[PATCHv2] kernel/panic: allocate taint string buffer dynamically

[Rio <rioo.tsukatsukii@gmail.com>]

The buffer used to hold the taint string is statically allocated, which
requires updating whenever a new taint flag is added.

Instead, allocate the exact required length at boot once the allocator is
available in an init function. The allocation sums the string lengths in
taint_flags[], along with space for separators and formatting.
print_tainted() is switched to use this dynamically allocated buffer.

If allocation fails, print_tainted() warns about the failure and continues
to use the original static buffer as a fallback.

Signed-off-by: Rio <rioo.tsukatsukii@gmail.com>
---
V1 -> V2: Allocate taint string buffer dynamically during init

v1: https://lore.kernel.org/all/20260220151500.13585-1-rioo.tsukatsukii@gmail.com/

 kernel/panic.c | 51 +++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 46 insertions(+), 5 deletions(-)

diff --git a/kernel/panic.c b/kernel/panic.c
index 75368738d32d..5d498ff8a18b 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -802,7 +802,7 @@ EXPORT_SYMBOL(panic);
  * small shell script that prints the TAINT_FLAGS_COUNT bits of
  * /proc/sys/kernel/tainted.
  *
- * Also, update TAINT_BUF_MAX below.
+ * Also, update INIT_TAINT_BUF_MAX below.
  */
 const struct taint_flag taint_flags[TAINT_FLAGS_COUNT] = {
 	TAINT_FLAG(PROPRIETARY_MODULE,		'P', 'G'),
@@ -856,17 +856,58 @@ static void print_tainted_seq(struct seq_buf *s, bool verbose)
 	}
 }
 
-/* 350 can accommodate all taint flags in verbose mode, with some headroom */
-#define TAINT_BUF_MAX 350
+/* The initial buffer can accommodate all taint flags in verbose
+ * mode, with some headroom. Once the allocator is available, the
+ * exact size is allocated dynamically; the initial buffer remains
+ * as a fallback if allocation fails.
+ *
+ * The verbose taint string currently requires up to 327 characters.
+ */
+#define INIT_TAINT_BUF_MAX 350
+
+static char init_taint_buf[INIT_TAINT_BUF_MAX];
+static char *taint_buf = init_taint_buf;
+static size_t taint_buf_size = INIT_TAINT_BUF_MAX;
+
+static __init int alloc_taint_buf(void)
+{
+	int i;
+	char *buf;
+	size_t size = 0;
+
+	size += sizeof("Tainted: ") - 1;
+	for (i = 0; i < TAINT_FLAGS_COUNT; i++) {
+		size += 2; /* For ", " */
+		size += 4; /* For "[%c]=" */
+		size += strlen(taint_flags[i].desc);
+	}
+
+	size += 1; /* For NULL terminator */
+
+	buf = kmalloc(size, GFP_KERNEL);
+
+	if (!buf) {
+		/* Allocation may fail; this warning explains possibly
+		 * truncated taint strings
+		 */
+		pr_warn_once("taint string buffer allocation failed, using fallback buffer\n");
+		return 0;
+	}
+
+	taint_buf = buf;
+	taint_buf_size = size;
+
+	return 0;
+}
+postcore_initcall(alloc_taint_buf);
 
 static const char *_print_tainted(bool verbose)
 {
-	static char buf[TAINT_BUF_MAX];
 	struct seq_buf s;
 
 	BUILD_BUG_ON(ARRAY_SIZE(taint_flags) != TAINT_FLAGS_COUNT);
 
-	seq_buf_init(&s, buf, sizeof(buf));
+	seq_buf_init(&s, taint_buf, taint_buf_size);
 
 	print_tainted_seq(&s, verbose);
 
-- 
2.52.0