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To: Xie Maoyi , Pavel Begunkov , "io-uring@vger.kernel.org" Cc: "linux-kernel@vger.kernel.org" References: Content-Language: en-US From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/8/26 2:34 AM, Xie Maoyi wrote: > Hi Jens, Pavel, > > While testing io_uring with the SQPOLL setup flag from inside an > unprivileged user_ns + pid_ns, I noticed that > /proc//fdinfo/ prints the SQPOLL kthread's host > (init_pid_ns) PID rather than the kthread's PID as seen from the > caller's pid_ns. I'm not sure whether this is intended behaviour > or a bug worth fixing, and would appreciate your view before > sending a patch. > > Reproduction (KASAN, mainline 7.0): a process unshares CLONE_NEWUSER > | CLONE_NEWPID | CLONE_NEWNS, mounts a private /proc, and a > grandchild (PID 1 in the new pid_ns) opens an io_uring ring with > IORING_SETUP_SQPOLL. Inside the new pid_ns: > > /proc/self/task contains {1, 2} # SQPOLL kthread is PID 2 > /proc/self/fdinfo/: > SqThread: 356 # init_pid_ns view (host PID) > > After applying a candidate fix that translates sq->task_pid > through task_pid_nr_ns() against the inode's pid_ns (mirroring > pidfd_show_fdinfo() in kernel/pid.c), the same PoC prints: > > SqThread: 2 # caller's pid_ns view > > Is this expected behaviour, or worth fixing? If a fix would be > welcome, I have a 2+/1- patch in io_uring/fdinfo.c that's > checkpatch-clean and verified pre/post on a KASAN VM. Happy to > send the patch and the full PoC if that's useful. Please send the patch, I do think we should change that. -- Jens Axboe