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[2003:cb:c708:fe00:8ba4:5871:abc3:8a75]) by smtp.gmail.com with ESMTPSA id t21-20020a1c7715000000b003a331c6bffdsm15938745wmi.47.2022.07.26.00.45.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 26 Jul 2022 00:45:20 -0700 (PDT) Message-ID: <621fb975-413d-a6b4-8126-0b78d5b60853@redhat.com> Date: Tue, 26 Jul 2022 09:45:20 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 To: Qi Zheng , akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Linus Torvalds References: <20220726062436.90290-1-zhengqi.arch@bytedance.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH] mm: fix NULL pointer dereference in wp_page_reuse() In-Reply-To: <20220726062436.90290-1-zhengqi.arch@bytedance.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1658821526; a=rsa-sha256; cv=none; b=ix59JlDB8ck8YYElF3PznT1zUFesyJfG3EwyUDaA7tQfqvjF9lJyGslYsCb7f+68p7bof8 BrMQ+lJhY5Z8semH3bADqen47etiG1pQu1Lm/fErW61B18oGqUkCJNrJfdnyxdKNSBbCY4 K+uCQfisf03SaSd+SRsA+HnwcxTL9zY= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=IbnFJtKL; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf10.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1658821526; 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-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=vKrp0ZOd4wBRpP1jWQmTVuLD91idOPyFfvryoNQLhZ8=; b=4gmg48BUDWxmWiQ0orjqJhBZFTo6ejM8WKYs93DFBc4V9cmDtjHVhngyH3cZlIujeofc8j CmvuDCra5GTblrSuhnqni+dnytnK78LtWA6yOH5BJ9tOHvDi8av2OcWEldf3zVcSc4a//c OMuJ47Epqg5aHPrBvpV1Ccb1Kwj7YPg= X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: A9188C00AA Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=IbnFJtKL; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf10.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com X-Stat-Signature: cx1cowfpumsi4bo1kqgz7q7pn49uw9gg X-HE-Tag: 1658821526-837142 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: On 26.07.22 08:24, Qi Zheng wrote: > 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 Indeed, fortunately, only an issue in the VM_BUG_ON statement Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb