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Sun, 03 May 2026 01:51:24 -0700 (PDT) Received: from m2max ([77.241.229.232]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-67b85e292c2sm2368936a12.1.2026.05.03.01.51.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 03 May 2026 01:51:22 -0700 (PDT) From: Jens Axboe To: io-uring@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, brauner@kernel.org, Jens Axboe , Linus Torvalds Subject: [PATCH 5/5] io_uring/epoll: disallow adding an epoll file to an epoll context Date: Sun, 3 May 2026 02:49:16 -0600 Message-ID: <20260503085101.112698-6-axboe@kernel.dk> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260503085101.112698-1-axboe@kernel.dk> References: <20260503085101.112698-1-axboe@kernel.dk> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit One of the nastier things about epoll is how it allows adding epoll files to epoll contexts. This leads to all sorts of loop detection code, and has been a source of issues in the past. Arguably adding IORING_EPOLL_CTL is a historical mistake on the io_uring side, but we're kind of stuck with it now as it does seem to be in use according to code searches. But we can at least minimize the damage a bit and just disallow this part of epoll, where nesting issues can arise. Suggested-by: Linus Torvalds Signed-off-by: Jens Axboe --- io_uring/epoll.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/io_uring/epoll.c b/io_uring/epoll.c index 59cd4f009648..42057aab9124 100644 --- a/io_uring/epoll.c +++ b/io_uring/epoll.c @@ -62,6 +62,9 @@ int io_epoll_ctl(struct io_kiocb *req, unsigned int issue_flags) CLASS(fd, tf)(ie->fd); if (fd_empty(tf)) return -EBADF; + /* disallow adding an epoll context to another epoll context */ + if (ie->op == EPOLL_CTL_ADD && is_file_epoll(fd_file(tf))) + return -EINVAL; efd.file = fd_file(tf); efd.fd = ie->fd; -- 2.53.0