From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 2220441BA94; Sat, 12 Sep 2026 10:13:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789208016; cv=none; b=tdsoCFIlmmwySUjGv2Za8Dbr31O9raxX++UT4mwp8ahFEpsIwHZDcJ2tvKXh+dXs40JAvaRJVzf320a7zlIkeI3tGLG2a+14Db1xNd7hOuCB8DbnXNmSrPSvC03gP/N5mMZPs3z1GnAelJ7Q6gvpu2XaQoWyoSbG3kvbFyQoRVA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789208016; c=relaxed/simple; bh=Pw/Wx8zk96vLveXQmLpP4YVmzwXM1L8koihlc7+kXfs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=PyD0cde6PHQ2SIAQcmvBKJYqtKe8JgtQQQPBpRNy3Awa5SOkGYnsqxErIVlTeCSa6vTsy8kWJvROdmImkgCPPqtS3epauKr7eyH8MeTJ7ghZ7i/hp7bhvk4RM1HRKU9Bj7hcGO3b0zVLXNs7qnFOt/jdN7G17wbdb2HIsMWBGn0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=xkl/V3DX; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="xkl/V3DX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0DEC01F000FF; Sat, 12 Sep 2026 10:13:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789208015; bh=hzX1Q4T7XxFLuPxBvzg8abEku/c1XBZ9v2kK2fkZIqw=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=xkl/V3DXgu5AIBlaT7dYNzXXbGLOhUYjfOOhKgnFK88wp0QgZvA305s/SxPSPsigk VYZQjYmgUf564lJoeCpG2CUaAC6rEvvyZyh/LuSXFtn5KQ+jXaKs+JPIwC7xjbn+RW ONeMbjwdxr1vT6fkOPM+/pqs5qHI/x14h8hzF9jA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+5322c5c260eb44d209ed@syzkaller.appspotmail.com, Yao Kai , Zhihao Cheng , Jan Kara , Zhang Yi , Theodore Tso , Sasha Levin Subject: [PATCH 6.18 0531/1518] ext4: validate readdir offset before accessing dirent Date: Sat, 12 Sep 2026 08:45:00 +0200 Message-ID: <20260912065635.457040201@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065623.398859879@linuxfoundation.org> References: <20260912065623.398859879@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yao Kai [ Upstream commit bc4b7b0414c33b2c8898eb04386df0d21a13dad8 ] 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 Reviewed-by: Zhihao Cheng Reviewed-by: Jan Kara Reviewed-by: Zhang Yi Link: https://patch.msgid.link/20260706041313.708346-1-yaokai34@huawei.com Signed-off-by: Theodore Ts'o Signed-off-by: Sasha Levin --- 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 d4164c507a907..290a9aeac15f1 100644 --- a/fs/ext4/dir.c +++ b/fs/ext4/dir.c @@ -137,6 +137,7 @@ 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) @@ -148,7 +149,7 @@ 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. @@ -234,7 +235,10 @@ 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 @@ -256,6 +260,17 @@ 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 = round_up(ctx->pos, sb->s_blocksize); + goto next_block; + } + while (ctx->pos < inode->i_size && offset < sb->s_blocksize) { de = (struct ext4_dir_entry_2 *) (bh->b_data + offset); @@ -311,6 +326,7 @@ 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); -- 2.53.0