On Fri, 18 Jul 2025 13:46:27 -0400
Steven Rostedt [off-list ref] wrote:

On Fri, 18 Jul 2025 20:34:29 +0900
"Masami Hiramatsu (Google)" [off-list ref] wrote:

quoted

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Allocate temporary string buffers for parsing kprobe-events
from heap instead of stack.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 kernel/trace/trace_kprobe.c |   39 +++++++++++++++++++++++++--------------
 1 file changed, 25 insertions(+), 14 deletions(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 15d7a381a128..793af6000f16 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c

@@ -861,20 +861,20 @@ static int trace_kprobe_create_internal(int argc, const char *argv[],
 	 *  FETCHARG:TYPE : use TYPE instead of unsigned long.
 	 */
 	struct trace_kprobe *tk __free(free_trace_kprobe) = NULL;
+	const char *event = NULL, *group = KPROBE_EVENT_SYSTEM;
+	const char **new_argv __free(kfree) = NULL;
 	int i, len, new_argc = 0, ret = 0;
-	bool is_return = false;
 	char *symbol __free(kfree) = NULL;
-	char *tmp = NULL;
-	const char **new_argv __free(kfree) = NULL;
-	const char *event = NULL, *group = KPROBE_EVENT_SYSTEM;
+	char *ebuf __free(kfree) = NULL;
+	char *gbuf __free(kfree) = NULL;
+	char *abuf __free(kfree) = NULL;
+	char *dbuf __free(kfree) = NULL;
 	enum probe_print_type ptype;
+	bool is_return = false;
 	int maxactive = 0;
-	long offset = 0;
 	void *addr = NULL;
-	char buf[MAX_EVENT_NAME_LEN];
-	char gbuf[MAX_EVENT_NAME_LEN];
-	char abuf[MAX_BTF_ARGS_LEN];
-	char *dbuf __free(kfree) = NULL;
+	char *tmp = NULL;
+	long offset = 0;
 
 	switch (argv[0][0]) {
 	case 'r':

@@ -893,6 +893,8 @@ static int trace_kprobe_create_internal(int argc, const char *argv[],
 		event++;
 
 	if (isdigit(argv[0][1])) {
+		char *buf __free(kfree) = NULL;

So this gets freed when this if block ends, right?

Yes, because in this block, "buf" is used as a really temporary
buffer.

quoted

+
 		if (!is_return) {
 			trace_probe_log_err(1, BAD_MAXACT_TYPE);
 			return -EINVAL;

@@ -905,7 +907,7 @@ static int trace_kprobe_create_internal(int argc, const char *argv[],
 			trace_probe_log_err(1, BAD_MAXACT);
 			return -EINVAL;
 		}
-		memcpy(buf, &argv[0][1], len);
+		buf = kmemdup(&argv[0][1], len + 1, GFP_KERNEL);
 		buf[len] = '\0';
 		ret = kstrtouint(buf, 0, &maxactive);
 		if (ret || !maxactive) {

@@ -973,6 +975,9 @@ static int trace_kprobe_create_internal(int argc, const char *argv[],
 
 	trace_probe_log_set_index(0);
 	if (event) {
+		gbuf = kmalloc(MAX_EVENT_NAME_LEN, GFP_KERNEL);
+		if (!gbuf)
+			return -ENOMEM;
 		ret = traceprobe_parse_event_name(&event, &group, gbuf,
 						  event - argv[0]);

And you can't use the same trick here because
traceprobe_parse_event_name() assigns "group" to gbuf and is used
outside this if block.

Yes, that holds the group name used until parsing the probe.

I notice there's no comment that states this. At the very minimum,
traceprobe_parse_event_name() should have a kerneldoc comment above its
definition and state this.

Yeah, that function should be docummented, it is a bit complicated.

But that's not an issue with this patch
series. Just an observation. Thus...

Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Thank you!

-- Steve

quoted

 		if (ret)

@@ -981,16 +986,22 @@ static int trace_kprobe_create_internal(int argc, const char *argv[],
 
 	if (!event) {
 		/* Make a new event name */
+		ebuf = kmalloc(MAX_EVENT_NAME_LEN, GFP_KERNEL);
+		if (!ebuf)
+			return -ENOMEM;
 		if (symbol)
-			snprintf(buf, MAX_EVENT_NAME_LEN, "%c_%s_%ld",
+			snprintf(ebuf, MAX_EVENT_NAME_LEN, "%c_%s_%ld",
 				 is_return ? 'r' : 'p', symbol, offset);
 		else
-			snprintf(buf, MAX_EVENT_NAME_LEN, "%c_0x%p",
+			snprintf(ebuf, MAX_EVENT_NAME_LEN, "%c_0x%p",
 				 is_return ? 'r' : 'p', addr);
-		sanitize_event_name(buf);
-		event = buf;
+		sanitize_event_name(ebuf);
+		event = ebuf;
 	}
 
+	abuf = kmalloc(MAX_BTF_ARGS_LEN, GFP_KERNEL);
+	if (!abuf)
+		return -ENOMEM;
 	argc -= 2; argv += 2;
 	ctx->funcname = symbol;
 	new_argv = traceprobe_expand_meta_args(argc, argv, &new_argc,

-- 
Masami Hiramatsu (Google) [off-list ref]