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 353271C6FF5; Fri, 17 Apr 2026 04:42:46 +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=1776400967; cv=none; b=jkFYRbFVu15n5VVMkP6n8KNqZD4pkQuHYFnHZqAsxBjfgdrHGktmofyImwtHP8fAslbxtaCaOrIxkfNoZGfDGzdqnSS4xBwtjmNks+DYCf9W3hM1t7OSlCcgEKlbihs20usqDISxWNQbuuFhoBPmmzAc0NURZsDFkV/ff/GU0Io= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776400967; c=relaxed/simple; bh=+kZcyO2YZoRks810z1foc/yqdqsP8AdQc/GigncPdOY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ABTm1lZXY1u3y0h9bkHcFdw6dw7Pwa1DxQtsXMB6r7sLgxal4ay5xYuPAsjS6Z3ePcn/ImMrFOLUSI7RPkO4o3l/iCSuanEILvTAORxi/bruflCxo19EIKmwHWgFN6C47FXJCqRyCcNXfnn6yyM1SXeKof2P6+yJvgwewuL9ucc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pfGQ5i1V; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="pfGQ5i1V" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6DAF1C19425; Fri, 17 Apr 2026 04:42:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776400966; bh=+kZcyO2YZoRks810z1foc/yqdqsP8AdQc/GigncPdOY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=pfGQ5i1VLFUUh34+/+2ZJ/V44nhKo2xNclSoGPtwovtCwj1cG6ZQf3ti3r2EXSitX 7mJyT9d3TCfs9780go8IhtH920vp4qoBQX/crZM7RcTWAUfaaKUOFLC3mIRX3/KG/L ACBjM+96sMBelsfvWCPPQ3/PUGHEc0GFrCIlNHk+Vrm0hczq+b6Hq6tKw1KVXkac/3 Vuk31u6o8Z35yuYIwebWWKYd45HalbXTjzQCVp2BGG4GZchpN7iBVY8ZAkEkVQ7WJn Ghw9ik03Fu3oBmqTiQvABV5dKdd0zntiU0pdUPsA08r7MWtR3DivtjD29SkfohQNsX 3drwy+Ol8BqVA== Date: Fri, 17 Apr 2026 13:42:44 +0900 From: "Harry Yoo (Oracle)" To: Marco Elver Cc: Vlastimil Babka , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, stable@vger.kernel.org, Vitaly Wool , Uladzislau Rezki , Danilo Krummrich , Lorenzo Stoakes , "Liam R. Howlett" , Alice Ryhl , rust-for-linux@vger.kernel.org Subject: Re: [PATCH] slub: fix data loss and overflow in krealloc() Message-ID: References: <20260416132837.3787694-1-elver@google.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260416132837.3787694-1-elver@google.com> [+Cc relevant folks] On Thu, Apr 16, 2026 at 03:25:07PM +0200, Marco Elver wrote: > Commit 2cd8231796b5 ("mm/slub: allow to set node and align in > k[v]realloc") introduced the ability to force a reallocation if the > original object does not satisfy new alignment or NUMA node, even when > the object is being shrunk. > > This introduced two bugs in the reallocation fallback path: > > 1. Data loss during NUMA migration: The jump to 'alloc_new' happens > before 'ks' and 'orig_size' are initialized. As a result, the > memcpy() in the 'alloc_new' block would copy 0 bytes into the new > allocation. Ouch. > 2. Buffer overflow during shrinking: When shrinking an object while > forcing a new alignment, 'new_size' is smaller than the old size. > However, the memcpy() used the old size ('orig_size ?: ks'), leading > to an out-of-bounds write. Right. before the commit we didn't reallocate when the size is smaller. > The same overflow bug exists in the kvrealloc() fallback path, where the > old bucket size ksize(p) is copied into the new buffer without being > bounded by the new size. > > A simple reproducer: > > // e.g. add to lkdtm as KREALLOC_SHRINK_OVERFLOW > while (1) { > void *p = kmalloc(128, GFP_KERNEL); > p = krealloc_node_align(p, 64, 256, GFP_KERNEL, NUMA_NO_NODE); > kfree(p); > } > > demonstrates the issue: > > ================================================================== > BUG: KFENCE: out-of-bounds write in memcpy_orig+0x68/0x130 > > Out-of-bounds write at 0xffff8883ad757038 (120B right of kfence-#47): > memcpy_orig+0x68/0x130 > krealloc_node_align_noprof+0x1c8/0x340 > lkdtm_KREALLOC_SHRINK_OVERFLOW+0x8c/0xc0 [lkdtm] > lkdtm_do_action+0x3a/0x60 [lkdtm] > ... > > kfence-#47: 0xffff8883ad756fc0-0xffff8883ad756fff, size=64, cache=kmalloc-64 > > allocated by task 316 on cpu 7 at 97.680481s (0.021813s ago): > krealloc_node_align_noprof+0x19c/0x340 > lkdtm_KREALLOC_SHRINK_OVERFLOW+0x8c/0xc0 [lkdtm] > lkdtm_do_action+0x3a/0x60 [lkdtm] > ... > ================================================================== > > Fix it by moving the old size calculation to the top of __do_krealloc() > and bounding all copy lengths by the new allocation size. > > Fixes: 2cd8231796b5 ("mm/slub: allow to set node and align in k[v]realloc") > Cc: > Reported-by: https://sashiko.dev/#/patchset/20260415143735.2974230-1-elver%40google.com > Signed-off-by: Marco Elver > --- Looks good to me, but I think we still have a similar issue in vrealloc_node_align_noprof()? (goto need_realloc; due to NUMA mismatch but the new size is smaller) -- Cheers, Harry / Hyeonggon