[PATCH] audit: Use struct_size() helper in alloc_chunk

[PATCH] audit: Use struct_size() helper in alloc_chunk

[Gustavo A. R. Silva]

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:

struct audit_chunk {
	...
        struct node {
                struct list_head list;
                struct audit_tree *owner;
                unsigned index;         /* index; upper bit indicates 'will prune' */
        } owners[];
};

Make use of the struct_size() helper instead of an open-coded version
in order to avoid any potential type mistakes.

So, replace the following form:

offsetof(struct audit_chunk, owners) + count * sizeof(struct node);

with:

struct_size(chunk, owners, count)

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 kernel/audit_tree.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
index e49c912f862d0..1b7a2f0417936 100644
--- a/kernel/audit_tree.c
+++ b/kernel/audit_tree.c
@@ -188,11 +188,9 @@ static struct fsnotify_mark *alloc_mark(void)
 static struct audit_chunk *alloc_chunk(int count)
 {
 	struct audit_chunk *chunk;
-	size_t size;
 	int i;
 
-	size = offsetof(struct audit_chunk, owners) + count * sizeof(struct node);
-	chunk = kzalloc(size, GFP_KERNEL);
+	chunk = kzalloc(struct_size(chunk, owners, count), GFP_KERNEL);
 	if (!chunk)
 		return NULL;
 
-- 
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Re: [PATCH] audit: Use struct_size() helper in alloc_chunk

[Paul Moore]

On Sun, May 24, 2020 at 4:47 PM Gustavo A. R. Silva
<gustavoars@kernel.org> wrote:
> One of the more common cases of allocation size calculations is finding
> the size of a structure that has a zero-sized array at the end, along
> with memory for some number of elements for that array. For example:
>
> struct audit_chunk {
>         ...
>         struct node {
>                 struct list_head list;
>                 struct audit_tree *owner;
>                 unsigned index;         /* index; upper bit indicates 'will prune' */
>         } owners[];
> };
>
> Make use of the struct_size() helper instead of an open-coded version
> in order to avoid any potential type mistakes.
>
> So, replace the following form:
>
> offsetof(struct audit_chunk, owners) + count * sizeof(struct node);
>
> with:
>
> struct_size(chunk, owners, count)
>
> This code was detected with the help of Coccinelle.
>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
>  kernel/audit_tree.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)

Thanks, this looks reasonable to me, but it came in too late for the
v5.8 merge window (I dislike taking changes past -rc5/6 unless
critical).  Once the merge window closes I'll merge this into
audit/next.

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Re: [PATCH] audit: Use struct_size() helper in alloc_chunk

[Gustavo A. R. Silva]

On Mon, Jun 01, 2020 at 11:36:09AM -0400, Paul Moore wrote:
> >
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> > ---
> >  kernel/audit_tree.c | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> Thanks, this looks reasonable to me, but it came in too late for the
> v5.8 merge window (I dislike taking changes past -rc5/6 unless

Sounds sensible.

> critical).  Once the merge window closes I'll merge this into
> audit/next.
> 

Thanks, Paul.
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Re: [PATCH] audit: Use struct_size() helper in alloc_chunk

[Paul Moore]

On Mon, Jun 1, 2020 at 11:36 AM Paul Moore <paul@paul-moore.com> wrote:
> On Sun, May 24, 2020 at 4:47 PM Gustavo A. R. Silva
> <gustavoars@kernel.org> wrote:
> > One of the more common cases of allocation size calculations is finding
> > the size of a structure that has a zero-sized array at the end, along
> > with memory for some number of elements for that array. For example:
> >
> > struct audit_chunk {
> >         ...
> >         struct node {
> >                 struct list_head list;
> >                 struct audit_tree *owner;
> >                 unsigned index;         /* index; upper bit indicates 'will prune' */
> >         } owners[];
> > };
> >
> > Make use of the struct_size() helper instead of an open-coded version
> > in order to avoid any potential type mistakes.
> >
> > So, replace the following form:
> >
> > offsetof(struct audit_chunk, owners) + count * sizeof(struct node);
> >
> > with:
> >
> > struct_size(chunk, owners, count)
> >
> > This code was detected with the help of Coccinelle.
> >
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> > ---
> >  kernel/audit_tree.c | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
>
> Thanks, this looks reasonable to me, but it came in too late for the
> v5.8 merge window (I dislike taking changes past -rc5/6 unless
> critical).  Once the merge window closes I'll merge this into
> audit/next.

FYI, I just merged this into audit/next.  Thanks!

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