From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7811C43B4A2; Tue, 21 Jul 2026 21:55:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784670930; cv=none; b=jSjGoe/+ffDvG8JQctIND4gSp9lsSJZs/JixZWvkbmJCXX4vn/lu/7Y/1P06+m6i60aixEilzxfr8i2P6E5zezkEhR83QkCPtbENfVcUolTNedyHEcFERxfkUnbbWbWGI2Iv+eL7zT7tb++ByIoStqM7/qlwtspbe4178+MQhSo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784670930; c=relaxed/simple; bh=OMWpbq8YQ12iwtXfIUWwDI24LDHhQUurCzVw99lLoIY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=lbSWtb2l97wLluEEsTfTlp3FuMRJzvxR3bCRCm19cGgIgcZ6015CSsTk6b5JQYZ3+W2igv//15jpYelK4pPN0NwvVjfzPtScXysDB4SELs2LHbSrcQP93XoB0vwbvQ2+33rBAWFIjMcTHg6njM3sCiuruon60SknFC172hAbN9Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=RviS9J1S; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="RviS9J1S" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DD5AD1F000E9; Tue, 21 Jul 2026 21:55:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784670929; bh=UGYntsEcrKt1nwPW2j3hpCd7LKeLXRl7l5bmcQxFaiA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=RviS9J1S4dOaLLz8KEvxjZ9FoeMT/yIHIEtyv05Y/4AUQj7RUw8LkuQ+9O17kNDfZ XIUO31DnZoDS1JwohqcbR81s5cCx4pEZoz9CUNOzCBmprOqAdcWGodaQeF19Hyddf0 46EQgHxSkCtAe+0kE3fTDBbGqW0+LmJ2/CD0VhzU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Lars-Peter Clausen , =?UTF-8?q?Nuno=20S=C3=A1?= , Stable@vger.kernel.org, Jonathan Cameron Subject: [PATCH 5.15 054/843] iio: event: Fix event FIFO reset race Date: Tue, 21 Jul 2026 17:14:49 +0200 Message-ID: <20260721152407.200515530@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260721152405.946368001@linuxfoundation.org> References: <20260721152405.946368001@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Lars-Peter Clausen commit af791d295737ea6b6ff2c8d8488462a49c14af01 upstream. `iio_event_getfd()` creates the event file descriptor with `anon_inode_getfd()`, which allocates a new fd, creates the anonymous file and installs it in the process fd table before returning to the caller. The IIO code resets the event FIFO after `anon_inode_getfd()` has returned, but before `IIO_GET_EVENT_FD_IOCTL` has copied the fd number to userspace. But since fd tables are shared between threads, another thread can guess the newly allocated fd number and issue a `read()` on it as soon as the fd has been installed. This means the `kfifo_to_user()` in `iio_event_chrdev_read()` can run in parallel with the `kfifo_reset_out()` in `iio_event_getfd()`. The kfifo documentation says that `kfifo_reset_out()` is only safe when it is called from the reader thread and there is only one concurrent reader. Otherwise it is dangerous and must be handled in the same way as `kfifo_reset()`. If that happens, `kfifo_to_user()` can advance the FIFO `out` index based on state from before the reset, after the reset has already moved the `out` index to the current `in` index. That can leave the FIFO with an `out` index past the `in` index. A later `read()` can then see an underflowed FIFO length and copy more data than the event FIFO buffer contains. This can result in an out-of-bounds read and leak adjacent kernel memory to userspace. Move the FIFO reset before `anon_inode_getfd()`. At that point the event fd is marked busy, but the new fd has not been installed yet, so userspace cannot access it while the FIFO is reset. Fixes: b91accafbb10 ("iio:event: Fix and cleanup locking") Reported-by: Codex:gpt-5.5 Signed-off-by: Lars-Peter Clausen Reviewed-by: Nuno Sá Cc: Signed-off-by: Jonathan Cameron Signed-off-by: Greg Kroah-Hartman --- drivers/iio/industrialio-event.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) --- a/drivers/iio/industrialio-event.c +++ b/drivers/iio/industrialio-event.c @@ -207,6 +207,8 @@ static int iio_event_getfd(struct iio_de goto unlock; } + kfifo_reset_out(&ev_int->det_events); + iio_device_get(indio_dev); fd = anon_inode_getfd("iio:event", &iio_event_chrdev_fileops, @@ -214,10 +216,7 @@ static int iio_event_getfd(struct iio_de if (fd < 0) { clear_bit(IIO_BUSY_BIT_POS, &ev_int->flags); iio_device_put(indio_dev); - } else { - kfifo_reset_out(&ev_int->det_events); } - unlock: mutex_unlock(&indio_dev->mlock); return fd;