* [PATCH][next] net/sched: cls_u32: Replace one-element array with flexible-array member
@ 2020-09-28 15:30 Gustavo A. R. Silva
2020-09-29 1:48 ` David Miller
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-09-28 15:30 UTC (permalink / raw)
To: Jamal Hadi Salim, Cong Wang, Jiri Pirko, David S. Miller, Jakub Kicinski
Cc: netdev, linux-kernel, Gustavo A. R. Silva, Kees Cook
There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].
Refactor the code according to the use of a flexible-array member in
struct tc_u_hnode and use the struct_size() helper to calculate the
size for the allocations. Commit 5778d39d070b ("net_sched: fix struct
tc_u_hnode layout in u32") makes it clear that the code is expected to
dynamically allocate divisor + 1 entries for ->ht[] in tc_uhnode. Also,
based on other observations, as the piece of code below:
1232 for (h = 0; h <= ht->divisor; h++) {
1233 for (n = rtnl_dereference(ht->ht[h]);
1234 n;
1235 n = rtnl_dereference(n->next)) {
1236 if (tc_skip_hw(n->flags))
1237 continue;
1238
1239 err = u32_reoffload_knode(tp, n, add, cb,
1240 cb_priv, extack);
1241 if (err)
1242 return err;
1243 }
1244 }
we can assume that, in general, the code is actually expecting to allocate
that extra space for the one-element array in tc_uhnode, everytime it
allocates memory for instances of tc_uhnode or tc_u_common structures.
That's the reason for passing '1' as the last argument for struct_size()
in the allocation for _root_ht_ and _tp_c_, and 'divisor + 1' in the
allocation code for _ht_.
[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.9-rc1/process/deprecated.html#zero-length-and-one-element-arrays
Tested-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/5f7062af.z3T9tn9yIPv6h5Ny%25lkp@intel.com/
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
net/sched/cls_u32.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 7b69ab1993ba..54209a18d7fe 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -79,7 +79,7 @@ struct tc_u_hnode {
/* The 'ht' field MUST be the last field in structure to allow for
* more entries allocated at end of structure.
*/
- struct tc_u_knode __rcu *ht[1];
+ struct tc_u_knode __rcu *ht[];
};
struct tc_u_common {
@@ -353,7 +353,7 @@ static int u32_init(struct tcf_proto *tp)
void *key = tc_u_common_ptr(tp);
struct tc_u_common *tp_c = tc_u_common_find(key);
- root_ht = kzalloc(sizeof(*root_ht), GFP_KERNEL);
+ root_ht = kzalloc(struct_size(root_ht, ht, 1), GFP_KERNEL);
if (root_ht == NULL)
return -ENOBUFS;
@@ -364,7 +364,7 @@ static int u32_init(struct tcf_proto *tp)
idr_init(&root_ht->handle_idr);
if (tp_c == NULL) {
- tp_c = kzalloc(sizeof(*tp_c), GFP_KERNEL);
+ tp_c = kzalloc(struct_size(tp_c, hlist->ht, 1), GFP_KERNEL);
if (tp_c == NULL) {
kfree(root_ht);
return -ENOBUFS;
@@ -933,7 +933,7 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
NL_SET_ERR_MSG_MOD(extack, "Divisor can only be used on a hash table");
return -EINVAL;
}
- ht = kzalloc(sizeof(*ht) + divisor*sizeof(void *), GFP_KERNEL);
+ ht = kzalloc(struct_size(ht, ht, divisor + 1), GFP_KERNEL);
if (ht == NULL)
return -ENOBUFS;
if (handle == 0) {
--
2.27.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH][next] net/sched: cls_u32: Replace one-element array with flexible-array member
2020-09-28 15:30 [PATCH][next] net/sched: cls_u32: Replace one-element array with flexible-array member Gustavo A. R. Silva
@ 2020-09-29 1:48 ` David Miller
0 siblings, 0 replies; 2+ messages in thread
From: David Miller @ 2020-09-29 1:48 UTC (permalink / raw)
To: gustavoars
Cc: jhs, xiyou.wangcong, jiri, kuba, netdev, linux-kernel, keescook
From: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Date: Mon, 28 Sep 2020 10:30:52 -0500
> There is a regular need in the kernel to provide a way to declare having
> a dynamically sized set of trailing elements in a structure. Kernel code
> should always use “flexible array members”[1] for these cases. The older
> style of one-element or zero-length arrays should no longer be used[2].
>
> Refactor the code according to the use of a flexible-array member in
> struct tc_u_hnode and use the struct_size() helper to calculate the
> size for the allocations. Commit 5778d39d070b ("net_sched: fix struct
> tc_u_hnode layout in u32") makes it clear that the code is expected to
> dynamically allocate divisor + 1 entries for ->ht[] in tc_uhnode. Also,
> based on other observations, as the piece of code below:
>
> 1232 for (h = 0; h <= ht->divisor; h++) {
> 1233 for (n = rtnl_dereference(ht->ht[h]);
> 1234 n;
> 1235 n = rtnl_dereference(n->next)) {
> 1236 if (tc_skip_hw(n->flags))
> 1237 continue;
> 1238
> 1239 err = u32_reoffload_knode(tp, n, add, cb,
> 1240 cb_priv, extack);
> 1241 if (err)
> 1242 return err;
> 1243 }
> 1244 }
>
> we can assume that, in general, the code is actually expecting to allocate
> that extra space for the one-element array in tc_uhnode, everytime it
> allocates memory for instances of tc_uhnode or tc_u_common structures.
> That's the reason for passing '1' as the last argument for struct_size()
> in the allocation for _root_ht_ and _tp_c_, and 'divisor + 1' in the
> allocation code for _ht_.
>
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] https://www.kernel.org/doc/html/v5.9-rc1/process/deprecated.html#zero-length-and-one-element-arrays
>
> Tested-by: kernel test robot <lkp@intel.com>
> Link: https://lore.kernel.org/lkml/5f7062af.z3T9tn9yIPv6h5Ny%25lkp@intel.com/
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Applied.
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2020-09-29 1:48 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-09-28 15:30 [PATCH][next] net/sched: cls_u32: Replace one-element array with flexible-array member Gustavo A. R. Silva
2020-09-29 1:48 ` David Miller
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).