From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 7FE77246783; Fri, 17 Oct 2025 14:56:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760713008; cv=none; b=LX+cEBtnKK1053wYKVattJI5JargeoSOjv2jffO0DBaOMM3pP7oLfbLLCP3A0BbR37ZSFkXEkbWgWcKzivaSK4ZMJih8Yx/bKlvjDmEuNnzeJi9EZAf4LJTjtskKiyx/AZnH9XdeV6QWcWqMrQTZEUdIDNYmXvfNvYtKxyqdofc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760713008; c=relaxed/simple; bh=W9F/E2KgZG2O/8k5ZFAQeRKa4ZPuAR0ZuVew+Rn2pPE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jH4IFh2SKNbpqvQI2+zUHeVDXipI6DTAfDRh6ZxQt37tcnc6PNsf9A2c2ay9YrgH3/ZHcE1IX3HjbrYGHNOKYe5HYsT/HDME8+hY+5IaIYMlW9WePj05oqBhtnQIDtqGKjta7eJ8Z1xDe1ZDUrtJiQ9p6erZlM3XIks91SRpjL8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Wj/9ElJA; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Wj/9ElJA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B8D68C4CEE7; Fri, 17 Oct 2025 14:56:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1760713008; bh=W9F/E2KgZG2O/8k5ZFAQeRKa4ZPuAR0ZuVew+Rn2pPE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Wj/9ElJA5WZR0CeINCwcXJREAk2/8NsP1DZu7tbIoH5e228EWnGHG76y1oTVAOEXG 3QbLUzVm0TskATw4m73f/34G0gKKn6lfJ6If4AQd0xPJCvwG775yQgegN/+vlUSrdn cCI4V6r+/RGVIHxeSjoPc1qYHYSG4obP5X4NcOx0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, David Howells , Aleksa Sarai , Christian Brauner Subject: [PATCH 6.1 002/168] fscontext: do not consume log entries when returning -EMSGSIZE Date: Fri, 17 Oct 2025 16:51:21 +0200 Message-ID: <20251017145129.094806860@linuxfoundation.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251017145129.000176255@linuxfoundation.org> References: <20251017145129.000176255@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-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Aleksa Sarai commit 72d271a7baa7062cb27e774ac37c5459c6d20e22 upstream. Userspace generally expects APIs that return -EMSGSIZE to allow for them to adjust their buffer size and retry the operation. However, the fscontext log would previously clear the message even in the -EMSGSIZE case. Given that it is very cheap for us to check whether the buffer is too small before we remove the message from the ring buffer, let's just do that instead. While we're at it, refactor some fscontext_read() into a separate helper to make the ring buffer logic a bit easier to read. Fixes: 007ec26cdc9f ("vfs: Implement logging through fs_context") Cc: David Howells Cc: stable@vger.kernel.org # v5.2+ Signed-off-by: Aleksa Sarai Link: https://lore.kernel.org/20250807-fscontext-log-cleanups-v3-1-8d91d6242dc3@cyphar.com Signed-off-by: Christian Brauner Signed-off-by: Greg Kroah-Hartman --- fs/fsopen.c | 70 ++++++++++++++++++++++++++++++++---------------------------- 1 file changed, 38 insertions(+), 32 deletions(-) --- a/fs/fsopen.c +++ b/fs/fsopen.c @@ -18,50 +18,56 @@ #include "internal.h" #include "mount.h" +static inline const char *fetch_message_locked(struct fc_log *log, size_t len, + bool *need_free) +{ + const char *p; + int index; + + if (unlikely(log->head == log->tail)) + return ERR_PTR(-ENODATA); + + index = log->tail & (ARRAY_SIZE(log->buffer) - 1); + p = log->buffer[index]; + if (unlikely(strlen(p) > len)) + return ERR_PTR(-EMSGSIZE); + + log->buffer[index] = NULL; + *need_free = log->need_free & (1 << index); + log->need_free &= ~(1 << index); + log->tail++; + + return p; +} + /* * Allow the user to read back any error, warning or informational messages. + * Only one message is returned for each read(2) call. */ static ssize_t fscontext_read(struct file *file, char __user *_buf, size_t len, loff_t *pos) { struct fs_context *fc = file->private_data; - struct fc_log *log = fc->log.log; - unsigned int logsize = ARRAY_SIZE(log->buffer); - ssize_t ret; - char *p; + ssize_t err; + const char *p __free(kfree) = NULL, *message; bool need_free; - int index, n; - - ret = mutex_lock_interruptible(&fc->uapi_mutex); - if (ret < 0) - return ret; - - if (log->head == log->tail) { - mutex_unlock(&fc->uapi_mutex); - return -ENODATA; - } + int n; - index = log->tail & (logsize - 1); - p = log->buffer[index]; - need_free = log->need_free & (1 << index); - log->buffer[index] = NULL; - log->need_free &= ~(1 << index); - log->tail++; + err = mutex_lock_interruptible(&fc->uapi_mutex); + if (err < 0) + return err; + message = fetch_message_locked(fc->log.log, len, &need_free); mutex_unlock(&fc->uapi_mutex); + if (IS_ERR(message)) + return PTR_ERR(message); - ret = -EMSGSIZE; - n = strlen(p); - if (n > len) - goto err_free; - ret = -EFAULT; - if (copy_to_user(_buf, p, n) != 0) - goto err_free; - ret = n; - -err_free: if (need_free) - kfree(p); - return ret; + p = message; + + n = strlen(message); + if (copy_to_user(_buf, message, n)) + return -EFAULT; + return n; } static int fscontext_release(struct inode *inode, struct file *file)