linux-kernel - [PATCH 2/2] livepatch: check kzalloc return values

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Date:   Fri, 14 Dec 2018 17:56:10 +0100
From:   Nicholas Mc Guire <hofrat@...dl.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Jessica Yu <jeyu@...nel.org>, Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org, Nicholas Mc Guire <hofrat@...dl.org>
Subject: [PATCH 2/2] livepatch: check kzalloc return values

kzalloc() return should always be checked - notably in example code
where this may be seen as reference. On failure of allocation in
livepatch_fix1_dummy_alloc() respectively dummy_alloc() previous
allocation is freed (thanks to Petr Mladek <pmladek@...e.com> for
catching this) and NULL returned.

Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
Fixes: 439e7271dc2b ("livepatch: introduce shadow variable API")
---

Problem located with an experimental coccinelle script

Patch was compile tested with: x86_64_defconfig + FTRACE=y
FUNCTION_TRACER=y, EXPERT=y, LATENCYTOP=y, SAMPLES=y,
SAMPLE_LIVEPATCH=y

Patch is against 4.20-rc6 (localversion-next is next-20181214)
on top of 0001-livepatch-fix-non-static-warnings.patch 

 samples/livepatch/livepatch-shadow-fix1.c | 5 +++++
 samples/livepatch/livepatch-shadow-mod.c  | 4 ++++
 2 files changed, 9 insertions(+)

diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
index eaab10f..1974eb5 100644
--- a/samples/livepatch/livepatch-shadow-fix1.c
+++ b/samples/livepatch/livepatch-shadow-fix1.c
@@ -89,6 +89,11 @@ static __noclone struct dummy *livepatch_fix1_dummy_alloc(void)
 	 * pointer to handle resource release.
 	 */
 	leak = kzalloc(sizeof(int), GFP_KERNEL);
+	if (!leak) {
+		kfree(d);
+		return NULL;
+	}
+
 	klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
 			 shadow_leak_ctor, leak);
 
diff --git a/samples/livepatch/livepatch-shadow-mod.c b/samples/livepatch/livepatch-shadow-mod.c
index dc69da0..b4ece36 100644
--- a/samples/livepatch/livepatch-shadow-mod.c
+++ b/samples/livepatch/livepatch-shadow-mod.c
@@ -123,6 +123,10 @@ static __noclone noinline struct dummy *dummy_alloc(void)
 
 	/* Oops, forgot to save leak! */
 	leak = kzalloc(sizeof(int), GFP_KERNEL);
+	if (!leak) {
+		kfree(d);
+		return NULL;
+	}
 
 	pr_info("%s: dummy @ %p, expires @ %lx\n",
 		__func__, d, d->jiffies_expire);
-- 
2.1.4