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 9B3BE3A0E86; Fri, 11 Sep 2026 06:16:26 +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=1789107387; cv=none; b=lUpIExs9xU2Hc3d5NTvnrvD4JIgpG7Ex1qw3jfJJs75O28bBFoWsDlMmbP8Qvoe2S4mOMLzXco0aZn6dnu9X789N20Ziff4cZQPTINelVwiemJ6KjVAYCOh7VfcWwXZ7uGBPEVvf85e8FmXqpdx7ZSM7WHhPWbFEyK3n0v/H9ss= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789107387; c=relaxed/simple; bh=CfOksVLUV1Ea73r0dqtEQHcC87P3L6wWw8avOJAAQGM=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=nT9x2RqFo03wrT9iqf0fkG9/cBNDr4eDM3KDjdwuQk4sEy4cvOq+G60ogrprOiliW4uy2UWCYhsSJipAI7ymUIZ7PKL/2rnEzLfGfCEJkEh23vVZOx7kqrWItNzLe/sIJomDX8ABH/Ex1Bh2l+fs96RFn5xPhnWo5ctj2uBC6VI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BAQH+gGY; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="BAQH+gGY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 821401F000FF; Fri, 11 Sep 2026 06:16:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789107386; bh=FeqXMA8IIsuw3Bo3s6IikFZ8TcQWGZ07dRERboDu9wU=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=BAQH+gGYpy4oo9sUsyrqQnrsDNIXCE17tcvebrHtzQfPKUezQkFC8/X/WAIzoGgVn jVo8N3RLvSl7dJrOY8Z2S5J015d2uIn2jMR2vG0XJjsEQkPe+PHelPoy6njvEZT3H1 9urmATZNGrv4PsjbT8yO+Gg6TtF1gocz9r4Mp40HiD4we7kPoOv4MbBzddNO3PS1AL 4R8hno71pkyYNoRubTowW0WQe+xF5hruGtZF+UtqXTWdyybOZnf813Bv16K2M5zoIH oZAHsE9ZMkcOtTkeDN00c5X7FEtlx2WTasMVMjelohJoMeZTeMg5UCZZTzbvXxpd9k xZgf9FOngow+Q== Date: Fri, 11 Sep 2026 15:16:21 +0900 From: Masami Hiramatsu (Google) To: Sang-Heon Jeon Cc: Andrew Morton , Breno Leitao , Christian Brauner , Thomas Gleixner , Ryan Roberts , Thomas =?UTF-8?B?V2Vpw59zY2h1aA==?= , Douglas Anderson , Huacai Chen , Mark Rutland , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH v4 2/2] bootconfig: Fix integer overflow in initrd size check Message-Id: <20260911151621.a111896e0cd75bb3ebbe232b@kernel.org> In-Reply-To: References: <178905331374.213925.295025394754459843.stgit@devnote2> <178905333479.213925.1358412668943562406.stgit@devnote2> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Fri, 11 Sep 2026 01:29:48 +0900 Sang-Heon Jeon wrote: > On Fri, Sep 11, 2026 at 12:15 AM Masami Hiramatsu (Google) > wrote: > > > > From: Masami Hiramatsu (Google) > > > > Sashiko reported that in get_boot_config_from_initrd(), a crafted initrd > > with a huge bootconfig size (such as 0xFFFFFFFF) can cause the pointer > > arithmetic: > > > > data = ((void *)hdr) - size; > > > > to wrap around on 32-bit systems (or when pointer subtraction overflows). > > Because data wraps around, the subsequent bounds check: > > > > if ((unsigned long)data < initrd_start) > > > > evaluates to false, bypassing the check. The kernel then calls > > xbc_calc_checksum(data, size), which attempts to read 4GB of memory, > > hitting unmapped pages and triggering a fatal kernel page fault during > > early boot. Furthermore, on 64-bit systems with an initrd > 4.29 GB, an > > unbounded 32-bit size can similarly bypass the initrd_start check. > > > > Fix this by: > > 1. Ensuring the initrd is at least large enough to contain the bootconfig > > footer and verifying hdr is within the initrd bounds. > > 2. Checking that size does not exceed XBC_DATA_MAX and does not exceed > > the available space between initrd_start and hdr before performing > > pointer subtraction. > > > > Fixes: de462e5f1071 ("bootconfig: Fix to remove bootconfig data from initrd while boot") > > Cc: stable@vger.kernel.org > > Reported-by: Sashiko > > Closes: https://lore.kernel.org/all/20260910010137.EE0431F000FF@smtp.kernel.org/ > > Assisted-by: Antigravity:gemini-3.8-flash > > Signed-off-by: Masami Hiramatsu (Google) > > --- > > Changes in v4: > > - Accurate the error message for size > XBC_DATA_MAX in > > get_boot_config_from_initrd(). > > - Remove redundant (and wrong) size >= XBC_DATA_MAX check from > > setup_boot_config(). > > --- > > init/main.c | 25 +++++++++++++++---------- > > 1 file changed, 15 insertions(+), 10 deletions(-) > > > > diff --git a/init/main.c b/init/main.c > > index 2613d3f9b3ce..16749bb7a219 100644 > > --- a/init/main.c > > +++ b/init/main.c > > @@ -277,7 +277,8 @@ static void * __init get_boot_config_from_initrd(size_t *_size) > > u8 *hdr; > > int i; > > > > - if (!initrd_end) > > + if (!initrd_end || initrd_end < initrd_start || > > + initrd_end - initrd_start < BOOTCONFIG_MAGIC_LEN + 8) > > return NULL; > > (nit) how about moving BOOTCONFIG_FOOTER_SIZE from tools and using it instead? OK, that will be done in cleanup patch. > > > data = (char *)initrd_end - BOOTCONFIG_MAGIC_LEN; > > @@ -294,16 +295,26 @@ static void * __init get_boot_config_from_initrd(size_t *_size) > > > > found: > > hdr = (u8 *)(data - 8); > > + if ((unsigned long)hdr < initrd_start) > > + return NULL; > > + > > size = get_unaligned_le32(hdr); > > csum = get_unaligned_le32(hdr + 4); > > > > - data = ((void *)hdr) - size; > > - if ((unsigned long)data < initrd_start) { > > - pr_err("bootconfig size %d is greater than initrd size %ld\n", > > + if (size > XBC_DATA_MAX) { > > + pr_err("bootconfig size %u is greater than max size %d\n", > > + size, XBC_DATA_MAX); > > + return NULL; > > + } > > + > > + if (size > ((unsigned long)hdr - initrd_start)) { > > + pr_err("bootconfig size %u is greater than initrd size %lu\n", > > size, initrd_end - initrd_start); > > return NULL; > > } > > > > + data = ((void *)hdr) - size; > > + > > if (xbc_calc_checksum(data, size) != csum) { > > pr_err("bootconfig checksum failed\n"); > > return NULL; > > @@ -394,12 +405,6 @@ static void __init setup_boot_config(void) > > return; > > } > > > > - if (size >= XBC_DATA_MAX) { > > - pr_err("bootconfig size %ld greater than max size %d\n", > > - (long)size, XBC_DATA_MAX); > > - return; > > - } > > - > > Nice cleanup! > > > ret = xbc_init(data, size, &msg, &pos); > > if (ret < 0) { > > if (pos < 0) > > > > Thanks for doing this work! > > Reviewed-by: Sang-Heon Jeon > Thanks! -- Masami Hiramatsu (Google)