netdev - [PATCH ethtool] json_print: add NULL check before jsonw_string_field() in print

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Message-Id: <20250516204005.260753-1-ant.v.moryakov@gmail.com>
Date: Fri, 16 May 2025 23:40:05 +0300
From: ant.v.moryakov@...il.com
To: mkubecek@...e.cz
Cc: netdev@...r.kernel.org,
	AntonMoryakov <ant.v.moryakov@...il.com>
Subject: [PATCH ethtool] json_print: add NULL check before jsonw_string_field() in print_string()

From: AntonMoryakov <ant.v.moryakov@...il.com>

Static analyzer (Svace) reported a potential null pointer dereference
in print_string(). Specifically, when both 'key' and 'value' are NULL,
the function falls through to jsonw_string_field(_jw, key, value),
which dereferences both pointers.

Although comments suggest this case is unlikely, it is safer to
explicitly guard against it. This patch adds a check to ensure
both key and value are non-NULL before passing to jsonw_string_field().

This resolves:
DEREF_AFTER_NULL: json_print.c:142

Found by Svace static analysis tool.

Signed-off-by: Anton Moryakov <ant.v.moryakov@...il.com>

---
 json_print.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/json_print.c b/json_print.c
index 4f62767..76e654b 100644
--- a/json_print.c
+++ b/json_print.c
@@ -138,13 +138,15 @@ void print_string(enum output_type type,
 			jsonw_name(_jw, key);
 		else if (!key && value)
 			jsonw_string(_jw, value);
-		else
+		else if (key && value)
 			jsonw_string_field(_jw, key, value);
 	} else if (_IS_FP_CONTEXT(type)) {
-		fprintf(stdout, fmt, value);
+		if (value)  // защита fprintf
+			fprintf(stdout, fmt, value);
 	}
 }
 
+
 /*
  * value's type is bool. When using this function in FP context you can't pass
  * a value to it, you will need to use "is_json_context()" to have different
-- 
2.34.1