From 007ec26cdc9fefacbed85b592afc69413194499c Mon Sep 17 00:00:00 2001 From: David Howells Date: Thu, 1 Nov 2018 23:34:29 +0000 Subject: vfs: Implement logging through fs_context Implement the ability for filesystems to log error, warning and informational messages through the fs_context. These can be extracted by userspace by reading from an fd created by fsopen(). Error messages are prefixed with "e ", warnings with "w " and informational messages with "i ". Inside the kernel, formatted messages are malloc'd but unformatted messages are not copied if they're either in the core .rodata section or in the .rodata section of the filesystem module pinned by fs_context::fs_type. The messages are only good till the fs_type is released. Note that the logging object is shared between duplicated fs_context structures. This is so that such as NFS which do a mount within a mount can get at least some of the errors from the inner mount. Five logging functions are provided for this: (1) void logfc(struct fs_context *fc, const char *fmt, ...); This logs a message into the context. If the buffer is full, the earliest message is discarded. (2) void errorf(fc, fmt, ...); This wraps logfc() to log an error. (3) void invalf(fc, fmt, ...); This wraps errorf() and returns -EINVAL for convenience. (4) void warnf(fc, fmt, ...); This wraps logfc() to log a warning. (5) void infof(fc, fmt, ...); This wraps logfc() to log an informational message. Signed-off-by: David Howells Signed-off-by: Al Viro --- fs/fsopen.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 67 insertions(+) (limited to 'fs/fsopen.c') diff --git a/fs/fsopen.c b/fs/fsopen.c index d256f1ac9ff1..5fce6347de7a 100644 --- a/fs/fsopen.c +++ b/fs/fsopen.c @@ -20,6 +20,52 @@ #include #include "mount.h" +/* + * Allow the user to read back any error, warning or informational messages. + */ +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; + unsigned int logsize = ARRAY_SIZE(log->buffer); + ssize_t ret; + char *p; + 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; + } + + 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++; + mutex_unlock(&fc->uapi_mutex); + + 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; +} + static int fscontext_release(struct inode *inode, struct file *file) { struct fs_context *fc = file->private_data; @@ -32,6 +78,7 @@ static int fscontext_release(struct inode *inode, struct file *file) } const struct file_operations fscontext_fops = { + .read = fscontext_read, .release = fscontext_release, .llseek = no_llseek, }; @@ -50,6 +97,16 @@ static int fscontext_create_fd(struct fs_context *fc, unsigned int o_flags) return fd; } +static int fscontext_alloc_log(struct fs_context *fc) +{ + fc->log = kzalloc(sizeof(*fc->log), GFP_KERNEL); + if (!fc->log) + return -ENOMEM; + refcount_set(&fc->log->usage, 1); + fc->log->owner = fc->fs_type->owner; + return 0; +} + /* * Open a filesystem by name so that it can be configured for mounting. * @@ -62,6 +119,7 @@ SYSCALL_DEFINE2(fsopen, const char __user *, _fs_name, unsigned int, flags) struct file_system_type *fs_type; struct fs_context *fc; const char *fs_name; + int ret; if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN)) return -EPERM; @@ -84,5 +142,14 @@ SYSCALL_DEFINE2(fsopen, const char __user *, _fs_name, unsigned int, flags) return PTR_ERR(fc); fc->phase = FS_CONTEXT_CREATE_PARAMS; + + ret = fscontext_alloc_log(fc); + if (ret < 0) + goto err_fc; + return fscontext_create_fd(fc, flags & FSOPEN_CLOEXEC ? O_CLOEXEC : 0); + +err_fc: + put_fs_context(fc); + return ret; } -- cgit v1.2.3