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 0B24338737B; Thu, 27 Aug 2026 07:47:15 +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=1787816838; cv=none; b=RZVjKJh92uD1msLGin+utF0yEZK0mncKsNejUlnlbjJC1kSz+ncUuhyKnPZ+yss/NzgfFveeO2FsJl4VCw/kHg98+fYKYGx5JKt9upcW0pbU6bJOAJd/XVD4+sgf8zxJHVk04/bhpG/zZ2D+IiXjmmdIQIzFmZ5UxfLAMEwcN4Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787816838; c=relaxed/simple; bh=D9iRynStFiinHNFk3YUubpgCjzHKcAiB1h/04CNvTa8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=U3zaHU+Ncb6Km0NDV/4uv+OcUVSS/sjnrQq0EAq4Ws44Y6tO4XTRUKh1bidpx9jnyaJ1ZUnKHpWmwQaakk7wSnAeO1CC3VsUH6HrKejLzXHXKNx+MQ3/SUbYUiNmomTmQYy/ZAUynkpXhlWAv0BkmQhf9q4rOWfH/IWLxILO8pM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jXJQAfnV; 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="jXJQAfnV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8C4451F00A3A; Thu, 27 Aug 2026 07:47:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787816834; bh=HAx27bjYWIezR+l7iw/n59Tjpp+JZqYjQalST4GROaY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=jXJQAfnVvTVWEWNE4VPcqMrW72bz1eQ9s0q/9pxGB/zaGdI3wBRdVVIhDL5nvhCmY lC3j0jOHD+sfzJqcAIE01FVPTZ5zMFBDKqvdCxB4RdEUGSVHfsxj9pAUyDem3DiiDc Cs/0u+1y1bxBZ0NGH32qI+TEeFnu2EmwnR4ii55QrS9wtra/TlmA1P96dBkZ2ounLw KWrarGBk+zvC9/3bFuYSbxLGuHNb/v8r0LAC3s1+v8nHQmhrn8SW4gcaOnq9pU2cJ/ y0Lk4h7yDpuPuQXAVg9pKeTOuPqRAwSr8o0SOA8bMx6ZPREh+zz8paYvSEhJSAIbRr KJlwyQO2cFMPQ== Message-ID: Date: Thu, 27 Aug 2026 09:47:08 +0200 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/slab: reject unsupported kmalloc sizes To: Zi Yan , Harry Yoo Cc: Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Alan Stern , Greg Kroah-Hartman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, syzbot+805630f1453e490427fa@syzkaller.appspotmail.com, stable@vger.kernel.org References: <20260817-limit_kmalloc_size-v1-1-5bef487701cc@nvidia.com> <82f138f5-11d4-4839-94a3-c226fd982715@kernel.org> From: "Vlastimil Babka (SUSE)" Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/26/26 11:52 PM, Zi Yan wrote: > On Wed Aug 26, 2026 at 5:47 PM EDT, Harry Yoo wrote: >> On Wed, Aug 26, 2026 at 11:28:12AM +0000, Vlastimil Babka (SUSE) wrote: >>> On 8/17/26 22:40, Zi Yan wrote: >>>> kmalloc is used to allocate physically contiguous memory for kernel >>>> allocations. For requests larger than KMALLOC_MAX_CACHE_SIZE, kmalloc uses >>>> the page allocator and can only support up to KMALLOC_MAX_SIZE. For request >>>> sizes bigger than KMALLOC_MAX_SIZE, the page allocator can emit a WARN >>>> because kmalloc allocates an order greater than MAX_PAGE_ORDER. Systems >>>> with panic_on_warn=1 crash because of this WARN. Fix it by rejecting any >>>> kmalloc size bigger than KMALLOC_MAX_SIZE. >>>> >>>> Fixes: aadb4bc4a1f9 ("SLUB: direct pass through of page size or higher kmalloc requests") >>>> Reported-by: syzbot+805630f1453e490427fa@syzkaller.appspotmail.com >>>> Closes: https://lore.kernel.org/all/6a820ebc.9ebadd4d.20b15e.001b.GAE@google.com/ >>>> Tested-by: syzbot+805630f1453e490427fa@syzkaller.appspotmail.com >>>> Signed-off-by: Zi Yan >>>> Cc: stable@vger.kernel.org >>>> --- >>>> It fixes a page allocator warning (order > MAX_PAGE_ORDER) when gadgetfs >>>> requests excessively large memory from kmalloc. Instead of adding >>>> __GFP_NOWARN to suppress the warning, as was done for usbfs[1], change >>>> kmalloc to return NULL without a warning for this specific issue. >>>> >>>> [1] commit 4f2629ea67e72 ("USB: usbfs: Don't WARN about excessively large memory allocations") >>> >>> So I checked and for kvmalloc() we have in __kvmalloc_node_noprof() >>> >>> /* Don't even allow crazy sizes */ >>> if (unlikely(size > INT_MAX)) { >>> WARN_ON_ONCE(!(flags & __GFP_NOWARN)); >>> return NULL; >>> } >>> >>> This comes from Linus in commit 7661809d493b4. I'd do the same thing here >>> then. >> >> But the purpose of this patch is to avoid the warning in the page >> allocator. Should we fix this in the caller (gadgetfs) then? > > It is fixed by: https://lore.kernel.org/all/20260820223719.A4A3C1F000E9@smtp.kernel.org/ > > Please disregard this patch, but we can keep the discussion going. I still think this patch has some value if done as proposed above. Yes in practice it will just replace the page allocator's warning with a different warning, but IMHO it's "nicer" if kmalloc() sanitizes its own requests to the page allocator, using the KMALLOC_MAX_SIZE value. >> >>> Thus there would be a useful warning for e.g. development mistakes >>> resulting in the size to be unexpectedly high. >>> >>> Callers passing size that comes from userspace or similar untrusted source >>> can either pass __GFP_NOWARN or sanitize the size to what they expect to be >>> sane (which is context dependent and I assume actually way lower than >>> kmalloc limits in practice). Note that passing even sizes within but close >>> to/at the limit, trusting blindly some external source, can succeed the >>> allocations but effectively DoS the system with heavy reclaim/compaction. So >>> caller sanitization should still be preferred IMHO. Some of the recent >>> arguments from Linus [1] would apply to this too, I think. >>> >>> [1] >>> https://lore.kernel.org/all/CAHk-=wiSmgwwLKCqJwGS-dVHnSLU8W+7q1UQq-G9=TBGGZbuhQ@mail.gmail.com/ > > > >