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[185.147.214.8]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-44a9879ef89sm4089588f8f.30.2026.05.01.01.52.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 01 May 2026 01:52:33 -0700 (PDT) From: Ming Lei To: Jens Axboe , linux-block@vger.kernel.org Cc: Caleb Sander Mateos , Uday Shankar , Ming Lei Subject: [PATCH] ublk: reject FETCH from non-userspace context Date: Fri, 1 May 2026 16:52:16 +0800 Message-ID: <20260501085216.905401-1-tom.leiming@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit __ublk_fetch() sets io->task to current, which is later checked against io_uring_cmd_get_task() in ublk_uring_cmd_cancel_fn(). With REQ_F_FORCE_ASYNC, the FETCH uring_cmd can be issued from task work, which can be run from io_uring's fallback workqueue, causing a task mismatch and triggering the WARN in cancel_fn. Reject FETCH if current is not a real userspace task, and it is reasonable for failing it in case of io_uring fallback. Fixes: 3421c7f68bba ("ublk: make sure io cmd handled in submitter task context") Signed-off-by: Ming Lei --- drivers/block/ublk_drv.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c index 8e5f3738c203..57abc0e9681f 100644 --- a/drivers/block/ublk_drv.c +++ b/drivers/block/ublk_drv.c @@ -3251,12 +3251,19 @@ static int __ublk_fetch(struct io_uring_cmd *cmd, struct ublk_device *ub, WARN_ON_ONCE(io->flags & UBLK_IO_FLAG_OWNED_BY_SRV); - ublk_fill_io_cmd(io, cmd); - - if (ublk_dev_support_batch_io(ub)) + if (ublk_dev_support_batch_io(ub)) { WRITE_ONCE(io->task, NULL); - else + } else { + /* + * FETCH must come from a real userspace task, not a + * kworker is actually io_uring fallback workqueue. + */ + if (current->flags & (PF_KTHREAD | PF_WQ_WORKER)) + return -EINVAL; WRITE_ONCE(io->task, get_task_struct(current)); + } + + ublk_fill_io_cmd(io, cmd); return 0; } -- 2.53.0