Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

1 files changed, 450 insertions, 0 deletions

diff --git a/fs/d_path.c b/fs/d_path.c
new file mode 100644
index 000000000..c25309006
--- /dev/null
+++ b/fs/d_path.c
@@ -0,0 +1,450 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/syscalls.h>
+#include <linux/export.h>
+#include <linux/uaccess.h>
+#include <linux/fs_struct.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/prefetch.h>
+#include "mount.h"
+#include "internal.h"
+
+struct prepend_buffer {
+	char *buf;
+	int len;
+};
+#define DECLARE_BUFFER(__name, __buf, __len) \
+	struct prepend_buffer __name = {.buf = __buf + __len, .len = __len}
+
+static char *extract_string(struct prepend_buffer *p)
+{
+	if (likely(p->len >= 0))
+		return p->buf;
+	return ERR_PTR(-ENAMETOOLONG);
+}
+
+static bool prepend_char(struct prepend_buffer *p, unsigned char c)
+{
+	if (likely(p->len > 0)) {
+		p->len--;
+		*--p->buf = c;
+		return true;
+	}
+	p->len = -1;
+	return false;
+}
+
+/*
+ * The source of the prepend data can be an optimistic load
+ * of a dentry name and length. And because we don't hold any
+ * locks, the length and the pointer to the name may not be
+ * in sync if a concurrent rename happens, and the kernel
+ * copy might fault as a result.
+ *
+ * The end result will correct itself when we check the
+ * rename sequence count, but we need to be able to handle
+ * the fault gracefully.
+ */
+static bool prepend_copy(void *dst, const void *src, int len)
+{
+	if (unlikely(copy_from_kernel_nofault(dst, src, len))) {
+		memset(dst, 'x', len);
+		return false;
+	}
+	return true;
+}
+
+static bool prepend(struct prepend_buffer *p, const char *str, int namelen)
+{
+	// Already overflowed?
+	if (p->len < 0)
+		return false;
+
+	// Will overflow?
+	if (p->len < namelen) {
+		// Fill as much as possible from the end of the name
+		str += namelen - p->len;
+		p->buf -= p->len;
+		prepend_copy(p->buf, str, p->len);
+		p->len = -1;
+		return false;
+	}
+
+	// Fits fully
+	p->len -= namelen;
+	p->buf -= namelen;
+	return prepend_copy(p->buf, str, namelen);
+}
+
+/**
+ * prepend_name - prepend a pathname in front of current buffer pointer
+ * @p: prepend buffer which contains buffer pointer and allocated length
+ * @name: name string and length qstr structure
+ *
+ * With RCU path tracing, it may race with d_move(). Use READ_ONCE() to
+ * make sure that either the old or the new name pointer and length are
+ * fetched. However, there may be mismatch between length and pointer.
+ * But since the length cannot be trusted, we need to copy the name very
+ * carefully when doing the prepend_copy(). It also prepends "/" at
+ * the beginning of the name. The sequence number check at the caller will
+ * retry it again when a d_move() does happen. So any garbage in the buffer
+ * due to mismatched pointer and length will be discarded.
+ *
+ * Load acquire is needed to make sure that we see the new name data even
+ * if we might get the length wrong.
+ */
+static bool prepend_name(struct prepend_buffer *p, const struct qstr *name)
+{
+	const char *dname = smp_load_acquire(&name->name); /* ^^^ */
+	u32 dlen = READ_ONCE(name->len);
+
+	return prepend(p, dname, dlen) && prepend_char(p, '/');
+}
+
+static int __prepend_path(const struct dentry *dentry, const struct mount *mnt,
+			  const struct path *root, struct prepend_buffer *p)
+{
+	while (dentry != root->dentry || &mnt->mnt != root->mnt) {
+		const struct dentry *parent = READ_ONCE(dentry->d_parent);
+
+		if (dentry == mnt->mnt.mnt_root) {
+			struct mount *m = READ_ONCE(mnt->mnt_parent);
+			struct mnt_namespace *mnt_ns;
+
+			if (likely(mnt != m)) {
+				dentry = READ_ONCE(mnt->mnt_mountpoint);
+				mnt = m;
+				continue;
+			}
+			/* Global root */
+			mnt_ns = READ_ONCE(mnt->mnt_ns);
+			/* open-coded is_mounted() to use local mnt_ns */
+			if (!IS_ERR_OR_NULL(mnt_ns) && !is_anon_ns(mnt_ns))
+				return 1;	// absolute root
+			else
+				return 2;	// detached or not attached yet
+		}
+
+		if (unlikely(dentry == parent))
+			/* Escaped? */
+			return 3;
+
+		prefetch(parent);
+		if (!prepend_name(p, &dentry->d_name))
+			break;
+		dentry = parent;
+	}
+	return 0;
+}
+
+/**
+ * prepend_path - Prepend path string to a buffer
+ * @path: the dentry/vfsmount to report
+ * @root: root vfsmnt/dentry
+ * @p: prepend buffer which contains buffer pointer and allocated length
+ *
+ * The function will first try to write out the pathname without taking any
+ * lock other than the RCU read lock to make sure that dentries won't go away.
