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Mon, 15 Jun 2026 09:09:13 -0700 (PDT) Message-ID: <8c1ca105-e27e-4b84-a7c8-f928c05ac7f2@kernel.dk> Date: Mon, 15 Jun 2026 10:09:12 -0600 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] io_uring/nop: fix file reference leak with IOSQE_FIXED_FILE To: Vasileios Almpanis Cc: io-uring@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260615144619.482749-1-vasilisalmpanis@gmail.com> Content-Language: en-US From: Jens Axboe In-Reply-To: <20260615144619.482749-1-vasilisalmpanis@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/15/26 8:45 AM, Vasileios Almpanis wrote: > NOP file-acquisition support choses between a fixed (registered) file and > a normal fget()'d file based on its own IORING_NOP_FIXED_FILE flag in > sqe->nop_flags. However, a request's REQ_F_FIXED_FILE is set > independently from the generic IOSQE_FIXED_FILE sqe flag during request > init, before the issue handler runs. > > If a NOP is submitted with IOSQE_FIXED_FILE set (so REQ_F_FIXED_FILE is > set) but without IORING_NOP_FIXED_FILE, io_nop() takes the normal path > and grabs a real reference via io_file_get_normal(). On completion, > io_put_file() only drops the reference when REQ_F_FIXED_FILE is clear, > so the fget()'d file is never released and leaks: > > BUG: memory leak > unreferenced object 0xffff88800f42c240 (size 176): > kmem_cache_alloc_noprof+0x358/0x440 > alloc_empty_file+0x57/0x180 > path_openat+0x44/0x1e50 > do_file_open+0x121/0x200 > do_sys_openat2+0xa7/0x150 > __x64_sys_openat+0x82/0xf0 > > Decide between fixed and normal file acquisition from REQ_F_FIXED_FILE, > the same way io_assign_file() does for every other opcode, and fold > IORING_NOP_FIXED_FILE into REQ_F_FIXED_FILE at prep time. Fix looks good to me! I've written a test case for this as well, it's in liburing. -- Jens Axboe