uninitialized pointers with __free attribute can cause undefined
behavior as the memory randomly assigned 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@linaro.org>
Link: https://lore.kernel.org/all/8a4c0b43-cf63-400d-b33d-d9c447b7e0b9@suswa.mountain/
Link: https://lore.kernel.org/all/58fd478f408a34b578ee8d949c5c4b4da4d4f41d.camel@HansenPartnership.com/
Acked-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Ally Heev <allyheev@gmail.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 v5:
- fixed checkpatch doc
- Link to v4: https://lore.kernel.org/r/20251107-aheev-checkpatch-uninitialized-free-v4-1-4822a6ac728f@gmail.com

Changes in v4:
- fixed UNINITIALIZED_PTR_WITH_FREE description 
- Link to v3: https://lore.kernel.org/r/20251025-aheev-checkpatch-uninitialized-free-v3-1-a67f72b1c2bd@gmail.com

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 | 20 ++++++++++++++++++++
 scripts/checkpatch.pl                  |  6 ++++++
 2 files changed, 26 insertions(+)

diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
index d5c47e560324fb2399a5b1bc99c891ed1de10535..865aaaf6dc51b1c3f763b3cbb8713da3d00db960 100644
--- a/Documentation/dev-tools/checkpatch.rst
+++ b/Documentation/dev-tools/checkpatch.rst
@@ -1009,6 +1009,26 @@ Functions and Variables
 
       return bar;
 
+  **UNINITIALIZED_PTR_WITH_FREE**
+    Pointers with __free attribute should be defined and assigned in one
+    statement. In this case declarations at the top of the function rule
+    can be relaxed. Not doing so may lead to undefined behavior as the
+    memory assigned (garbage, in case not initialized) to the pointer is
+    freed automatically when the pointer goes out of scope.
+
+    See: https://lore.kernel.org/lkml/58fd478f408a34b578ee8d949c5c4b4da4d4f41d.camel@HansenPartnership.com/
+
+    Example::
+
+      type var __free(free_func);
+      ... // function might have returned here
+      var = malloc(var_size);
+
+    should be initialized as::
+
+      type var __free(free_func) = malloc(var_size);
+      ... // return here would just free allocated memory
+
 
 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@gmail.com>

On 24/11/2025 15:44, Ally Heev wrote:
> uninitialized pointers with __free attribute can cause undefined
> behavior as the memory randomly assigned 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@linaro.org>
> Link: https://lore.kernel.org/all/8a4c0b43-cf63-400d-b33d-d9c447b7e0b9@suswa.mountain/
> Link: https://lore.kernel.org/all/58fd478f408a34b578ee8d949c5c4b4da4d4f41d.camel@HansenPartnership.com/
> Acked-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Ally Heev <allyheev@gmail.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 v5:
> - fixed checkpatch doc
> - Link to v4: https://lore.kernel.org/r/20251107-aheev-checkpatch-uninitialized-free-v4-1-4822a6ac728f@gmail.com
> 
> Changes in v4:
> - fixed UNINITIALIZED_PTR_WITH_FREE description 
> - Link to v3: https://lore.kernel.org/r/20251025-aheev-checkpatch-uninitialized-free-v3-1-a67f72b1c2bd@gmail.com
> 
> 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 | 20 ++++++++++++++++++++
>  scripts/checkpatch.pl                  |  6 ++++++
>  2 files changed, 26 insertions(+)
> 
> diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
> index d5c47e560324fb2399a5b1bc99c891ed1de10535..865aaaf6dc51b1c3f763b3cbb8713da3d00db960 100644
> --- a/Documentation/dev-tools/checkpatch.rst
> +++ b/Documentation/dev-tools/checkpatch.rst
> @@ -1009,6 +1009,26 @@ Functions and Variables
>  
>        return bar;
>  
> +  **UNINITIALIZED_PTR_WITH_FREE**
> +    Pointers with __free attribute should be defined and assigned in one

You did not implement my proposal fully. I wanted to express that their
declaration should be in the place of use, meaning first use.

> +    statement. In this case declarations at the top of the function rule

This does not solve it, because one can declare, define and assign in
top part of the function not achieving what we want - place of use.

Not sure if it is worth debating on, so overall (although I did not
verify regex very thoroughly):

Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>

Best regards,
Krzysztof