linux-hardening - [PATCH] tracing: replace multiple deprecated strncpy with strscpy

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Message-ID: <20240930-strncpy-kernel-trace-trace_events_filter-c-v1-1-feed30820b83@google.com>
Date: Mon, 30 Sep 2024 17:03:45 -0700
From: Justin Stitt <justinstitt@...gle.com>
To: Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, Justin Stitt <justinstitt@...gle.com>, 
	Kees Cook <kees@...nel.org>
Subject: [PATCH] tracing: replace multiple deprecated strncpy with strscpy

strncpy() is deprecated for use on NUL-terminated destination strings [1] and
as such we should prefer more robust and less ambiguous string interfaces.

We expect the @pattern and @num_buf strings to be NUL-terminated, as
evidenced by their manual NUL-byte assignments immediately following
each copy.

Switch to using strscpy which guarantees NUL-termination for the
destination buffer -- eschewing manual NUL-byte assignments. strscpy
does not NUL-pad so to keep this behavior zero-allocate @num_buf. @pred
is already zero-allocated before the copies.
	pred = kzalloc(sizeof(*pred), GFP_KERNEL);

This should result in no behavioral changes whilst helping towards the
goal of [2] -- with the ultimate goal of removing strncpy in favor of
less ambiguous and more robust alternatives.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90 [2]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
Cc: Kees Cook <keescook@...omium.org>
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
 kernel/trace/trace_events_filter.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 0c611b281a5b..76b55eead8ac 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1506,7 +1506,7 @@ static int parse_pred(const char *str, void *data,
 	unsigned long offset;
 	unsigned long size;
 	unsigned long ip;
-	char num_buf[24];	/* Big enough to hold an address */
+	char num_buf[24] = {0};	/* Big enough to hold an address */
 	char *field_name;
 	char *name;
 	bool function = false;
@@ -1616,8 +1616,7 @@ static int parse_pred(const char *str, void *data,
 				goto err_free;
 			}
 
-			strncpy(num_buf, str + s, len);
-			num_buf[len] = 0;
+			strscpy(num_buf, str + s, len);
 
 			ret = kstrtoul(num_buf, 0, &ip);
 			if (ret) {
@@ -1694,8 +1693,7 @@ static int parse_pred(const char *str, void *data,
 		if (!pred->regex)
 			goto err_mem;
 		pred->regex->len = len;
-		strncpy(pred->regex->pattern, str + s, len);
-		pred->regex->pattern[len] = 0;
+		strscpy(pred->regex->pattern, str + s, len);
 
 	} else if (!strncmp(str + i, "CPUS", 4)) {
 		unsigned int maskstart;
@@ -1859,8 +1857,7 @@ static int parse_pred(const char *str, void *data,
 		if (!pred->regex)
 			goto err_mem;
 		pred->regex->len = len;
-		strncpy(pred->regex->pattern, str + s, len);
-		pred->regex->pattern[len] = 0;
+		strscpy(pred->regex->pattern, str + s, len);
 
 		filter_build_regex(pred);
 
@@ -1919,8 +1916,7 @@ static int parse_pred(const char *str, void *data,
 			goto err_free;
 		}
 
-		strncpy(num_buf, str + s, len);
-		num_buf[len] = 0;
+		strscpy(num_buf, str + s, len);
 
 		/* Make sure it is a value */
 		if (field->is_signed)

---
base-commit: bc83b4d1f08695e85e85d36f7b803da58010161d
change-id: 20240930-strncpy-kernel-trace-trace_events_filter-c-f44a3f848518

Best regards,
--
Justin Stitt <justinstitt@...gle.com>