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[195.14.216.63]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-492202edec6sm285706305e9.3.2026.06.15.07.46.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Jun 2026 07:46:22 -0700 (PDT) From: Vasileios Almpanis To: Jens Axboe Cc: io-uring@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] io_uring/nop: fix file reference leak with IOSQE_FIXED_FILE Date: Mon, 15 Jun 2026 16:45:57 +0200 Message-ID: <20260615144619.482749-1-vasilisalmpanis@gmail.com> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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. Cc: stable@vger.kernel.org Fixes: a85f31052bce ("io_uring/nop: add support for testing registered files and buffers") Reported-by: syzbot+2cd473471e77bda12b0e@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?id=879092631b98f73a28ea405adacfa5bb34a14a25 Signed-off-by: Vasileios Almpanis --- io_uring/nop.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/io_uring/nop.c b/io_uring/nop.c index 91ae0b2e7e55..60ab19604b36 100644 --- a/io_uring/nop.c +++ b/io_uring/nop.c @@ -40,6 +40,8 @@ int io_nop_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) nop->fd = READ_ONCE(sqe->fd); else nop->fd = -1; + if (nop->flags & IORING_NOP_FIXED_FILE) + req->flags |= REQ_F_FIXED_FILE; if (nop->flags & IORING_NOP_FIXED_BUFFER) req->buf_index = READ_ONCE(sqe->buf_index); if (nop->flags & IORING_NOP_CQE32) { @@ -59,12 +61,10 @@ int io_nop(struct io_kiocb *req, unsigned int issue_flags) int ret = nop->result; if (nop->flags & IORING_NOP_FILE) { - if (nop->flags & IORING_NOP_FIXED_FILE) { + if (req->flags & REQ_F_FIXED_FILE) req->file = io_file_get_fixed(req, nop->fd, issue_flags); - req->flags |= REQ_F_FIXED_FILE; - } else { + else req->file = io_file_get_normal(req, nop->fd); - } if (!req->file) { ret = -EBADF; goto done; -- 2.47.3