[PATCH 1/2] livepatch: handle kzalloc failure

[PATCH 1/2] livepatch: handle kzalloc failure

[Nicholas Mc Guire]

kzalloc() return should always be checked - notably in example code
where this may be seen as reference. On failure of allocation
livepatch_fix1_dummy_alloc() should return NULL.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
---

Problem was 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
(with some unrelated sparse warnings on symbols not being static)

Patch is against 4.20-rc6 (localversion-next is next-20181213)

 samples/livepatch/livepatch-shadow-fix1.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
index 49b1355..a0e8f04 100644
--- a/samples/livepatch/livepatch-shadow-fix1.c
+++ b/samples/livepatch/livepatch-shadow-fix1.c
@@ -89,6 +89,9 @@ struct dummy *livepatch_fix1_dummy_alloc(void)
 	 * pointer to handle resource release.
 	 */
 	leak = kzalloc(sizeof(int), GFP_KERNEL);
+	if (!leak)
+		return NULL;
+
 	klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
 			 shadow_leak_ctor, leak);
 
-- 
2.1.4

[PATCH 2/2] livepatch: handle kzalloc failure

[Nicholas Mc Guire]

kzalloc() return should be checked. On dummy_alloc() failing
in kzalloc() NULL should be returned.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
---

Problem was 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
(with a number of unrelated sparse warnings on symbols not being static)

Patch is against 4.20-rc6 (localversion-next is next-20181213)

 samples/livepatch/livepatch-shadow-mod.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/samples/livepatch/livepatch-shadow-mod.c b/samples/livepatch/livepatch-shadow-mod.c
index 4c54b25..57d5cde 100644
--- a/samples/livepatch/livepatch-shadow-mod.c
+++ b/samples/livepatch/livepatch-shadow-mod.c
@@ -118,6 +118,8 @@ noinline struct dummy *dummy_alloc(void)
 
 	/* Oops, forgot to save leak! */
 	leak = kzalloc(sizeof(int), GFP_KERNEL);
+	if (!leak)
+		return NULL;
 
 	pr_info("%s: dummy @ %p, expires @ %lx\n",
 		__func__, d, d->jiffies_expire);
-- 
2.1.4

Re: [PATCH 1/2] livepatch: handle kzalloc failure

[Petr Mladek]

On Thu 2018-12-13 12:09:49, Nicholas Mc Guire wrote:
> kzalloc() return should always be checked - notably in example code
> where this may be seen as reference. On failure of allocation
> livepatch_fix1_dummy_alloc() should return NULL.
> 
> Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
> ---
> 
> Problem was 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
> (with some unrelated sparse warnings on symbols not being static)
> 
> Patch is against 4.20-rc6 (localversion-next is next-20181213)
> 
>  samples/livepatch/livepatch-shadow-fix1.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
> index 49b1355..a0e8f04 100644
> --- a/samples/livepatch/livepatch-shadow-fix1.c
> +++ b/samples/livepatch/livepatch-shadow-fix1.c
> @@ -89,6 +89,9 @@ struct dummy *livepatch_fix1_dummy_alloc(void)
>  	 * pointer to handle resource release.
>  	 */
>  	leak = kzalloc(sizeof(int), GFP_KERNEL);
> +	if (!leak)
> +		return NULL;

It should be:

	if (!leak) {
		kfree(d);
		return NULL;
	}

Note that The check is not strictly needed in this artificial
example because we never read/write any data there. But I agree
that we should add the check to promote the the right programming
patterns.

Best Regards,
Petr

Re: [PATCH 2/2] livepatch: handle kzalloc failure

[Petr Mladek]

On Thu 2018-12-13 12:09:50, Nicholas Mc Guire wrote:
> kzalloc() return should be checked. On dummy_alloc() failing
> in kzalloc() NULL should be returned.
> 
> Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
> ---
> 
> Problem was 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
> (with a number of unrelated sparse warnings on symbols not being static)
> 
> Patch is against 4.20-rc6 (localversion-next is next-20181213)
> 
>  samples/livepatch/livepatch-shadow-mod.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/samples/livepatch/livepatch-shadow-mod.c b/samples/livepatch/livepatch-shadow-mod.c
> index 4c54b25..57d5cde 100644
> --- a/samples/livepatch/livepatch-shadow-mod.c
> +++ b/samples/livepatch/livepatch-shadow-mod.c
> @@ -118,6 +118,8 @@ noinline struct dummy *dummy_alloc(void)
>  
>  	/* Oops, forgot to save leak! */
>  	leak = kzalloc(sizeof(int), GFP_KERNEL);
> +	if (!leak)
> +		return NULL;

The same comments apply here as for PATCH 1/2.

Best Regards,
Petr

Re: [PATCH 1/2] livepatch: handle kzalloc failure

[Nicholas Mc Guire]

On Thu, Dec 13, 2018 at 01:31:39PM +0100, Petr Mladek wrote:
> On Thu 2018-12-13 12:09:49, Nicholas Mc Guire wrote:
> > kzalloc() return should always be checked - notably in example code
> > where this may be seen as reference. On failure of allocation
> > livepatch_fix1_dummy_alloc() should return NULL.
> > 
> > Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
> > ---
> > 
> > Problem was 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
> > (with some unrelated sparse warnings on symbols not being static)
> > 
> > Patch is against 4.20-rc6 (localversion-next is next-20181213)
> > 
> >  samples/livepatch/livepatch-shadow-fix1.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
> > index 49b1355..a0e8f04 100644
> > --- a/samples/livepatch/livepatch-shadow-fix1.c
> > +++ b/samples/livepatch/livepatch-shadow-fix1.c
> > @@ -89,6 +89,9 @@ struct dummy *livepatch_fix1_dummy_alloc(void)
> >  	 * pointer to handle resource release.
> >  	 */
> >  	leak = kzalloc(sizeof(int), GFP_KERNEL);
> > +	if (!leak)
> > +		return NULL;
> 
> It should be:
> 
> 	if (!leak) {
> 		kfree(d);
> 		return NULL;
> 	}
> 
> Note that The check is not strictly needed in this artificial
> example because we never read/write any data there. But I agree
> that we should add the check to promote the the right programming
> patterns.
>
thanks for catching this !
will send a V2.

thx!
hofrat