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 9EC98330333; Mon, 27 Oct 2025 18:58:46 +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=1761591526; cv=none; b=uQqzEdQ57s0JgmZD2vLh2SMOfC3XqZ8R2GeVyxraocppXhpMPQRKGc18PxdkjlYn5sXGq5YfAZshl6wVKLkAPIELLmwFENYRF1/eAKemH1FBwWg/euhP/oEVZO5UC7qATYjAWKHSxHdaJy22MbEYrKGJ40/r9tU3NeMqKB0WsCI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761591526; c=relaxed/simple; bh=8FLYR/LCaeJaLIM59ednxwF56ntO9wNw8AVdUtxrmnw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=FuzmE9+RvBmDm9syXY6kAby4drIgsq0BGjhBAtNF9T16yQplS67iYb3kl2AZIvq7wQdzvsNLp53FDWlZwcSZM0gxp3gRbk0asN4WaxU4uHwwfCUNkYu5F4XfTjL+4f6G7HGeE+J7i+ep52VnYrgCqMzwW4AzIYjfOYVGxKo726w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Ni2OxErk; 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="Ni2OxErk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4C1B8C4CEF1; Mon, 27 Oct 2025 18:58:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1761591525; bh=8FLYR/LCaeJaLIM59ednxwF56ntO9wNw8AVdUtxrmnw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Ni2OxErkk6DMh5S/9M2H1a854kAQKAjz3FaHCzwv4oRw0Aiii5wiiNcsqep9BnOi+ s480nGUjddFdtWkdsjbm9DmWNaBO1Z1PYjsKSJx8fKiUomN0MTKgf8tJWFLTG2MnMB 5E3tjMEcnAs4w0waFXk2SY43biFDg9oI8FBWECkg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, David Howells , Aleksa Sarai , Christian Brauner , Sasha Levin Subject: [PATCH 5.10 192/332] fscontext: do not consume log entries when returning -EMSGSIZE Date: Mon, 27 Oct 2025 19:34:05 +0100 Message-ID: <20251027183529.756849906@linuxfoundation.org> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20251027183524.611456697@linuxfoundation.org> References: <20251027183524.611456697@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 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Aleksa Sarai [ Upstream commit 72d271a7baa7062cb27e774ac37c5459c6d20e22 ] 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: Sasha Levin 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)