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[209.85.208.170]) by smtp.gmail.com with ESMTPSA id b21sm1893072ljj.46.2020.04.10.15.24.54 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 Apr 2020 15:24:54 -0700 (PDT) Received: by mail-lj1-f170.google.com with SMTP id z26so3299274ljz.11 for ; Fri, 10 Apr 2020 15:24:54 -0700 (PDT) X-Received: by 2002:a2e:b619:: with SMTP id r25mr4239814ljn.150.1586557493736; Fri, 10 Apr 2020 15:24:53 -0700 (PDT) MIME-Version: 1.0 References: <20200410143047.bf34a933ce1affdc042c7c80@linux-foundation.org> <20200410213235.M6eTaELL2%akpm@linux-foundation.org> In-Reply-To: <20200410213235.M6eTaELL2%akpm@linux-foundation.org> From: Linus Torvalds Date: Fri, 10 Apr 2020 15:24:37 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [patch 07/35] mm/gup: fix null pointer dereference detected by coverity To: Andrew Morton , Peter Xu Cc: ira.weiny@intel.com, Linux-MM , miles.chen@mediatek.com, mm-commits@vger.kernel.org Content-Type: text/plain; charset="UTF-8" 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 Fri, Apr 10, 2020 at 2:32 PM Andrew Morton wrote: > > In fixup_user_fault(), it is possible that unlocked is NULL, > so we should test unlocked before using it. This seems wrong. > For example, in arch/arc/kernel/process.c, NULL is passed > to fixup_user_fault(). > > ret = fixup_user_fault(current, current->mm, (unsigned long) uaddr, > FAULT_FLAG_WRITE, NULL); Yes, but it doesn't set FAULT_FLAG_ALLOW_RETRY, exactly _because_ 'unlocked' is NULL. Basically, retry is fundamentally tied to that "unlocked" flag. You can't ask for retry without also saying "please tell me if you unlocked the mmap_sem during the retry". So the two go hand in hand there. So I think this is just coverity not understanding the rules. Or maybe I'm the one missing something. Did you actually see a problem? Linus