+ * It only checks the sequence number of the global rename_lock as any change
+ * in the dentry's d_seq will be preceded by changes in the rename_lock
+ * sequence number. If the sequence number had been changed, it will restart
+ * the whole pathname back-tracing sequence again by taking the rename_lock.
+ * In this case, there is no need to take the RCU read lock as the recursive
+ * parent pointer references will keep the dentry chain alive as long as no
+ * rename operation is performed.
+ */
+static int prepend_path(const struct path *path,
+			const struct path *root,
+			struct prepend_buffer *p)
+{
+	unsigned seq, m_seq = 0;
+	struct prepend_buffer b;
+	int error;
+
+	rcu_read_lock();
+restart_mnt:
+	read_seqbegin_or_lock(&mount_lock, &m_seq);
+	seq = 0;
+	rcu_read_lock();
+restart:
+	b = *p;
+	read_seqbegin_or_lock(&rename_lock, &seq);
+	error = __prepend_path(path->dentry, real_mount(path->mnt), root, &b);
+	if (!(seq & 1))
+		rcu_read_unlock();
+	if (need_seqretry(&rename_lock, seq)) {
+		seq = 1;
+		goto restart;
+	}
+	done_seqretry(&rename_lock, seq);
+
+	if (!(m_seq & 1))
+		rcu_read_unlock();
+	if (need_seqretry(&mount_lock, m_seq)) {
+		m_seq = 1;
+		goto restart_mnt;
+	}
+	done_seqretry(&mount_lock, m_seq);
+
+	if (unlikely(error == 3))
+		b = *p;
+
+	if (b.len == p->len)
+		prepend_char(&b, '/');
+
+	*p = b;
+	return error;
+}
+
+/**
+ * __d_path - return the path of a dentry
+ * @path: the dentry/vfsmount to report
+ * @root: root vfsmnt/dentry
+ * @buf: buffer to return value in
+ * @buflen: buffer length
+ *
+ * Convert a dentry into an ASCII path name.
+ *
+ * Returns a pointer into the buffer or an error code if the
+ * path was too long.
+ *
+ * "buflen" should be positive.
+ *
+ * If the path is not reachable from the supplied root, return %NULL.
+ */
+char *__d_path(const struct path *path,
+	       const struct path *root,
+	       char *buf, int buflen)
+{
+	DECLARE_BUFFER(b, buf, buflen);
+
+	prepend_char(&b, 0);
+	if (unlikely(prepend_path(path, root, &b) > 0))
+		return NULL;
+	return extract_string(&b);
+}
+
+char *d_absolute_path(const struct path *path,
+	       char *buf, int buflen)
+{
+	struct path root = {};
+	DECLARE_BUFFER(b, buf, buflen);
+
+	prepend_char(&b, 0);
+	if (unlikely(prepend_path(path, &root, &b) > 1))
+		return ERR_PTR(-EINVAL);
+	return extract_string(&b);
+}
+
+static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
+{
+	unsigned seq;
+
+	do {
+		seq = read_seqbegin(&fs->seq);
+		*root = fs->root;
+	} while (read_seqretry(&fs->seq, seq));
+}
+
+/**
+ * d_path - return the path of a dentry
+ * @path: path to report
+ * @buf: buffer to return value in
+ * @buflen: buffer length
+ *
+ * Convert a dentry into an ASCII path name. If the entry has been deleted
+ * the string " (deleted)" is appended. Note that this is ambiguous.
+ *
+ * Returns a pointer into the buffer or an error code if the path was
+ * too long. Note: Callers should use the returned pointer, not the passed
+ * in buffer, to use the name! The implementation often starts at an offset
+ * into the buffer, and may leave 0 bytes at the start.
+ *
+ * "buflen" should be positive.
+ */
+char *d_path(const struct path *path, char *buf, int buflen)
+{
+	DECLARE_BUFFER(b, buf, buflen);
+	struct path root;
+
+	/*
+	 * We have various synthetic filesystems that never get mounted.  On
+	 * these filesystems dentries are never used for lookup purposes, and
+	 * thus don't need to be hashed.  They also don't need a name until a
+	 * user wants to identify the object in /proc/pid/fd/.  The little hack
+	 * below allows us to generate a name for these objects on demand:
+	 *
+	 * Some pseudo inodes are mountable.  When they are mounted
+	 * path->dentry == path->mnt->mnt_root.  In that case don't call d_dname
+	 * and instead have d_path return the mounted path.
