libceph: use struct_size() for kmalloc() in crush_decode()

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

instance = kmalloc(sizeof(struct foo) + count * sizeof(struct boo), GFP_KERNEL);

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL);

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/net/ceph/osdmap.c b/net/ceph/osdmap.c
index 98c0ff3..48a31dc 100644 (file)
--- a/net/ceph/osdmap.c
+++ b/net/ceph/osdmap.c
@@ -495,9 +495,8 @@ static struct crush_map *crush_decode(void *pbyval, void *end)
                          / sizeof(struct crush_rule_step))
                        goto bad;
 #endif
-               r = c->rules[i] = kmalloc(sizeof(*r) +
-                                         yes*sizeof(struct crush_rule_step),
-                                         GFP_NOFS);
+               r = kmalloc(struct_size(r, steps, yes), GFP_NOFS);
+               c->rules[i] = r;
                if (r == NULL)
                        goto badmem;
                dout(" rule %d is at %p\n", i, r);