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 DB8B54F5DF0; Thu, 17 Sep 2026 16:59:25 +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=1789664367; cv=none; b=muM6DcUzjmF80LrEiCtZF6DTvBbxd64u1Vn72Dy8WkPxzsLvUE3JAgILfbKaa32RPEQeVg5DcF0K1bQek38qFb4IsFRHi0r1Qzze3s0jq2aM2isyTVw3aR6E2zzygC3ktcwt/QHsF+dh5Uh4inMl2PzkvKeG5dmeAb8v5zGeJVE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789664367; c=relaxed/simple; bh=xaijL55iDNeVEu8qUjgX1q55OESgTNVgeuvyUKSJ3oQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=d0oa3k+zMV6fKcihGAV67goxq6PXrguiKCTlYTd1PU9pfb9OKvwvING65zE+VmNUUmT+YB0iH6SaX9eurp02m1EcOGIc1e6DKsX/SRLg7138qbgaaEvVbhdoRXZnMqXLrFfBpoZvCydyILinkSh19kpiIZylWoJIwimWiAcxfFU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=0uUZoMGx; 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="0uUZoMGx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 393491F000FF; Thu, 17 Sep 2026 16:59:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789664365; bh=4nvygmSoEm+9AXyzpWqOG/2jT+hGPf6BuoDfTXDhZsQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=0uUZoMGxbX719B7qFvpEcJOItZdIK0pn0ZGVULnzZ39Tn30j7eE1hI50DrYb/nVSZ bBnp+KajUCWgPmcrdD8HjxqDowM3PJrJc5eXLuGucrMMORUT0iCM7o1Ulqz/CnrhHN abvajY3+UnGWHBmnooA1Ds7ZW9/o9zAPHhlzZWeE= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, ZhengYuan Huang , David Sterba , Sasha Levin Subject: [PATCH 6.18 0349/1250] btrfs: balance: fix potential bg lookup failure in btrfs_may_alloc_data_chunk() Date: Thu, 17 Sep 2026 16:02:24 +0100 Message-ID: <20260917151601.530553608@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260917151551.901433442@linuxfoundation.org> References: <20260917151551.901433442@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: ZhengYuan Huang [ Upstream commit 18d32b0013efba19f7ad3e5b08d7aee813d604a6 ] [BUG] Running btrfs balance can trigger a null-ptr-deref before relocating a data chunk when metadata corruption leaves a chunk in the chunk tree without a corresponding block group in the in-memory cache: KASAN: null-ptr-deref in range [0x0000000000000088-0x000000000000008f] RIP: 0010:btrfs_may_alloc_data_chunk+0x40/0x1c0 fs/btrfs/volumes.c:3601 Call Trace: __btrfs_balance fs/btrfs/volumes.c:4217 [inline] btrfs_balance+0x2516/0x42b0 fs/btrfs/volumes.c:4604 btrfs_ioctl_balance fs/btrfs/ioctl.c:3577 [inline] btrfs_ioctl+0x25cf/0x5b90 fs/btrfs/ioctl.c:5313 ... [CAUSE] __btrfs_balance() iterates the on-disk chunk tree and passes the chunk logical bytenr to btrfs_may_alloc_data_chunk() before relocating a data chunk. That helper then queries the in-memory block group cache: cache = btrfs_lookup_block_group(fs_info, chunk_offset); chunk_type = cache->flags; /* cache may be NULL */ A corrupt image can contain a chunk item whose matching block group item is missing, so no block group is ever inserted into the cache. In that case btrfs_lookup_block_group() returns NULL. The code only guards this with ASSERT(cache), which becomes a no-op when CONFIG_BTRFS_ASSERT is disabled. The subsequent dereference of cache->flags therefore crashes the kernel. [FIX] Add a NULL check after btrfs_lookup_block_group() in btrfs_may_alloc_data_chunk() and print and error message for clarity. Signed-off-by: ZhengYuan Huang Reviewed-by: David Sterba Signed-off-by: David Sterba Signed-off-by: Sasha Levin --- fs/btrfs/volumes.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 51c3eab54bde6..fe81ff417c0d8 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -3719,7 +3719,11 @@ static int btrfs_may_alloc_data_chunk(struct btrfs_fs_info *fs_info, u64 chunk_type; cache = btrfs_lookup_block_group(fs_info, chunk_offset); - ASSERT(cache); + if (unlikely(!cache)) { + btrfs_err(fs_info, "balance: chunk at bytenr %llu has no corresponding block group", + chunk_offset); + return -EUCLEAN; + } chunk_type = cache->flags; btrfs_put_block_group(cache); -- 2.53.0