tracing/probes: Avoid temporary buffer truncation in trace_probe_match_command_args()

commit 15f1978 upstream.

In trace_probe_match_command_args(), a stack buffer buf[MAX_ARGSTR_LEN + 1]
(256 bytes) is used to format "<name>=<comm>". However, since name can
be up to 32 bytes (MAX_ARG_NAME_LEN) and comm up to 255 bytes
(MAX_ARGSTR_LEN), the formatted string can exceed 256 bytes and get
truncated by snprintf(), causing spurious argument matching failures.

Instead of formatting into a temporary buffer on stack, compare the
argument name, the '=' delimiter, and the comm expression directly.

Link: https://lore.kernel.org/all/178454233010.290363.10428767141343428804.stgit@devnote2/

Fixes: eb5bf81 ("tracing/kprobe: Add per-probe delete from event")
Cc: stable@vger.kernel.org
Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: mhiramat

kernel/trace/trace_probe.c

@@ -2105,16 +2105,17 @@ int trace_probe_compare_arg_type(struct trace_probe *a, struct trace_probe *b)
 bool trace_probe_match_command_args(struct trace_probe *tp,
 				    int argc, const char **argv)
 {
-	char buf[MAX_ARGSTR_LEN + 1];
 	int i;
 
 	if (tp->nr_args < argc)
 		return false;
 
 	for (i = 0; i < argc; i++) {
-		snprintf(buf, sizeof(buf), "%s=%s",
-			 tp->args[i].name, tp->args[i].comm);
-		if (strcmp(buf, argv[i]))
+		int len = strlen(tp->args[i].name);
+
+		if (strncmp(argv[i], tp->args[i].name, len) ||
+		    argv[i][len] != '=' ||
+		    strcmp(argv[i] + len + 1, tp->args[i].comm))
 			return false;
 	}
 	return true;