linux-kernel - [PATCH v3] checkpatch: add uninitialized pointer with _

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Message-Id: <20251025-aheev-checkpatch-uninitialized-free-v3-1-a67f72b1c2bd@gmail.com>
Date: Sat, 25 Oct 2025 13:26:16 +0530
From: Ally Heev <allyheev@...il.com>
To: Dwaipayan Ray <dwaipayanray1@...il.com>, 
 Lukas Bulwahn <lukas.bulwahn@...il.com>, Joe Perches <joe@...ches.com>, 
 Jonathan Corbet <corbet@....net>, Andy Whitcroft <apw@...onical.com>
Cc: workflows@...r.kernel.org, linux-doc@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Dan Carpenter <dan.carpenter@...aro.org>, 
 David Hunter <david.hunter.linux@...il.com>, 
 Shuah Khan <skhan@...uxfoundation.org>, Viresh Kumar <vireshk@...nel.org>, 
 Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>, 
 linux-pm <linux-pm@...r.kernel.org>, dan.j.williams@...el.com, 
 Ally Heev <allyheev@...il.com>
Subject: [PATCH v3] checkpatch: add uninitialized pointer with __free
 attribute check

uninitialized pointers with __free attribute can cause undefined
behaviour as the memory allocated to the pointer is freed
automatically when the pointer goes out of scope.
add check in checkpatch to detect such issues

Suggested-by: Dan Carpenter <dan.carpenter@...aro.org>
Link: https://lore.kernel.org/all/8a4c0b43-cf63-400d-b33d-d9c447b7e0b9@suswa.mountain/
Acked-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Ally Heev <allyheev@...il.com>
---
Testing:
ran checkpatch.pl before and after the change on 
crypto/asymmetric_keys/x509_public_key.c, which has
both initialized with NULL and uninitialized pointers
---
Changes in v3:
- remove $FreeAttribute
- Link to v2: https://lore.kernel.org/r/20251024-aheev-checkpatch-uninitialized-free-v2-0-16c0900e8130@gmail.com

Changes in v2:
- change cover letter and title to reflect new changes
- fix regex to handle multiple declarations in a single line case
- convert WARN to ERROR for uninitialized pointers
- add a new WARN for pointers initialized with NULL 
- NOTE: tried handling multiple declarations on a single line by splitting
        them and matching the parts with regex, but, it turned out to be 
	complex and overkill. Moreover, multi-line declarations pose a threat
- Link to v1: https://lore.kernel.org/r/20251021-aheev-checkpatch-uninitialized-free-v1-1-18fb01bc6a7a@gmail.com
---
 Documentation/dev-tools/checkpatch.rst | 5 +++++
 scripts/checkpatch.pl                  | 6 ++++++
 2 files changed, 11 insertions(+)

diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
index d5c47e560324fb2399a5b1bc99c891ed1de10535..1a304bf38bcd27e50bbb7cd4383b07ac54d20b0a 100644
--- a/Documentation/dev-tools/checkpatch.rst
+++ b/Documentation/dev-tools/checkpatch.rst
@@ -1009,6 +1009,11 @@ Functions and Variables
 
       return bar;
 
+  **UNINITIALIZED_PTR_WITH_FREE**
+    Pointers with __free attribute should be initialized. Not doing so
+    may lead to undefined behavior as the memory allocated (garbage,
+    in case not initialized) to the pointer is freed automatically
+    when the pointer goes out of scope.
 
 Permissions
 -----------
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 92669904eecc7a8d2afd3f2625528e02b6d17cd6..e697d81d71c0b3628f7b59807e8bc40d582621bb 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -7721,6 +7721,12 @@ sub process {
 				ERROR("MISSING_SENTINEL", "missing sentinel in ID array\n" . "$here\n$stat\n");
 			}
 		}
+
+# check for uninitialized pointers with __free attribute
+		while ($line =~ /\*\s*($Ident)\s+__free\s*\(\s*$Ident\s*\)\s*[,;]/g) {
+			ERROR("UNINITIALIZED_PTR_WITH_FREE",
+			      "pointer '$1' with __free attribute should be initialized\n" . $herecurr);
+		}
 	}
 
 	# If we have no input at all, then there is nothing to report on

---
base-commit: 6548d364a3e850326831799d7e3ea2d7bb97ba08
change-id: 20251021-aheev-checkpatch-uninitialized-free-5c39f75e10a1

Best regards,
-- 
Ally Heev <allyheev@...il.com>