[PATCH] RDMA/siw: Replace one-element array and use struct_size() helper

[PATCH] RDMA/siw: Replace one-element array and use struct_size() helper

[Gustavo A. R. Silva]

The current codebase makes use of one-element arrays in the following
form:

struct something {
    int length;
    u8 data[1];
};

struct something *instance;

instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
instance->length = size;
memcpy(instance->data, source, size);

but the preferred mechanism to declare variable-length types such as
these ones is a flexible array member[1][2], introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on. So, replace
the one-element array with a flexible-array member.

Also, make use of the new struct_size() helper to properly calculate the
size of struct siw_pbl.

This issue was found with the help of Coccinelle and, audited and fixed
_manually_.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/infiniband/sw/siw/siw.h     | 2 +-
 drivers/infiniband/sw/siw/siw_mem.c | 5 +----
 2 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/infiniband/sw/siw/siw.h b/drivers/infiniband/sw/siw/siw.h
index af5e9f8c0fcd0..5a58a1cc7a7e8 100644
--- a/drivers/infiniband/sw/siw/siw.h
+++ b/drivers/infiniband/sw/siw/siw.h
@@ -139,7 +139,7 @@ struct siw_pble {
 struct siw_pbl {
 	unsigned int num_buf;
 	unsigned int max_buf;
-	struct siw_pble pbe[1];
+	struct siw_pble pbe[];
 };
 
 /*
diff --git a/drivers/infiniband/sw/siw/siw_mem.c b/drivers/infiniband/sw/siw/siw_mem.c
index e2061dc0b043c..87117781d6374 100644
--- a/drivers/infiniband/sw/siw/siw_mem.c
+++ b/drivers/infiniband/sw/siw/siw_mem.c
@@ -349,14 +349,11 @@ dma_addr_t siw_pbl_get_buffer(struct siw_pbl *pbl, u64 off, int *len, int *idx)
 struct siw_pbl *siw_pbl_alloc(u32 num_buf)
 {
 	struct siw_pbl *pbl;
-	int buf_size = sizeof(*pbl);
 
 	if (num_buf == 0)
 		return ERR_PTR(-EINVAL);
 
-	buf_size += ((num_buf - 1) * sizeof(struct siw_pble));
-
-	pbl = kzalloc(buf_size, GFP_KERNEL);
+	pbl = kzalloc(struct_size(pbl, pbe, num_buf), GFP_KERNEL);
 	if (!pbl)
 		return ERR_PTR(-ENOMEM);
 
-- 
2.26.2

Re: [PATCH] RDMA/siw: Replace one-element array and use struct_size() helper

[Jason Gunthorpe]

On Tue, May 19, 2020 at 06:30:18PM -0500, Gustavo A. R. Silva wrote:
> The current codebase makes use of one-element arrays in the following
> form:
> 
> struct something {
>     int length;
>     u8 data[1];
> };
> 
> struct something *instance;
> 
> instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
> instance->length = size;
> memcpy(instance->data, source, size);
> 
> but the preferred mechanism to declare variable-length types such as
> these ones is a flexible array member[1][2], introduced in C99:
> 
> struct foo {
>         int stuff;
>         struct boo array[];
> };
> 
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> inadvertently introduced[3] to the codebase from now on. So, replace
> the one-element array with a flexible-array member.
> 
> Also, make use of the new struct_size() helper to properly calculate the
> size of struct siw_pbl.
> 
> This issue was found with the help of Coccinelle and, audited and fixed
> _manually_.
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
>  drivers/infiniband/sw/siw/siw.h     | 2 +-
>  drivers/infiniband/sw/siw/siw_mem.c | 5 +----
>  2 files changed, 2 insertions(+), 5 deletions(-)

Applied to for-next, thanks

Jason

Re: [PATCH] RDMA/siw: Replace one-element array and use struct_size() helper

[Gustavo A. R. Silva]

On Tue, May 19, 2020 at 08:52:31PM -0300, Jason Gunthorpe wrote:
> > 
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> > ---
> >  drivers/infiniband/sw/siw/siw.h     | 2 +-
> >  drivers/infiniband/sw/siw/siw_mem.c | 5 +----
> >  2 files changed, 2 insertions(+), 5 deletions(-)
> 
> Applied to for-next, thanks
> 

Thanks, Jason.

--
Gustavo