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 0B85E30E83A; Tue, 31 Mar 2026 17:08:18 +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=1774976898; cv=none; b=lSug9K2fQ3YPyOfWouwF0RZzB6fM+zwGgcSXt9GAnvGYHn8od63EG49ra3U6P/7fOv4D0qjepBsTbeWzzw80Aci9y8LTSOpQnrfz5s64XgUBW/C3eD7ouml3cB1D8jgBK85mYqAG3wdO8UJIjzZywYA0zMb27rI6g0eR1LRMHSY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774976898; c=relaxed/simple; bh=xJI0hAv+7VgIdtZXIAraDu+lF2wwc3aqrvPqB7vBUyY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Zi8dkuBvfZiIoVr4g58tsX7mjuprpetRE0LaKpHO4P1DZGcXeyyqMqYCa7HXkGglM/BVt2DP6WNB5XOlu/axVqZes+zWarokGMbq445hNHMtT69SV45/6YCT8Y7MY3mO4WH7jf+IODLMPHRbqJxMd/kTmE038fcZayspHvB/d1M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=zU8+mJPE; 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="zU8+mJPE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 940CAC19423; Tue, 31 Mar 2026 17:08:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1774976897; bh=xJI0hAv+7VgIdtZXIAraDu+lF2wwc3aqrvPqB7vBUyY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=zU8+mJPEyBsfJFzaV/czdUBjGKJ8U6pefzPEqPqphWN1auJNmF55E2F7YAPGiMHum YUfcx/XdE3gtnkhchd3D+l23djosSid9JOwmDY+Hzn+wZ/T7lAgpjtP6jijH31OZUK k3+LfQ97W3qC9N600Qm2arMJz3s44dvREEbcGeX8= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jan Kara , Baokun Li , Theodore Tso , stable@kernel.org Subject: [PATCH 6.18 269/309] ext4: handle wraparound when searching for blocks for indirect mapped blocks Date: Tue, 31 Mar 2026 18:22:52 +0200 Message-ID: <20260331161803.463357867@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260331161753.468533260@linuxfoundation.org> References: <20260331161753.468533260@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org 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: Theodore Ts'o commit bb81702370fad22c06ca12b6e1648754dbc37e0f upstream. Commit 4865c768b563 ("ext4: always allocate blocks only from groups inode can use") restricts what blocks will be allocated for indirect block based files to block numbers that fit within 32-bit block numbers. However, when using a review bot running on the latest Gemini LLM to check this commit when backporting into an LTS based kernel, it raised this concern: If ac->ac_g_ex.fe_group is >= ngroups (for instance, if the goal group was populated via stream allocation from s_mb_last_groups), then start will be >= ngroups. Does this allow allocating blocks beyond the 32-bit limit for indirect block mapped files? The commit message mentions that ext4_mb_scan_groups_linear() takes care to not select unsupported groups. However, its loop uses group = *start, and the very first iteration will call ext4_mb_scan_group() with this unsupported group because next_linear_group() is only called at the end of the iteration. After reviewing the code paths involved and considering the LLM review, I determined that this can happen when there is a file system where some files/directories are extent-mapped and others are indirect-block mapped. To address this, add a safety clamp in ext4_mb_scan_groups(). Fixes: 4865c768b563 ("ext4: always allocate blocks only from groups inode can use") Cc: Jan Kara Reviewed-by: Baokun Li Reviewed-by: Jan Kara Signed-off-by: Theodore Ts'o Link: https://patch.msgid.link/20260326045834.1175822-1-tytso@mit.edu Signed-off-by: Theodore Ts'o Cc: stable@kernel.org Signed-off-by: Greg Kroah-Hartman --- fs/ext4/mballoc.c | 2 ++ 1 file changed, 2 insertions(+) --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -1199,6 +1199,8 @@ static int ext4_mb_scan_groups(struct ex /* searching for the right group start from the goal value specified */ start = ac->ac_g_ex.fe_group; + if (start >= ngroups) + start = 0; ac->ac_prefetch_grp = start; ac->ac_prefetch_nr = 0;