Re: [PATCH v2] tracing: Limit access to parser->buffer when trace_get_user failed

[Pu Lehui]

On 2025/8/13 2:38, Steven Rostedt wrote:
On Wed,  6 Aug 2025 07:01:09 +0000
Pu Lehui <pule...@huaweicloud.com> wrote:

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4283ed4e8f59..138212f4ecde 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1814,9 +1814,11 @@ int trace_get_user(struct trace_parser *parser, const 
char __user *ubuf,
        if (!*ppos)
                trace_parser_clear(parser);
  
+	parser->fail = false;

This should be set when the parser is initialized.

Hi Steven,

parser->fail will always be set `false` when the parser is initialized, 
as trace_parser_get_init will do `memset(parser, 0, sizeof(*parser))`.

I will remove this in next.


+
        ret = get_user(ch, ubuf++);
        if (ret)
-               return ret;
+               goto fail;
  
  	read++;
        cnt--;
@@ -1830,7 +1832,7 @@ int trace_get_user(struct trace_parser *parser, const 
char __user *ubuf,
                while (cnt && isspace(ch)) {
                        ret = get_user(ch, ubuf++);
                        if (ret)
-                               return ret;
+                               goto fail;
                        read++;
                        cnt--;
                }
@@ -1848,12 +1850,14 @@ int trace_get_user(struct trace_parser *parser, const 
char __user *ubuf,
        while (cnt && !isspace(ch) && ch) {
                if (parser->idx < parser->size - 1)
                        parser->buffer[parser->idx++] = ch;
-               else
-                       return -EINVAL;
+               else {
+                       ret = -EINVAL;
+                       goto fail;
+               }
  
  		ret = get_user(ch, ubuf++);
                if (ret)
-                       return ret;
+                       goto fail;
                read++;
                cnt--;
        }
@@ -1868,11 +1872,15 @@ int trace_get_user(struct trace_parser *parser, const 
char __user *ubuf,
                /* Make sure the parsed string always terminates with '\0'. */
                parser->buffer[parser->idx] = 0;
        } else {
-               return -EINVAL;
+               ret = -EINVAL;
+               goto fail;
        }
  
  	*ppos += read;
        return read;
+fail:
+       parser->fail = true;

Should have a helper function called: trace_parser_fail(parser) and use
that.

Alright! Will make it next version.


-- Steve


+       return ret;
  }
  
  /* TODO add a seq_buf_to_buffer() */
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 1dbf1d3cf2f1..5072bb25a860 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1292,6 +1292,7 @@ bool ftrace_event_is_function(struct trace_event_call 
*call);
   */
  struct trace_parser {
        bool            cont;
+       bool            fail;
        char            *buffer;
        unsigned        idx;
        unsigned        size;
@@ -1299,7 +1300,7 @@ struct trace_parser {
  
  static inline bool trace_parser_loaded(struct trace_parser *parser)
  {
-       return (parser->idx != 0);
+       return !parser->fail && parser->idx != 0;
  }
  
  static inline bool trace_parser_cont(struct trace_parser *parser)