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 6E4409463; Wed, 5 Aug 2026 02:18:00 +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=1785896281; cv=none; b=QeA2RP8ErpZrGT2biu9o0y25lo+KUMnNFfwxeDvfFQ3VozqvPJt/5Hc/8OupslGnxIyCxADxrRSuDXpuuZUWMOSrcADJfa3N2pNCPS1hIPEC6xxyXPgUH44LM/ZIMcWfVWL3z3TdvAny+EO1urK7p5ycxXhW8ZTwLHSqdqVmodg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785896281; c=relaxed/simple; bh=WfvirnkFtMYeJz0d2XuItJZwCGwWNq8Cn7T/WpFy+kE=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=j7H66ns55ZnA2X5iuKhs8tkWrUlSAKq+ARMWGZ6q6WBNtqxgQUjt4hjrSdzlX2okQSV2y8riMMM58fhKsBhfFllF8QVDZqfv345AE1jqbP0THHgv1FjKoQi4mbqzoJPdkHwpefDoD1QblIQqMDJLTijETghOMvqWYTHRyZGAU3A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZIB0qSz0; 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="ZIB0qSz0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4108A1F000E9; Wed, 5 Aug 2026 02:17:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785896280; bh=EoNhQWZZubP9kzIP7TZ8V1LYEcxSeF9ASil51tIfOYU=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=ZIB0qSz0flDKyNnJBohuQ9hVmy6J+7h0d7eeE+Ff1XJhVbkpkmt304pATxfEDf/EL oDDonwK3YGS5NY7HuoEFl05MKY1BXn0XyYPaX/gWNCG1CnK8NSR8bM8B/fMz2wNugx lnGW4T+wC+d7OvgfwSQ5XVLFLYxuXVw8rr019wZZ54AAqd6+RuDlBRJfrJNOcd93wB lT681TjIZ51o8FWi/eedBtmiOinr8tyzy2bGuHYaptjwO2XmEn5TrH0Srmzaw4BiQf IJTBx0X5X1er5ez+B9afBS8ofo+diuc35z78EQixH2XU86aQBkDAAmu3kPAJ1tM5rA k0asS/5B62BVA== Date: Tue, 4 Aug 2026 19:17:58 -0700 From: Jakub Kicinski To: Jijie Shao Cc: , , , , , , , , , , , , , , Subject: Re: [PATCH v4 net] net: page_pool: fix UAF in __page_pool_release_netmem_dma on xa_cmpxchg race Message-ID: <20260804191758.0f2009f7@kernel.org> In-Reply-To: <20260731111507.2355601-1-shaojijie@huawei.com> References: <20260731111507.2355601-1-shaojijie@huawei.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Fri, 31 Jul 2026 19:15:07 +0800 Jijie Shao wrote: > page_pool_scrub() iterates pool->dma_mapped via xa_for_each() with no > page ref held. __page_pool_release_netmem_dma() currently reads and > writes netmem fields (dma_addr, DMA index bits in pp_magic) after > xa_cmpxchg() returns. The unref path calls put_page() unconditionally > regardless of the cmpxchg outcome; when it loses the cmpxchg, it still > frees the page before the scrub winner finishes these netmem accesses, > so scrub touches a freed page -- a Use-After-Free. > > Fix this by splitting the DMA release into two functions: > > 1. __page_pool_unmap_netmem_dma() caches dma_addr before xa_cmpxchg(), > does the cmpxchg to remove the DMA mapping, and calls dma_unmap on > the cached address. It never touches netmem fields after the cmpxchg, > making it safe for the scrub path which holds no page ref. > > 2. __page_pool_release_netmem_dma() wraps the above and additionally > clears dma_addr and DMA index bits in netmem fields. This is safe > only when the caller holds a page ref, so it is used by the return > path (page_pool_return_netmem). > > The scrub path calls __page_pool_unmap_netmem_dma() directly; the return > path calls __page_pool_release_netmem_dma(). Please clearly state what led you to discovering this bug? Was it directly hit in production? Was there a prod issue which made you investigate? Were you able to trigger the race and if so -- how? > Fixes: ee62ce7a1d90 ("page_pool: Track DMA-mapped pages and unmap them when destroying the pool") > Suggested-by: Mina Almasry > Assisted-by: OhMyOpenCode:GLM-5.2 > Signed-off-by: Jijie Shao > --- > Changes in v4: > - Restructure per Mina's review: merge page_pool_remove_dma_mapping() > into __page_pool_unmap_netmem_dma() with dma_unmap inlined via goto > label; simplify __page_pool_release_netmem_dma() to a thin wrapper. > - Link to v3: https://lore.kernel.org/r/20260729110249.2824835-1-shaojijie@huawei.com > > Changes in v3: > - Fix unlikely() to likely() for PP_DMA_INDEX_BITS to match > file convention. > - Link to v2: https://lore.kernel.org/r/20260727132612.3277927-1-shaojijie@huawei.com > > Changes in v2: > - Redesign the fix per Mina's review: v1's unconditional > netmem_set_dma_index() introduced a UAF when the scrub path > (no page ref) writes to a page freed by the unref path. > - Cache dma_addr before xa_cmpxchg; move dma_addr/DMA index > cleanup to page_pool_return_netmem() which holds a page ref. > - Rename page_pool_release_dma_index() to > page_pool_remove_dma_mapping() to reflect its new role as a > pure cmpxchg wrapper. > - Link to v1: https://lore.kernel.org/r/20260724092135.414699-1-shaojijie@huawei.com > --- > net/core/page_pool.c | 46 ++++++++++++++++++++++---------------------- > 1 file changed, 23 insertions(+), 23 deletions(-) > > diff --git a/net/core/page_pool.c b/net/core/page_pool.c > index 21dc4a9c8714..497bb1906fc3 100644 > --- a/net/core/page_pool.c > +++ b/net/core/page_pool.c > @@ -500,29 +500,40 @@ static int page_pool_register_dma_index(struct page_pool *pool, > return err; > } > > -static int page_pool_release_dma_index(struct page_pool *pool, > - netmem_ref netmem) > +static void __page_pool_unmap_netmem_dma(struct page_pool *pool, > + netmem_ref netmem) > { > struct page *old, *page = netmem_to_page(netmem); > unsigned long id; > + dma_addr_t dma; > + > + if (!pool->dma_map) > + return; > + > + /* Cache dma_addr before xa_cmpxchg. The scrub path holds no page ref; > + * the unref path calls put_page() regardless of cmpxchg outcome, so > + * after the cmpxchg we cannot safely touch netmem fields. > + */ > + dma = page_pool_get_dma_addr_netmem(netmem); > > if (unlikely(!PP_DMA_INDEX_BITS)) > - return 0; > + goto unmap; nit: just indent the intervening lines please. Don't use goto where adding a code block would do. > id = netmem_get_dma_index(netmem); > if (!id) > - return -1; > + return; > > if (in_softirq()) > old = xa_cmpxchg(&pool->dma_mapped, id, page, NULL, 0); > else > old = xa_cmpxchg_bh(&pool->dma_mapped, id, page, NULL, 0); > if (old != page) > - return -1; > - > - netmem_set_dma_index(netmem, 0); > + return; > > - return 0; > +unmap: > + dma_unmap_page_attrs(pool->p.dev, dma, > + PAGE_SIZE << pool->p.order, pool->p.dma_dir, > + DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_WEAK_ORDERING); > } -- pw-bot: cr