linux-kernel - [PATCH v2 1/3] kallsyms: avoid hardcoding the buffer size

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Date:   Fri,  6 May 2022 22:34:22 +0200
From:   Miguel Ojeda <ojeda@...nel.org>
To:     Boqun Feng <boqun.feng@...il.com>, Miguel Ojeda <ojeda@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Changbin Du <changbin.du@...el.com>,
        linux-kernel@...r.kernel.org
Cc:     rust-for-linux@...r.kernel.org
Subject: [PATCH v2 1/3] kallsyms: avoid hardcoding the buffer size

From: Boqun Feng <boqun.feng@...il.com>

This makes it easier to update the size later on.

Furthermore, a static assert is added to ensure both are updated
when that happens. The relationship used is one that keeps the new
size (512+1) close to the original buffer size (500).

Reviewed-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
Co-developed-by: Miguel Ojeda <ojeda@...nel.org>
Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
---
v2:
  - Collected Reviewed-by.
  - Use `sizeof(name)` in one instance, suggested by Kees Cook.

 scripts/kallsyms.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 8caabddf817c..82d6508bdf29 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -27,8 +27,18 @@
 
 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
 
+#define _stringify_1(x)	#x
+#define _stringify(x)	_stringify_1(x)
+
 #define KSYM_NAME_LEN		128
 
+/* A substantially bigger size than the current maximum. */
+#define KSYM_NAME_LEN_BUFFER	512
+_Static_assert(
+	KSYM_NAME_LEN_BUFFER == KSYM_NAME_LEN * 4,
+	"Please keep KSYM_NAME_LEN_BUFFER in sync with KSYM_NAME_LEN"
+);
+
 struct sym_entry {
 	unsigned long long addr;
 	unsigned int len;
@@ -197,15 +207,15 @@ static void check_symbol_range(const char *sym, unsigned long long addr,
 
 static struct sym_entry *read_symbol(FILE *in)
 {
-	char name[500], type;
+	char name[KSYM_NAME_LEN_BUFFER+1], type;
 	unsigned long long addr;
 	unsigned int len;
 	struct sym_entry *sym;
 	int rc;
 
-	rc = fscanf(in, "%llx %c %499s\n", &addr, &type, name);
+	rc = fscanf(in, "%llx %c %" _stringify(KSYM_NAME_LEN_BUFFER) "s\n", &addr, &type, name);
 	if (rc != 3) {
-		if (rc != EOF && fgets(name, 500, in) == NULL)
+		if (rc != EOF && fgets(name, sizeof(name), in) == NULL)
 			fprintf(stderr, "Read error or end of file.\n");
 		return NULL;
 	}
-- 
2.35.3