4_dir_entry_2 *) (bh->b_data + offset); @@ -312,6 +327,7 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx) ctx->pos += ext4_rec_len_from_disk(de->rec_len, sb->s_blocksize); } +next_block: if ((ctx->pos < inode->i_size) && !dir_relax_shared(inode)) goto done; brelse(bh); -- 2.43.0