thunderbolt: Fix NULL dereference in tb_remove_work()grafted

There is a slight race between tb_remove_work() and tb_domain_remove()
which leads to dereferencing a NULL tb->root_switch pointer inside
tb_free_unplugged_xdomains():

        Thread A                            Thread B

  tb_remove_work()
                                    tb_domain_remove()
                                      mutex_lock(&tb->lock)
                                      tb_stop()
                                        /* doesn't cancel a running callback */
                                        cancel_delayed_work(&tcm->remove_work)
                                        ...
                                        tb_switch_remove(tb->root_switch)
                                        tb->root_switch = NULL
                                      mutex_unlock(&tb->lock)
    mutex_lock(&tb->lock)
    ...
    /* without checking ->root_switch */
    tb_free_unplugged_xdomains(tb->root_switch)
    mutex_unlock(&tb->lock)

Commit a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without
holding tb->lock") doesn't seem right to move tb_free_unplugged_xdomains()
out of the &tb->lock section and the check for tb->root_switch, in
particular.  It states:

  For this reason separate removing the XDomain from the topology data
  structures (where we need the lock) from unregistering the device from
  the bus (where remove callbacks of the drivers are being called).

tb_free_unplugged_xdomains() belongs to the former group of functions
requiring the lock.  And it also calls tb_xdomain_remove() which should
only be called with &tb->lock held.

Found by Linux Verification Center (linuxtesting.org) with Svace static
analysis tool.

Fixes: a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without holding tb->lock")
Cc: stable@vger.kernel.org
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

