[PATCH v7] checkpatch: add uninitialized pointer with __free attribute check

[PATCH v7] checkpatch: add uninitialized pointer with __free attribute check

[Ally Heev]

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>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
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 v7:
- RESEND. Also, added Reviewed-by trailer
- Link to v6: https://lore.kernel.org/r/20251125-aheev-checkpatch-uninitialized-free-v6-1-2f3a1d78f678@gmail.com

Changes in v6:
- added declaration at the place of use suggestion
- Link to v5: https://lore.kernel.org/r/20251124-aheev-checkpatch-uninitialized-free-v5-1-0c523b1a3f5a@gmail.com

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 | 23 +++++++++++++++++++++++
 scripts/checkpatch.pl                  |  6 ++++++
 2 files changed, 29 insertions(+)

diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
index d5c47e560324fb2399a5b1bc99c891ed1de10535..b6e02fb91e85710fecfc0a5e5c83a8e7f32d1d3c 100644
--- a/Documentation/dev-tools/checkpatch.rst
+++ b/Documentation/dev-tools/checkpatch.rst
@@ -1009,6 +1009,29 @@ Functions and Variables
 
       return bar;
 
+  **UNINITIALIZED_PTR_WITH_FREE**
+    Pointers with __free attribute should be declared at the place of use
+    and initialized (see include/linux/cleanup.h). 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.
+
+    Also see: https://lore.kernel.org/lkml/58fd478f408a34b578ee8d949c5c4b4da4d4f41d.camel@HansenPartnership.com/
+
+    Example::
+
+      type var __free(free_func);
+      ... // var not used, but, in future someone might add a return here
+      var = malloc(var_size);
+      ...
+
+    should be initialized as::
+
+      ...
+      type var __free(free_func) = malloc(var_size);
+      ...
+
 
 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>

Re: [PATCH v7] checkpatch: add uninitialized pointer with __free attribute check

[Joe Perches]

On Wed, 2025-12-03 at 20:58 +0530, 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>
> Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
> Signed-off-by: Ally Heev <allyheev@gmail.com>

Acked-by: Joe Perches <joe@perches.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 v7:
> - RESEND. Also, added Reviewed-by trailer
> - Link to v6: https://lore.kernel.org/r/20251125-aheev-checkpatch-uninitialized-free-v6-1-2f3a1d78f678@gmail.com
> 
> Changes in v6:
> - added declaration at the place of use suggestion
> - Link to v5: https://lore.kernel.org/r/20251124-aheev-checkpatch-uninitialized-free-v5-1-0c523b1a3f5a@gmail.com
> 
> 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 | 23 +++++++++++++++++++++++
>  scripts/checkpatch.pl                  |  6 ++++++
>  2 files changed, 29 insertions(+)
> 
> diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
> index d5c47e560324fb2399a5b1bc99c891ed1de10535..b6e02fb91e85710fecfc0a5e5c83a8e7f32d1d3c 100644
> --- a/Documentation/dev-tools/checkpatch.rst
> +++ b/Documentation/dev-tools/checkpatch.rst
> @@ -1009,6 +1009,29 @@ Functions and Variables
>  
>        return bar;
>  
> +  **UNINITIALIZED_PTR_WITH_FREE**
> +    Pointers with __free attribute should be declared at the place of use
> +    and initialized (see include/linux/cleanup.h). 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.
> +
> +    Also see: https://lore.kernel.org/lkml/58fd478f408a34b578ee8d949c5c4b4da4d4f41d.camel@HansenPartnership.com/
> +
> +    Example::
> +
> +      type var __free(free_func);
> +      ... // var not used, but, in future someone might add a return here
> +      var = malloc(var_size);
> +      ...
> +
> +    should be initialized as::
> +
> +      ...
> +      type var __free(free_func) = malloc(var_size);
> +      ...
> +
>  
>  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,