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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43fe4dc24cfsm52984876f8f.16.2026.04.23.07.04.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Apr 2026 07:04:25 -0700 (PDT) Date: Thu, 23 Apr 2026 15:04:23 +0100 From: David Laight To: "David Hildenbrand (Arm)" Cc: Usama Arif , Alban Crequy , Andrew Morton , Christian Brauner , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Alban Crequy , Peter Xu , Willy Tarreau , linux-kselftest@vger.kernel.org, shuah@kernel.org Subject: Re: [PATCH v2 1/2] mm/process_vm_access: pidfd and nowait support for process_vm_readv/writev Message-ID: <20260423150423.1a428820@pumpkin> In-Reply-To: <62d88cde-efc0-48cb-be8d-813eda810343@kernel.org> References: <20260409142256.131676-1-usama.arif@linux.dev> <62d88cde-efc0-48cb-be8d-813eda810343@kernel.org> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: 14jnyzok3fpamn5dg1aky7wkthx3w18n X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 88AEB80008 X-Rspam-User: X-HE-Tag: 1776953068-106190 X-HE-Meta: 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 CyTAbIG+ 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 23 Apr 2026 14:52:26 +0200 "David Hildenbrand (Arm)" wrote: > >> > >> /* Get process information */ > >> - task = find_get_task_by_vpid(pid); > >> + if (flags & PROCESS_VM_PIDFD) > >> + task = pidfd_get_task(pid, &f_flags); > >> + else > >> + task = find_get_task_by_vpid(pid); > >> + > >> if (!task) { > >> rc = -ESRCH; > >> goto free_proc_pages; > > > > pidfd_get_task() returns ERR_PTR() on failure (e.g. ERR_PTR(-EBADF)), > > but the code checks "if (!task)" which only catches NULL. An invalid > > pidfd will cause mm_access() and put_task_struct() to dereference an > > error pointer, crashing the kernel. > > Yes. Should we add proper selftests that exercise these code paths? > Probably worth checking what happens when a 64bit process tries to read high addresses of a 32bit process. I remember trying to grok the way this code accessed the iov[] and failing to find the appropriate access_ok() for the accesses to the target process. David