From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=209.85.216.54 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793550793; b=1HIVG0PSPRtx+JnMjXa7sqLy6kfy/UhKpJ7gLaDvxAlnn7LmVfN66BQGRPlgsa9lrHQy G+4m/j1/HTbvLk9GqIkvxmdH1qLrWoIxpJnVj7xfkmt3iN4R/XaDAAMO3wB65r8Dsphwg NRyvuq07MJNegYJBiPLracPwK7tNH8JT38PsussVy4JwHXvO1hUY7r50P06WB+KqoN2QQ IYB9XOTOvWU5zwI/cdkp3hH3rSz7V9cx7lsXo/iWijrAYNw/lJsHyU4fSTZGkanC6YBGu TyUCUYiQ4jVajgPQNv4I6UxeKA2evAgWAUPGneUPCNxl1POTYwYKkvajdxqsJOSj/5A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793550793; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Gm-Gg:X-Received:Received: From:To:Cc:Subject:Date:Message-ID:X-Mailer:MIME-Version: Content-Transfer-Encoding; bh=z1wgGnLaHoKZu2/+Ud078CAK3gozxrFVUFtZdHR2t7Q=; b=N4l59sIUKR7V1sCGA2xpkKJhW0g7kzmH3WVNW0d09F2GNHKEgy5mpZcrjmG9CbGSGRGT U3uBPYaIobxv5bfMzqmXJ5YYjGBBOtVxPU9aRJsUT0rtnv14fUh+880keDk//jRnQCmM8 kgzX7hcGYvyGzc9sBIgE/NVo0NAPj9+/QIw+fOMluXDmqyBL6iPKwS+PRBBBJXk1rVccO eJkpjHC1TPlev0ZL1YyrYmXj2Ug1AR56gq2Sk0+1mhWLKEGgchG2bhaIWPAIn+V6kU5qe RZEfZLavWd14xiZmPjQdLSeCHOGSRCaI+YcQ7bwgEaMfYIbQMtfxXsrV3MaZwbLMKNg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=i+MmRGdI; arc=none smtp.remote-ip=209.85.216.54 Received: from mail-pj1-f54.google.com (mail-pj1-f54.google.com [209.85.216.54]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2E4EA606A324 for ; Sun, 1 Nov 2026 16:33:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 2E4EA606A324 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=i+MmRGdI Received: by mail-pj1-f54.google.com with SMTP id 98e67ed59e1d1-3acb1224533so366796a91.2 for ; Sun, 01 Nov 2026 08:33:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20260707; t=1793550792; x=1794155592; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to:content-type; bh=z1wgGnLaHoKZu2/+Ud078CAK3gozxrFVUFtZdHR2t7Q=; b=i+MmRGdIPHvaRXB6Fj5arp1lNW1XvIIeAqBKs39M6I8fVaRMTNTti9f8p04KTbn2XG gbDrcBvUa4PwHLtFllbkEw7Lv3nKjpseY45dmaOaWamcTIPECpieM203pt0MX3DPu6wL 0Ko55HWdibTQBzFsD5RjIN0rN13+B0e1jnKQgPTWpX9ruwkSZ9SuomHRJeFnowbRAfWE eDl/9ndwfg2OVwP2o3kPLE7ThVvlsVMAUtT6Uyrk70DkfjRxq/8lnslsaOXH+5GzyIeM QqogZYk1vFXPM6tzNa0oBql/6pITmvdDOy5OEq9VQPlgR2eyb9pL3u/4CS7YYAXr9Rvj sssw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1793550792; x=1794155592; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=z1wgGnLaHoKZu2/+Ud078CAK3gozxrFVUFtZdHR2t7Q=; b=cU4mIIUv+FV4Kr0tZtIu5IXI/gb0s7JOeXVz+fiXlINklCJx7a6eZxzni0gxEk9ERB zF8bceFPlp64mTzZqRIyxaqXZWYonIJdmKKEyP62Gbji5T86xSvm7hqR0D+v3p3MCVoV mGW9f/qaUh95t3j+XzGgB4OhAtdq+De1nKjItwB9kY4VlyMwfqA4C6Jv5hfNz7Fl8NWC ahIRk8G14cVSVQot05FAAD5EmpwKElhxt33CeRi0N280rATIKf5uZV0n1zUa+0Kol2En x5WyQErjmsjahWk8UuHHMpmK3Tkb9VZ80cBdhav39WZH8CeMziMZAKZSHv8hhYGQHq4z mJtw== X-Forwarded-Encrypted: i=1; AKwUvBwaLW2bUWOqZVdlPzExL63SBPEjD6eQyTVtRIRkAO5dQjikW8YeZUkxVnykL/nK2tPxdeu5/18NGyyL9jk=@vger.kernel.org X-Gm-Message-State: APuU4Z/A4vDfv+w3m1f/mdnVbdcGEA49O2l7PLAh+mPC58cSM+5lLozw I7+BWYd8Jvhg46eY79z5oEeVNHa7TnL7q6Pm6XxWoEiB7tITXkQI82yO X-Gm-Gg: AYBFou2Dbol1w9SZwtJCYUWl7qrKlARk/u0fQTS1C485Hei76WRly6jR7X3Hlh2oEWh WocEeRg1U8Bxf4GaeUKH2s+4KpFLFqmwzN8V44AY8nLrqvmbzkEQ2Y89L2qUWxCfK+hy+/mUZ7i +6xLA8BObiIjRYd6dDB6l0VEOt7m4r/yGpGiJSg+MIEGQmtJMJv60ryO3wBHnCFdq/WVmcR8EWF rAtZXKF1vH6R/83VAH/BAZciCGO78MhJdgnFPUvnMFGNeaB8RzJRAc0wIXejt7baSPG7QLzPsaY WGuQstF8PDqIrlKZvUES1axVQQDJXvrDCjLTXiFQKGIFajZQUwY7B97U5UD52gPMQgvhm1CjO3g LwykWemsvPgZwPbEFG8UtA9j7PxbXteVOq5E/UufdBzS3LE8w7OQEGW3D/utkq1Dbfox9Y/qgcv Tx8HXZ6oouNYcLn8Zawq4E77f//0x/Ojl8exfE1a8JWzfawMIAidIi01kqtnJY3POeArMhrlvgC viFPKY5fek7OShIyziIHpoqbVTBgY0CG9x7g908RtTrZUp32G2YNxi9XXEsbM/34vSIgA6ZdWp4 Y4jrmo61wN6qDdkWOhiIeD66XLJ+TCP29fqxACqH9mr+VPzvc/o9rB5DwziUUvedS0gOU6U+3jp 9rlE5Co6TFVMx0qFSO6ojZfI= X-Received: by 2002:a17:90b:1808:b0:3ab:a188:b898 with SMTP id 98e67ed59e1d1-3ae895f8623mr10840887a91.2.1793550792550; Sun, 01 Nov 2026 08:33:12 -0800 (PST) Received: from localhost.localdomain ([113.102.236.131]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-cdb0981c5desm2063394a12.27.2026.11.01.08.33.06 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sun, 01 Nov 2026 08:33:11 -0800 (PST) From: Qihang To: Juergen Gross , xen-devel@lists.xenproject.org Cc: Stefano Stabellini , Oleksandr Tyshchenko , Viresh Kumar , linux-kernel@vger.kernel.org, Qihang , stable@vger.kernel.org Subject: [PATCH] xen/privcmd: fix double free when an irqfd is shut down twice Date: Mon, 2 Nov 2026 00:32:50 +0800 Message-ID: <20261101163251.55099-1-q.h.hack.winter@gmail.com> X-Mailer: git-send-email 2.54.