+	 */
+	if (path->dentry->d_op && path->dentry->d_op->d_dname &&
+	    (!IS_ROOT(path->dentry) || path->dentry != path->mnt->mnt_root ||
+	     failfs_mnt(path->mnt)))
+		return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
+
+	rcu_read_lock();
+	get_fs_root_rcu(current->fs, &root);
+	if (unlikely(d_unlinked(path->dentry)))
+		prepend(&b, " (deleted)", 11);
+	else
+		prepend_char(&b, 0);
+	prepend_path(path, &root, &b);
+	rcu_read_unlock();
+
+	return extract_string(&b);
+}
+EXPORT_SYMBOL(d_path);
+
+/*
+ * Helper function for dentry_operations.d_dname() members
+ */
+char *dynamic_dname(char *buffer, int buflen, const char *fmt, ...)
+{
+	va_list args;
+	char *start;
+	int sz;
+
+	va_start(args, fmt);
+	sz = vsnprintf(buffer, buflen, fmt, args) + 1;
+	va_end(args);
+
+	if (sz > NAME_MAX || sz > buflen)
+		return ERR_PTR(-ENAMETOOLONG);
+
+	/* Move the formatted d_name to the end of the buffer. */
+	start = buffer + (buflen - sz);
+	return memmove(start, buffer, sz);
+}
+
+char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
+{
+	DECLARE_BUFFER(b, buffer, buflen);
+	/* these dentries are never renamed, so d_lock is not needed */
+	prepend(&b, " (deleted)", 11);
+	prepend(&b, dentry->d_name.name, dentry->d_name.len);
+	prepend_char(&b, '/');
+	return extract_string(&b);
+}
+
+/*
+ * Write full pathname from the root of the filesystem into the buffer.
+ */
+static char *__dentry_path(const struct dentry *d, struct prepend_buffer *p)
+{
+	const struct dentry *dentry;
+	struct prepend_buffer b;
+	int seq = 0;
+
+	rcu_read_lock();
+restart:
+	dentry = d;
+	b = *p;
+	read_seqbegin_or_lock(&rename_lock, &seq);
+	while (!IS_ROOT(dentry)) {
+		const struct dentry *parent = dentry->d_parent;
+
+		prefetch(parent);
+		if (!prepend_name(&b, &dentry->d_name))
+			break;
+		dentry = parent;
+	}
+	if (!(seq & 1))
+		rcu_read_unlock();
+	if (need_seqretry(&rename_lock, seq)) {
+		seq = 1;
+		goto restart;
+	}
+	done_seqretry(&rename_lock, seq);
+	if (b.len == p->len)
+		prepend_char(&b, '/');
+	return extract_string(&b);
+}
+
+char *dentry_path_raw(const struct dentry *dentry, char *buf, int buflen)
+{
+	DECLARE_BUFFER(b, buf, buflen);
+
+	prepend_char(&b, 0);
+	return __dentry_path(dentry, &b);
+}
+EXPORT_SYMBOL(dentry_path_raw);
+
+char *dentry_path(const struct dentry *dentry, char *buf, int buflen)
+{
+	DECLARE_BUFFER(b, buf, buflen);
+
+	if (unlikely(d_unlinked(dentry)))
+		prepend(&b, "//deleted", 10);
+	else
+		prepend_char(&b, 0);
+	return __dentry_path(dentry, &b);
+}
+
+static void get_fs_root_and_pwd_rcu(struct fs_struct *fs, struct path *root,
+				    struct path *pwd)
+{
+	unsigned seq;
+
+	do {
+		seq = read_seqbegin(&fs->seq);
+		*root = fs->root;
+		*pwd = fs->pwd;
+	} while (read_seqretry(&fs->seq, seq));
+}
+
+/*
+ * NOTE! The user-level library version returns a
+ * character pointer. The kernel system call just
+ * returns the length of the buffer filled (which
+ * includes the ending '\0' character), or a negative
+ * error value. So libc would do something like
+ *
+ *	char *getcwd(char * buf, size_t size)
+ *	{
+ *		int retval;
+ *
+ *		retval = sys_getcwd(buf, size);
+ *		if (retval >= 0)
+ *			return buf;
+ *		errno = -retval;
+ *		return NULL;
+ *	}
+ */
+SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
+{
+	int error;
+	struct path pwd, root;
+	char *page = __getname();
+
+	if (!page)
+		return -ENOMEM;
+
+	rcu_read_lock();
+	get_fs_root_and_pwd_rcu(current->fs, &root, &pwd);
+
+	if (unlikely(d_unlinked(pwd.dentry))) {
+		rcu_read_unlock();
+		error = -ENOENT;
+	} else {
+		unsigned len;
+		DECLARE_BUFFER(b, page, PATH_MAX);
+
+		prepend_char(&b, 0);
+		if (unlikely(prepend_path(&pwd, &root, &b) > 0))
+			prepend(&b, "(unreachable)", 13);
+		rcu_read_unlock();
+
+		len = PATH_MAX - b.len;
+		if (unlikely(len > PATH_MAX))
+			error = -ENAMETOOLONG;
+		else if (unlikely(len > size))
+			error = -ERANGE;
+		else if (copy_to_user(buf, b.buf, len))
+			error = -EFAULT;
+		else
+			error = len;
+	}
+	__putname(page);
+	return error;
+}