| Message ID | 20200928153052.GA17317@embeddedor |
|---|---|
| State | Accepted |
| Delegated to: | David Miller |
| Headers | show |
| Series | [next] net/sched: cls_u32: Replace one-element array with flexible-array member | expand |
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.
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) {
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(-)