From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793148171; b=UDtPwU8NthbACTzjzHIXex1PtoVqJrTQwSPkebjzUrybM7VaIiuugTdY6p1N6YoFEmLS C2n/LVMNlBX/QjQ5L6cl2SMMFA1xNPDyyjiE81rBl58qD1Q+obZOMqUwQ2Wk1wVw9zJ86 gl4bimD0dpeEZSAUgGnhuXRPTQIxbeVIIxZRL5JUdwqrJmvswXpJ86SUkTdF9sqOqnZFy 4QovnET6dKWwN0yT2RSdZEBNw7+nZHRbXD48RMgvnCok4PrEbbjx74dvwUhovggN82KNv ra9s2wdnGGmRDE7WY5nnUmsX39U+f//SkM4ztiV++5Ah+z8KSVuq1aMF10jHxofo4/Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793148171; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Transfer-Encoding; bh=7ra5EUja+O5y/IsXXX4ZxR+ZhvfGdXSGA1iSsADUCFI=; b=24Hk9AjhK6VQacwiHsWPN/wN4SOKLljoIdoKOHF2osBTn7IGdDwAv6y5AYD23TDpXvEM 4FzPDrw9jnUEsUtfoZamrVvKE421MEE8DrFPkmN6jI1Zgh+cKwN9o6D+vMBTu2T3xYEvz BxjRInBgvrPKfg/CvVlRQfqOIYyvUAdGaoX6X/d+bglJUCvw7Ej6Q1VnumNohR2jfc4j2 nA9YWKnF27GqAyjOYz6u7DOfFdNvxFB4HQrN/KAGDBFQjFOaZn+BFAxgfIPbBCNiVIrPi MbYJESZ/3vQFmBArZm9KItQpZfdBa1gqWKwpF5WnzNSwNFGOJxbnL6gP9mdZx5uyMiA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=d+AytK0O; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 43EB9606A31A; Wed, 28 Oct 2026 00:42:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=d+AytK0O Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9FB5C1F01829; Wed, 28 Oct 2026 00:42:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793148170; bh=7ra5EUja+O5y/IsXXX4ZxR+ZhvfGdXSGA1iSsADUCFI=; h=From:To:Cc:Subject:Date; b=d+AytK0OzfY39sh5oGoKFE2gWnd8q2yfviI8Q3UNnvKepLrkqPEE8BfT6NYTbjv78 gZh4jFHuGM1dKP75jjISGW7HklFFAulg85HiximmTBxI1VzHS1hPHMq+CbwhIfOpw1 kGDv4IZK0iDSdvxw5/p4hqOSspDbzQHgmjz87aMxz8OHgLVHYbeKt6dRvzOdPt8/T/ PqyZQP0lKnYyGyR5J6ltsHYphoqgSD/rah9zptf07NmtaxBqNlGTSzekhsgrnNF8NB 2A2bOF9E996UzOWcJG2Vy/gqHDeCLGH9jjY2OnpUwqnjTkRfACbRW5gnHwkGy3aCz1 UI7BrZV46BUxg== From: Eric Biggers To: stable@vger.kernel.org Cc: linux-ext4@vger.kernel.org, Yao Kai , syzbot+5322c5c260eb44d209ed@syzkaller.appspotmail.com, Zhihao Cheng , Jan Kara , Zhang Yi , Theodore Ts'o , Eric Biggers Subject: [PATCH 6.6] ext4: validate readdir offset before accessing dirent Date: Tue, 27 Oct 2026 17:42:09 -0700 Message-ID: <20261028004209.58412-1-ebiggers@kernel.org> X-Mailer: git-send-email 2.56.0 X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Yao Kai commit bc4b7b0414c33b2c8898eb04386df0d21a13dad8 upstream. 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: Eric Biggers --- 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 6682b8ab11f1c..bc53ea82161d3 100644 --- a/fs/ext4/dir.c +++ b/fs/ext4/dir.c @@ -136,6 +136,7 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx) struct super_block *sb = inode->i_sb; struct buffer_head *bh = NULL; struct fscrypt_str fstr = FSTR_INIT(NULL, 0); + bool has_csum = ext4_has_metadata_csum(sb); err = fscrypt_prepare_readdir(inode); if (err) @@ -147,7 +148,7 @@ 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_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. @@ -233,7 +234,10 @@ 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, file->f_version)) { - 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 @@ -255,6 +259,17 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx) file->f_version = 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); @@ -310,6 +325,7 @@ 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); base-commit: 0aebf2870d53a8d97e02a99e2103ea0b38950c1b -- 2.56.0