1 files changed, 218 insertions, 0 deletions

diff --git a/tools/lib/subcmd/exec-cmd.c b/tools/lib/subcmd/exec-cmd.c
new file mode 100644
index 000000000..7739b5217
--- /dev/null
+++ b/tools/lib/subcmd/exec-cmd.c
@@ -0,0 +1,218 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/compiler.h>
+#include <linux/string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include "subcmd-util.h"
+#include "exec-cmd.h"
+#include "subcmd-config.h"
+
+#define MAX_ARGS	32
+#define PATH_MAX	4096
+
+static const char *argv_exec_path;
+static const char *argv0_path;
+
+void exec_cmd_init(const char *exec_name, const char *prefix,
+		   const char *exec_path, const char *exec_path_env)
+{
+	subcmd_config.exec_name		= exec_name;
+	subcmd_config.prefix		= prefix;
+	subcmd_config.exec_path		= exec_path;
+	subcmd_config.exec_path_env	= exec_path_env;
+
+	/* Setup environment variable for invoked shell script. */
+	setenv("PREFIX", prefix, 1);
+}
+
+#define is_dir_sep(c) ((c) == '/')
+
+static int is_absolute_path(const char *path)
+{
+	return path[0] == '/';
+}
+
+static const char *get_pwd_cwd(char *buf, size_t sz)
+{
+	char *pwd;
+	struct stat cwd_stat, pwd_stat;
+	if (getcwd(buf, sz) == NULL)
+		return NULL;
+	pwd = getenv("PWD");
+	if (pwd && strcmp(pwd, buf)) {
+		stat(buf, &cwd_stat);
+		if (!stat(pwd, &pwd_stat) &&
+		    pwd_stat.st_dev == cwd_stat.st_dev &&
+		    pwd_stat.st_ino == cwd_stat.st_ino) {
+			strlcpy(buf, pwd, sz);
+		}
+	}
+	return buf;
+}
+
+static const char *make_nonrelative_path(char *buf, size_t sz, const char *path)
+{
+	if (is_absolute_path(path)) {
+		if (strlcpy(buf, path, sz) >= sz)
+			die("Too long path: %.*s", 60, path);
+	} else {
+		const char *cwd = get_pwd_cwd(buf, sz);
+
+		if (!cwd)
+			die("Cannot determine the current working directory");
+
+		if (strlen(cwd) + strlen(path) + 2 >= sz)
+			die("Too long path: %.*s", 60, path);
+
+		strcat(buf, "/");
+		strcat(buf, path);
+	}
+	return buf;
+}
+
+char *system_path(const char *path)
+{
+	char *buf = NULL;
+
+	if (is_absolute_path(path))
+		return strdup(path);
+
+	astrcatf(&buf, "%s/%s", subcmd_config.prefix, path);
+
+	return buf;
+}
+
+const char *extract_argv0_path(const char *argv0)
+{
+	const char *slash;
+
+	if (!argv0 || !*argv0)
+		return NULL;
+	slash = argv0 + strlen(argv0);
+
+	while (argv0 <= slash && !is_dir_sep(*slash))
+		slash--;
+
+	if (slash >= argv0) {
+		argv0_path = strndup(argv0, slash - argv0);
+		return argv0_path ? slash + 1 : NULL;
+	}
+
+	return argv0;
+}
+
+void set_argv_exec_path(const char *exec_path)
+{
+	argv_exec_path = exec_path;
+	/*
+	 * Propagate this setting to external programs.
+	 */
+	setenv(subcmd_config.exec_path_env, exec_path, 1);
+}
+
+
+/* Returns the highest-priority location to look for subprograms. */
+char *get_argv_exec_path(void)
+{
+	char *env;
+
+	if (argv_exec_path)
+		return strdup(argv_exec_path);
+
+	env = getenv(subcmd_config.exec_path_env);
+	if (env && *env)
+		return strdup(env);
+
+	return system_path(subcmd_config.exec_path);
+}
+
+static void add_path(char **out, const char *path)
+{
+	if (path && *path) {
+		if (is_absolute_path(path))
+			astrcat(out, path);
+		else {
+			char buf[PATH_MAX];
+
+			astrcat(out, make_nonrelative_path(buf, sizeof(buf), path));
+		}
+
+		astrcat(out, ":");
+	}
+}
+
+void setup_path(void)
+{
+	const char *old_path = getenv("PATH");
+	char *new_path = NULL;
+	char *tmp = get_argv_exec_path();
+
+	add_path(&new_path, tmp);
+	add_path(&new_path, argv0_path);
+	free(tmp);
+
+	if (old_path)
+		astrcat(&new_path, old_path);
+	else
+		astrcat(&new_path, "/usr/local/bin:/usr/bin:/bin");
+
+	setenv("PATH", new_path, 1);
+
+	free(new_path);
+}
+
+static const char **prepare_exec_cmd(const char **argv)
+{
+	int argc;
+	const char **nargv;
+
+	for (argc = 0; argv[argc]; argc++)
+		; /* just counting */
+	nargv = malloc(sizeof(*nargv) * (argc + 2));
+
+	nargv[0] = subcmd_config.exec_name;
+	for (argc = 0; argv[argc]; argc++)
+		nargv[argc + 1] = argv[argc];
+	nargv[argc + 1] = NULL;
+	return nargv;
+}
+
+int execv_cmd(const char **argv) {
+	const char **nargv = prepare_exec_cmd(argv);
+
+	/* execvp() can only ever return if it fails */
+	execvp(subcmd_config.exec_name, (char **)nargv);
+
+	free(nargv);
+	return -1;
+}
+
+
+int execl_cmd(const char *cmd,...)
+{
+	int argc;
+	const char *argv[MAX_ARGS + 1];
+	const char *arg;
+	va_list param;
+
+	va_start(param, cmd);
+	argv[0] = cmd;
+	argc = 1;
+	while (argc < MAX_ARGS) {
+		arg = argv[argc++] = va_arg(param, char *);
+		if (!arg)
+			break;
+	}
+	va_end(param);
+	if (MAX_ARGS <= argc) {
+		fprintf(stderr, " Error: too many args to run %s\n", cmd);
+		return -1;
+	}
+
+	argv[argc] = NULL;
+	return execv_cmd(argv);
+}