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Tue, 07 Apr 2020 18:40:15 -0700 (PDT) Received: from xz-x1.hitronhub.home ([2607:9880:19c0:32::3]) by smtp.gmail.com with ESMTPSA id a186sm18438740qkg.2.2020.04.07.18.40.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Apr 2020 18:40:15 -0700 (PDT) From: Peter Xu To: linux-kernel@vger.kernel.org, Linus Torvalds , linux-mm@kvack.org Cc: Andrew Morton , peterx@redhat.com, syzbot+693dc11fcb53120b5559@syzkaller.appspotmail.com Subject: [PATCH 1/2] mm/mempolicy: Allow lookup_node() to handle fatal signal Date: Tue, 7 Apr 2020 21:40:09 -0400 Message-Id: <20200408014010.80428-2-peterx@redhat.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200408014010.80428-1-peterx@redhat.com> References: <20200408014010.80428-1-peterx@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com 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: lookup_node() uses gup to pin the page and get node information. It checks against ret>=0 assuming the page will be filled in. However it's also possible that gup will return zero, for example, when the thread is quickly killed with a fatal signal. Teach lookup_node() to gracefully return an error -EFAULT if it happens. Meanwhile, initialize "page" to NULL to avoid potential risk of exploiting the pointer. Reported-by: syzbot+693dc11fcb53120b5559@syzkaller.appspotmail.com Fixes: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple times") Signed-off-by: Peter Xu Signed-off-by: Michal Hocko --- mm/mempolicy.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 5fb427aed612..c7ca6a808fb1 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -897,12 +897,15 @@ static void get_policy_nodemask(struct mempolicy *p, nodemask_t *nodes) static int lookup_node(struct mm_struct *mm, unsigned long addr) { - struct page *p; + struct page *p = NULL; int err; int locked = 1; err = get_user_pages_locked(addr & PAGE_MASK, 1, 0, &p, &locked); - if (err >= 0) { + if (err == 0) { + /* E.g. GUP interrupted by fatal signal */ + err = -EFAULT; + } else if (err > 0) { err = page_to_nid(p); put_page(p); }