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Re: [Qemu-devel] [PATCH 1/2] trace: handle tracefs path truncation


From: Liam Merwick
Subject: Re: [Qemu-devel] [PATCH 1/2] trace: handle tracefs path truncation
Date: Thu, 21 Mar 2019 18:36:40 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0

On 21/03/2019 17:08, Stefan Hajnoczi wrote:
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 <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>


Reviewed-by: Liam Merwick <address@hidden>


---
  trace/ftrace.c | 12 ++++++++++--
  1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/trace/ftrace.c b/trace/ftrace.c
index 61692a8682..9749543d9b 100644
--- a/trace/ftrace.c
+++ b/trace/ftrace.c
@@ -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");





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