From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 97CFCC76196 for ; Thu, 6 Apr 2023 11:53:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237308AbjDFLxX (ORCPT ); Thu, 6 Apr 2023 07:53:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41964 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237174AbjDFLwv (ORCPT ); Thu, 6 Apr 2023 07:52:51 -0400 Received: from mail-pf1-x42a.google.com (mail-pf1-x42a.google.com [IPv6:2607:f8b0:4864:20::42a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AF0E5CA05 for ; Thu, 6 Apr 2023 04:49:25 -0700 (PDT) Received: by mail-pf1-x42a.google.com with SMTP id q20so14446026pfs.2 for ; Thu, 06 Apr 2023 04:49:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1680781729; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=UqUdWcIc9KSCHCHXJ8GC3elQeDVWFp/Z+QbNbi6Nyag=; b=aR/R13ai1AiVhyWTBhytZjSZDeRATzoRuYARLGrrUvl6hsRK9KD8w6g+C9dCsDKq3v IAMVb5i+l3/38biq7+Ev68o+Sb+8EcQz7R2hdhkUNnOVHFb8cbDN4v0GWcKaNW2lzVsB MODbm33ZPeVwyt5ptnVHYEAYX+mCdPx0IdrI2qAmbFMNbJLAut3Ymz3Sf5vSxU0SrtQV rEGZITMSifUtDY1VmVndKnp5CTPleUC/TV2n1MSaYgfkKOhVanG3YG/MrSfIUznh28r0 DylfonkRyB/nY2+bw7FK9SlwqWuYY4XN1rteJMShXc6Jj4qFBWqBy4PQA168J1Ji/T/I ateQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680781729; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=UqUdWcIc9KSCHCHXJ8GC3elQeDVWFp/Z+QbNbi6Nyag=; b=eYalceCHqkr8mXI3rVo6r/laH6gw4WAqtxw3LmIivb11KJhu/FlDluotTo1c7SGJr8 yq5xCNPYTZ9gTxE9rWLkk5BEjrdrFyz2GJX2c1z7aFujnhcJGRyo8dajwl6QBg2gGvIP HUy1zefc125VBuyI3Yt3eLbxHHhwdJ4w2jdfisZVYr3DETb97bb2LtA615IDt4C1mRei Ouwv9MYsBgFknN3VvZERgjazl8Y3J+Za5sKwHEQTdAAfSSbsGabgOj21hnKkjan6K5we RosC5Tyn5GkPxSCnmYSrLXFOMvxPHDbKkXWgLMbV7SjqWXEnLmFn13CvO5uwyy1zZWKW zOUg== X-Gm-Message-State: AAQBX9ff2OXOWCPGOtpWeOrnfjcFczQP6DlNDVs/wEP97PkcgAm02mWC kM9LzlciI3PmUUdB0qlh9dM= X-Google-Smtp-Source: AKy350ZedNhOaa4J+OnYSq9MhGcSFGMoguZhS7Y1cmBfEgfB+DQSLp5asqYMU/PTciZOCEsrcRAoyw== X-Received: by 2002:a62:84d6:0:b0:62e:11:6bd with SMTP id k205-20020a6284d6000000b0062e001106bdmr9568511pfd.25.1680781728797; Thu, 06 Apr 2023 04:48:48 -0700 (PDT) Received: from localhost.localdomain ([155.94.207.39]) by smtp.gmail.com with ESMTPSA id bm1-20020a056a00320100b0062dd993fdfcsm1214712pfb.105.2023.04.06.04.48.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Apr 2023 04:48:47 -0700 (PDT) From: Liang Chen To: kuba@kernel.org, alexander.duyck@gmail.com, ilias.apalodimas@linaro.org, hawk@kernel.org Cc: davem@davemloft.net, edumazet@google.com, pabeni@redhat.com, netdev@vger.kernel.org, liangchen.linux@gmail.com Subject: [PATCH v2] skbuff: Fix a race between coalescing and releasing SKBs Date: Thu, 6 Apr 2023 19:48:25 +0800 Message-Id: <20230406114825.18597-1-liangchen.linux@gmail.com> X-Mailer: git-send-email 2.31.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Commit 1effe8ca4e34 ("skbuff: fix coalescing for page_pool fragment recycling") allowed coalescing to proceed with non page pool page and page pool page when @from is cloned, i.e. to->pp_recycle --> false from->pp_recycle --> true skb_cloned(from) --> true However, it actually requires skb_cloned(@from) to hold true until coalescing finishes in this situation. If the other cloned SKB is released while the merging is in process, from_shinfo->nr_frags will be set to 0 towards the end of the function, causing the increment of frag page _refcount to be unexpectedly skipped resulting in inconsistent reference counts. Later when SKB(@to) is released, it frees the page directly even though the page pool page is still in use, leading to use-after-free or double-free errors. So it needs to be specially handled at where the ref count may get lost. The double-free error message below prompted us to investigate: BUG: Bad page state in process swapper/1 pfn:0e0d1 page:00000000c6548b28 refcount:-1 mapcount:0 mapping:0000000000000000 index:0x2 pfn:0xe0d1 flags: 0xfffffc0000000(node=0|zone=1|lastcpupid=0x1fffff) raw: 000fffffc0000000 0000000000000000 ffffffff00000101 0000000000000000 raw: 0000000000000002 0000000000000000 ffffffffffffffff 0000000000000000 page dumped because: nonzero _refcount CPU: 1 PID: 0 Comm: swapper/1 Tainted: G E 6.2.0+ Call Trace: dump_stack_lvl+0x32/0x50 bad_page+0x69/0xf0 free_pcp_prepare+0x260/0x2f0 free_unref_page+0x20/0x1c0 skb_release_data+0x10b/0x1a0 napi_consume_skb+0x56/0x150 net_rx_action+0xf0/0x350 ? __napi_schedule+0x79/0x90 __do_softirq+0xc8/0x2b1 __irq_exit_rcu+0xb9/0xf0 common_interrupt+0x82/0xa0 asm_common_interrupt+0x22/0x40 RIP: 0010:default_idle+0xb/0x20 Signed-off-by: Liang Chen --- Changes from v1: - deal with the ref count problem instead of return back to give more opportunities to coalesce skbs. --- net/core/skbuff.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 050a875d09c5..77da8ce74a1e 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -5643,7 +5643,19 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from, skb_fill_page_desc(to, to_shinfo->nr_frags, page, offset, skb_headlen(from)); - *fragstolen = true; + + /* When @from is pp_recycle and @to isn't, coalescing is + * allowed to proceed if @from is cloned. However if the + * execution reaches this point, @from is already transitioned + * into non-cloned because the other cloned skb is released + * somewhere else concurrently. In this case, we need to make + * sure the ref count is incremented, not directly stealing + * from page pool. + */ + if (to->pp_recycle != from->pp_recycle) + get_page(page); + else + *fragstolen = true; } else { if (to_shinfo->nr_frags + from_shinfo->nr_frags > MAX_SKB_FRAGS) @@ -5659,7 +5671,13 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from, from_shinfo->nr_frags * sizeof(skb_frag_t)); to_shinfo->nr_frags += from_shinfo->nr_frags; - if (!skb_cloned(from)) + /* Same situation as above where head data presents. When @from is + * pp_recycle and @to isn't, coalescing is allowed to proceed if @from + * is cloned. However @from can be transitioned into non-cloned + * concurrently by this point. If it does happen, we need to make sure + * the ref count is properly incremented. + */ + if (to->pp_recycle == from->pp_recycle && !skb_cloned(from)) from_shinfo->nr_frags = 0; /* if the skb is not cloned this does nothing -- 2.18.2