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