Commit fd985831 authored Mar 21, 2019 by Stefan Hajnoczi

trace: handle tracefs path truncation



If the tracefs mountpoint has a very long path we may exceed PATH_MAX.
This is a system misconfiguration and the user must resolve it so that
applications can perform path-based system calls successfully.

This issue does not occur on real-world systems since tracefs is mounted
on /sys/kernel/debug/tracing/, but the compiler is smart enough to
foresee the possibility and warn about the unchecked snprintf(3) return
value.  This patch fixes the compiler warning.

Reported-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Message-id: 20190321170831.6539-2-stefanha@redhat.com
Message-Id: <20190321170831.6539-2-stefanha@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

parent d97a39d9

trace/ftrace.c

+10 −2

Original line number	Diff line number	Diff line
		@@ -53,7 +53,11 @@ bool ftrace_init(void)
		}

		if (tracefs_found) {
		snprintf(path, PATH_MAX, "%s%s/tracing_on", mount_point, subdir);
		if (snprintf(path, PATH_MAX, "%s%s/tracing_on", mount_point, subdir)
		>= sizeof(path)) {
		fprintf(stderr, "Using tracefs mountpoint would exceed PATH_MAX\n");
		return false;
		}
		trace_fd = open(path, O_WRONLY);
		if (trace_fd < 0) {
		if (errno == EACCES) {
		@@ -72,7 +76,11 @@ bool ftrace_init(void)
		}
		close(trace_fd);
		}
		snprintf(path, PATH_MAX, "%s%s/trace_marker", mount_point, subdir);
		if (snprintf(path, PATH_MAX, "%s%s/trace_marker", mount_point, subdir)
		>= sizeof(path)) {
		fprintf(stderr, "Using tracefs mountpoint would exceed PATH_MAX\n");
		return false;
		}
		trace_marker_fd = open(path, O_WRONLY);
		if (trace_marker_fd < 0) {
		perror("Could not open ftrace 'trace_marker' file");