[PATCH] tracing/probes: Treating longer symbol name on event comparation

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

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

MAX_COMMON_HEAD_LEN (63) was used to allocate a temporary buffer for
formatting command heads in trace_kprobe_match_command_head() and
trace_uprobe_match_command_head(). However, the buffer size is too
short for some longer symbols. Especially, with rust code, the symbol
can be mangled and become very long.

Refactor trace_kprobe_match_command_head() to perform direct string
comparisons using strcmp() and strncmp(), eliminating the need for a
temporary buffer and removing the MAX_COMMON_HEAD_LEN string length
restriction on probe symbol names.

For trace_uprobe_match_command_head(), since tu->filename is already
matched via strncmp(), use a fixed 64-byte stack buffer solely for
formatting offset and ref_ctr_offset (which requires at most 39 bytes).

With all users converted, remove the MAX_COMMON_HEAD_LEN definition from
trace_probe.h.

Reported-by: Zhan Xusheng <zhanxusheng1024@gmail.com>
Link: https://lore.kernel.org/all/20260724023317.624074-1-zhanxusheng@xiaomi.com/
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
base-commit: 5be3a9db600853578559681b2dd20a9bc7dd4fc5
---
 kernel/trace/trace_kprobe.c |   24 ++++++++++++++++--------
 kernel/trace/trace_probe.h  |    1 -
 kernel/trace/trace_uprobe.c |    2 +-
 3 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index c25f902aa1a6..e41a7c113646 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -149,20 +149,28 @@ static bool trace_kprobe_is_busy(struct dyn_event *ev)
 static bool trace_kprobe_match_command_head(struct trace_kprobe *tk,
 					    int argc, const char **argv)
 {
-	char buf[MAX_COMMON_HEAD_LEN + 1];
+	char buf[32];
+	int len;
 
 	if (!argc)
 		return true;
 
-	if (!tk->symbol)
+	if (!tk->symbol) {
 		snprintf(buf, sizeof(buf), "0x%p", tk->rp.kp.addr);
-	else if (tk->rp.kp.offset)
-		snprintf(buf, sizeof(buf), "%s+%u",
-			 trace_kprobe_symbol(tk), tk->rp.kp.offset);
-	else
-		snprintf(buf, sizeof(buf), "%s", trace_kprobe_symbol(tk));
-	if (strcmp(buf, argv[0]))
+		if (strcmp(buf, argv[0]))
+			return false;
+	} else if (tk->rp.kp.offset) {
+		len = strlen(trace_kprobe_symbol(tk));
+		if (strncmp(trace_kprobe_symbol(tk), argv[0], len) ||
+		    argv[0][len] != '+')
+			return false;
+
+		snprintf(buf, sizeof(buf), "%u", tk->rp.kp.offset);
+		if (strcmp(buf, &argv[0][len + 1]))
+			return false;
+	} else if (strcmp(trace_kprobe_symbol(tk), argv[0]))
 		return false;
+
 	argc--; argv++;
 
 	return trace_probe_match_command_args(&tk->tp, argc, argv);
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index c0f05763811c..fba1af092a9b 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -33,7 +33,6 @@
 
 #define MAX_TRACE_ARGS		128
 #define MAX_ARGSTR_LEN		255
-#define MAX_COMMON_HEAD_LEN	63
 #define MAX_ARRAY_LEN		64
 #define MAX_ARG_NAME_LEN	32
 #define MAX_BTF_ARGS_LEN	128
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 67bd8fd91e3e..861d857adadb 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -281,7 +281,7 @@ static bool trace_uprobe_is_busy(struct dyn_event *ev)
 static bool trace_uprobe_match_command_head(struct trace_uprobe *tu,
 					    int argc, const char **argv)
 {
-	char buf[MAX_COMMON_HEAD_LEN + 1];
+	char buf[64];
 	int len;
 
 	if (!argc)