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tracing/filters: Support filtering for char * strings 

Usually, char * entries are dangerous in traces because the string
can be released whereas a pointer to it can still wait to be read from
the ring buffer.

But sometimes we can assume it's safe, like in case of RO data
(eg: __file__ or __line__, used in bkl trace event). If these RO data
are in a module and so is the call to the trace event, then it's safe,
because the ring buffer will be flushed once this module get unloaded.

To allow char * to be treated as a string:

	TRACE_EVENT(...,

		TP_STRUCT__entry(
			__field_ext(const char *, name, FILTER_PTR_STRING)
			...
		)

		...
	);

The filtering will not dereference "char *" unless the developer
explicitly sets FILTER_PTR_STR in __field_ext.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A7B9287.90205@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Li Zefan 2009-08-07 10:33:43 +08:00 committed by Steven Rostedt
parent 43b51ead3f
commit 87a342f5db
2 changed files with 24 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/ftrace_event.h
View File

@ -144,6 +144,7 @@ enum {
FILTER_OTHER = 0,
FILTER_STATIC_STRING,
FILTER_DYN_STRING,
FILTER_PTR_STRING,
};
extern int trace_define_field(struct ftrace_event_call *call,

26
kernel/trace/trace_events_filter.c
View File

@ -163,6 +163,20 @@ static int filter_pred_string(struct filter_pred *pred, void *event,
return match;
}
/* Filter predicate for char * pointers */
static int filter_pred_pchar(struct filter_pred *pred, void *event,
int val1, int val2)
{
char **addr = (char **)(event + pred->offset);
int cmp, match;
cmp = strncmp(*addr, pred->str_val, pred->str_len);
match = (!cmp) ^ pred->not;
return match;
}
/*
* Filter predicate for dynamic sized arrays of characters.
* These are implemented through a list of strings at the end
@ -489,7 +503,8 @@ int filter_assign_type(const char *type)
static bool is_string_field(struct ftrace_event_field *field)
{
return field->filter_type == FILTER_DYN_STRING ||
field->filter_type == FILTER_STATIC_STRING;
field->filter_type == FILTER_STATIC_STRING ||
field->filter_type == FILTER_PTR_STRING;
}
static int is_legal_op(struct ftrace_event_field *field, int op)
@ -579,11 +594,16 @@ static int filter_add_pred(struct filter_parse_state *ps,
}
if (is_string_field(field)) {
pred->str_len = field->size;
if (field->filter_type == FILTER_STATIC_STRING)
fn = filter_pred_string;
else
else if (field->filter_type == FILTER_DYN_STRING)
fn = filter_pred_strloc;
pred->str_len = field->size;
else {
fn = filter_pred_pchar;
pred->str_len = strlen(pred->str_val);
}
} else {
if (field->is_signed)
ret = strict_strtoll(pred->str_val, 0, &val);