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit irqfd_deactivate() takes the irqfd off irqfds_list and queues irqfd_shutdown(). queue_work() is not a once-only gate: it refuses to enqueue a work item only while WORK_STRUCT_PENDING is set, and process_one_work() clears that bit before it calls the work function. So nothing records that the shutdown work has already been queued, and nothing protects the window between the start of irqfd_shutdown() and the kfree() at its end. Two paths call irqfd_deactivate() for the same irqfd: - privcmd_irqfd_deassign(), from the PRIVCMD_IRQFD_FLAG_DEASSIGN ioctl; - irqfd_wakeup(), with EPOLLHUP set, when the last reference to the eventfd file goes away, which runs wake_up_poll(&ctx->wqh, EPOLLHUP) from eventfd_release(). irqfds_lock serialises the two calls, but it does not make the second one a no-op, and eventfd_ctx_fdget() takes a reference to the eventfd_ctx, not to the struct file, so the last fd can still be closed while the ioctl is running: CPU0 CPU1 eventfd_ctx_fdget() spin_lock(irqfds_lock) list_del_init(&kirqfd->list) queue_work(&kirqfd->shutdown) close(fd) eventfd_release() wake_up_poll(EPOLLHUP) irqfd_wakeup() spin_lock(irqfds_lock) irqfd_deactivate() again If the work item has already started by then, its pending bit has been cleared and the second queue_work() succeeds. irqfd_shutdown() then runs twice, so eventfd_ctx_remove_wait_queue(), eventfd_ctx_put() and kfree() each hit the same object a second time; and when the second queue_work() lands after the irqfd has been freed, the workqueue list operations write to freed memory. virt/kvm/eventfd.c has the same two callers and has had this guard since the original irqfd support (721eecbf4fe99): irqfd_wakeup() calls irqfd_deactivate() only if irqfd_is_active(). The comment there explains why that is enough: the other side deactivates the irqfd before it takes it off the waitqueue, and irqfd_shutdown() needs the waitqueue lock, which this callback holds, so the irqfd cannot be freed under it. Do the same here. list_del_init() leaves the list head empty and the irqfd stays off the list until kfree(), so it serves as a one-way "active" flag. The test is in irqfd_deactivate() rather than in irqfd_wakeup() because privcmd_irqfd_deassign() walks irqfds_list and can therefore never reach an inactive irqfd; only the wakeup path can, and a single test covers both callers. Fixes: f8941e6c4c712 ("xen: privcmd: Add support for irqfd") Cc: stable@vger.kernel.org Signed-off-by: Qihang --- drivers/xen/privcmd.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c index 5e56fbc934478..221b31611343e 100644 --- a/drivers/xen/privcmd.c +++ b/drivers/xen/privcmd.c @@ -901,10 +901,25 @@ struct privcmd_kernel_irqfd { poll_table pt; }; +static bool irqfd_is_active(struct privcmd_kernel_irqfd *kirqfd) +{ + lockdep_assert_held(&irqfds_lock); + + return !list_empty(&kirqfd->list); +} + static void irqfd_deactivate(struct privcmd_kernel_irqfd *kirqfd) { lockdep_assert_held(&irqfds_lock); + /* + * Both the deassign ioctl and the eventfd wakeup path can reach + * this function. list_del_init() marks the irqfd inactive, so + * only the first caller may queue the shutdown work. + */ + if (!irqfd_is_active(kirqfd)) + return; + list_del_init(&kirqfd->list); queue_work(irqfd_cleanup_wq, &kirqfd->shutdown); } -- 2.54.0 (Apple Git-157)