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Mon, 25 Jul 2022 23:25:32 -0700 (PDT) From: Qi Zheng To: akpm@linux-foundation.org, david@redhat.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qi Zheng Subject: [PATCH] mm: fix NULL pointer dereference in wp_page_reuse() Date: Tue, 26 Jul 2022 14:24:36 +0800 Message-Id: <20220726062436.90290-1-zhengqi.arch@bytedance.com> X-Mailer: git-send-email 2.24.3 (Apple Git-128) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1658816736; a=rsa-sha256; cv=none; b=hMddgdULlEyEMjHdIAD30kwnOxh9VN7KHLzhIYyvW3lU6EpHhtaQuVefnROD9kC8N9hyup w322cAjyZ4rC/aLa2yFtsB2kBBNaOQnuTKh8Iz84vESnWJIJnUwJd50FVg03EkzQl1zTyc tR3lOttbBdKPdTHhQxOxHyXmY7nzzZw= ARC-Authentication-Results: i=1; imf31.hostedemail.com; dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=ie3eJ3v2; dmarc=pass (policy=none) header.from=bytedance.com; spf=pass (imf31.hostedemail.com: domain of zhengqi.arch@bytedance.com designates 209.85.210.174 as permitted sender) smtp.mailfrom=zhengqi.arch@bytedance.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1658816736; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:references:dkim-signature; bh=AdOoxODJiumCfXGJPDqlgTRMx1Hwty97pt6JnuBcVOQ=; b=Gf2/A2qpXkIB1Oa2BtkxSph2K8uAwxDcQkOqm6ezFYoyIuBRj8VGgucrWaWvCEkyUD4G2U 5VXIbw9uZ41PxZsW8sSs99vkis01EiQyC/gLQUh0dVba3gNwdU+spSRG+ngdGrjEA69h0p r92KqZBFBSei8k/xA5yUsNmF/RVT2JU= Authentication-Results: imf31.hostedemail.com; dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=ie3eJ3v2; dmarc=pass (policy=none) header.from=bytedance.com; spf=pass (imf31.hostedemail.com: domain of zhengqi.arch@bytedance.com designates 209.85.210.174 as permitted sender) smtp.mailfrom=zhengqi.arch@bytedance.com X-Stat-Signature: bxdfkr791nkmgitg93bieek6mrbx1t9h X-Rspamd-Queue-Id: 3622F200A1 X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1658816734-940241 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: The vmf->page can be NULL when the wp_page_reuse() is invoked by wp_pfn_shared(), it will cause the following panic: [ 12.981200] BUG: kernel NULL pointer dereference, address: 000000000000008 [ 12.981954] #PF: supervisor read access in kernel mode [ 12.982615] #PF: error_code(0x0000) - not-present page [ 12.983146] PGD 0 P4D 0 [ 12.983417] Oops: 0000 [#1] PREEMPT SMP PTI [ 12.983846] CPU: 18 PID: 923 Comm: Xorg Not tainted 5.19.0-rc8.bm.1-amd64 #263 [ 12.984606] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g14 [ 12.985760] RIP: 0010:_compound_head+0x0/0x40 [...] [ 12.995932] Call Trace: [ 12.996199] [ 12.996424] wp_page_reuse+0x1c/0xa0 [ 12.996800] do_wp_page+0x1a5/0x3f0 [ 12.997169] __handle_mm_fault+0x8cf/0xd20 [ 12.997587] ? _raw_spin_unlock_irqrestore+0x23/0x35 [ 12.998105] handle_mm_fault+0xd5/0x2a0 [ 12.998499] do_user_addr_fault+0x1d0/0x680 [ 12.998930] exc_page_fault+0x78/0x170 [ 12.999321] asm_exc_page_fault+0x22/0x30 To fix it, this patch performs a NULL pointer check before dereferencing the vmf->page. Fixes: 6c287605fd56 ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive") Signed-off-by: Qi Zheng --- mm/memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index 4cf7d4b6c950..9174918ce3f7 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3043,7 +3043,7 @@ static inline void wp_page_reuse(struct vm_fault *vmf) pte_t entry; VM_BUG_ON(!(vmf->flags & FAULT_FLAG_WRITE)); - VM_BUG_ON(PageAnon(page) && !PageAnonExclusive(page)); + VM_BUG_ON(page && PageAnon(page) && !PageAnonExclusive(page)); /* * Clear the pages cpupid information as the existing -- 2.20.1