From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 DEF6E31B82C; Mon, 27 Oct 2025 18:44:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761590670; cv=none; b=ZIl6kiaQEKu8z2woUkbNtVoE4OLrr+h3fneKRYWChawExUm6f6+NYkBX+V21bkEuVNRJgpDncxeWvPQum1RJD0oNWouhI0u1dHMbSpwaYJRCQZS4IZd+meLroRShbAFGVQAe4CPGVYesaN1jbhN58utj5D+b2TmE4L0rERGyeAQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761590670; c=relaxed/simple; bh=ZQ1Pga82YqKwa2yMoQoAKF+D1THFdS+l3H8QjKDn9Nw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=owoK2D0Vp3l14ie9YMPn/AJ6ta05EjUCdabjsQJa04Poce5/Rzcdipryhqhg5paNK+r7HkOM++hdWdioSoPJFX7xrwQqEtee+Zku0vgqn7eD/NVPp3FgS+eL9qnJQVGIE9lJe48ncnT7m/Ca+GLZcw9k0a5POCFEH9erI4IQk6Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=2SwqDeV0; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="2SwqDeV0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 22195C4CEF1; Mon, 27 Oct 2025 18:44:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1761590669; bh=ZQ1Pga82YqKwa2yMoQoAKF+D1THFdS+l3H8QjKDn9Nw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=2SwqDeV0LPdn3QMGuHDVgz6VcD+0E8sBG3AZdOdAeI/AbRiitZvO7f19XRyLa0nM9 h7jBhoF8qrPttA3Q+r5xy4y64wn01Cm6Z7zdb67FRns/euDhM6cFUby9yEoY2MhPaB mvB4f5XV7pVYRdeHlcJfpL5OMpIOgjtr4nwZ7N7c= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+0be4f339a8218d2a5bb1@syzkaller.appspotmail.com, stable@kernel.org, Albin Babu Varghese , Ahmet Eray Karadag , Theodore Tso Subject: [PATCH 5.4 131/224] ext4: guard against EA inode refcount underflow in xattr update Date: Mon, 27 Oct 2025 19:34:37 +0100 Message-ID: <20251027183512.486516430@linuxfoundation.org> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20251027183508.963233542@linuxfoundation.org> References: <20251027183508.963233542@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 5.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ahmet Eray Karadag commit 57295e835408d8d425bef58da5253465db3d6888 upstream. syzkaller found a path where ext4_xattr_inode_update_ref() reads an EA inode refcount that is already <= 0 and then applies ref_change (often -1). That lets the refcount underflow and we proceed with a bogus value, triggering errors like: EXT4-fs error: EA inode ref underflow: ref_count=-1 ref_change=-1 EXT4-fs warning: ea_inode dec ref err=-117 Make the invariant explicit: if the current refcount is non-positive, treat this as on-disk corruption, emit ext4_error_inode(), and fail the operation with -EFSCORRUPTED instead of updating the refcount. Delete the WARN_ONCE() as negative refcounts are now impossible; keep error reporting in ext4_error_inode(). This prevents the underflow and the follow-on orphan/cleanup churn. Reported-by: syzbot+0be4f339a8218d2a5bb1@syzkaller.appspotmail.com Fixes: https://syzbot.org/bug?extid=0be4f339a8218d2a5bb1 Cc: stable@kernel.org Co-developed-by: Albin Babu Varghese Signed-off-by: Albin Babu Varghese Signed-off-by: Ahmet Eray Karadag Message-ID: <20250920021342.45575-1-eraykrdg1@gmail.com> Signed-off-by: Theodore Ts'o Signed-off-by: Greg Kroah-Hartman --- fs/ext4/xattr.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) --- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -1030,7 +1030,7 @@ static int ext4_xattr_inode_update_ref(h int ref_change) { struct ext4_iloc iloc; - s64 ref_count; + u64 ref_count; int ret; inode_lock_nested(ea_inode, I_MUTEX_XATTR); @@ -1040,13 +1040,17 @@ static int ext4_xattr_inode_update_ref(h goto out; ref_count = ext4_xattr_inode_get_ref(ea_inode); + if ((ref_count == 0 && ref_change < 0) || (ref_count == U64_MAX && ref_change > 0)) { + ext4_error_inode(ea_inode, __func__, __LINE__, 0, + "EA inode %lu ref wraparound: ref_count=%lld ref_change=%d", + ea_inode->i_ino, ref_count, ref_change); + ret = -EFSCORRUPTED; + goto out; + } ref_count += ref_change; ext4_xattr_inode_set_ref(ea_inode, ref_count); if (ref_change > 0) { - WARN_ONCE(ref_count <= 0, "EA inode %lu ref_count=%lld", - ea_inode->i_ino, ref_count); - if (ref_count == 1) { WARN_ONCE(ea_inode->i_nlink, "EA inode %lu i_nlink=%u", ea_inode->i_ino, ea_inode->i_nlink); @@ -1055,9 +1059,6 @@ static int ext4_xattr_inode_update_ref(h ext4_orphan_del(handle, ea_inode); } } else { - WARN_ONCE(ref_count < 0, "EA inode %lu ref_count=%lld", - ea_inode->i_ino, ref_count); - if (ref_count == 0) { WARN_ONCE(ea_inode->i_nlink != 1, "EA inode %lu i_nlink=%u",