linux-kernel - [PATCH v2] livepatch: Reorder to use before freeing a pointer

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Date:   Sat, 19 Mar 2022 18:51:43 -0700
From:   trix@...hat.com
To:     jpoimboe@...hat.com, jikos@...nel.org, mbenes@...e.cz,
        pmladek@...e.com, joe.lawrence@...hat.com, nathan@...nel.org,
        ndesaulniers@...gle.com
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, Tom Rix <trix@...hat.com>
Subject: [PATCH v2] livepatch: Reorder to use before freeing a pointer

From: Tom Rix <trix@...hat.com>

Clang static analysis reports this issue
livepatch-shadow-fix1.c:113:2: warning: Use of
  memory after it is freed
  pr_info("%s: dummy @ %p, prevented leak @ %p\n",
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The pointer is freed in the previous statement.
Reorder the pr_info to report before the free.

Similar issue in livepatch-shadow-fix2.c

Signed-off-by: Tom Rix <trix@...hat.com>
---
v2: Fix similar issue in livepatch-shadow-fix2.c

 samples/livepatch/livepatch-shadow-fix1.c | 2 +-
 samples/livepatch/livepatch-shadow-fix2.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
index 918ce17b43fda..6701641bf12d4 100644
--- a/samples/livepatch/livepatch-shadow-fix1.c
+++ b/samples/livepatch/livepatch-shadow-fix1.c
@@ -109,9 +109,9 @@ static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
 	void *d = obj;
 	int **shadow_leak = shadow_data;
 
-	kfree(*shadow_leak);
 	pr_info("%s: dummy @ %p, prevented leak @ %p\n",
 			 __func__, d, *shadow_leak);
+	kfree(*shadow_leak);
 }
 
 static void livepatch_fix1_dummy_free(struct dummy *d)
diff --git a/samples/livepatch/livepatch-shadow-fix2.c b/samples/livepatch/livepatch-shadow-fix2.c
index 29fe5cd420472..361046a4f10cf 100644
--- a/samples/livepatch/livepatch-shadow-fix2.c
+++ b/samples/livepatch/livepatch-shadow-fix2.c
@@ -61,9 +61,9 @@ static void livepatch_fix2_dummy_leak_dtor(void *obj, void *shadow_data)
 	void *d = obj;
 	int **shadow_leak = shadow_data;
 
-	kfree(*shadow_leak);
 	pr_info("%s: dummy @ %p, prevented leak @ %p\n",
 			 __func__, d, *shadow_leak);
+	kfree(*shadow_leak);
 }
 
 static void livepatch_fix2_dummy_free(struct dummy *d)
-- 
2.26.3