From: "Gustavo A. R. Silva" gustavoars@kernel.org
[ Upstream commit c4d49196ceec80e30e8d981410d73331b49b7850 ]
commit d61491a51f7e ("net/sched: cls_u32: Replace one-element array with flexible-array member") incorrecly replaced an instance of `sizeof(*tp_c)` with `struct_size(tp_c, hlist->ht, 1)`. This results in a an over-allocation of 8 bytes.
This change is wrong because `hlist` in `struct tc_u_common` is a pointer:
net/sched/cls_u32.c: struct tc_u_common { struct tc_u_hnode __rcu *hlist; void *ptr; int refcnt; struct idr handle_idr; struct hlist_node hnode; long knodes; };
So, the use of `struct_size()` makes no sense: we don't need to allocate any extra space for a flexible-array member. `sizeof(*tp_c)` is just fine.
So, `struct_size(tp_c, hlist->ht, 1)` translates to:
sizeof(*tp_c) + sizeof(tp_c->hlist->ht) == sizeof(struct tc_u_common) + sizeof(struct tc_u_knode *) == 144 + 8 == 0x98 (byes) ^^^ | unnecessary extra allocation size
$ pahole -C tc_u_common net/sched/cls_u32.o struct tc_u_common { struct tc_u_hnode * hlist; /* 0 8 */ void * ptr; /* 8 8 */ int refcnt; /* 16 4 */
/* XXX 4 bytes hole, try to pack */
struct idr handle_idr; /* 24 96 */ /* --- cacheline 1 boundary (64 bytes) was 56 bytes ago --- */ struct hlist_node hnode; /* 120 16 */ /* --- cacheline 2 boundary (128 bytes) was 8 bytes ago --- */ long int knodes; /* 136 8 */
/* size: 144, cachelines: 3, members: 6 */ /* sum members: 140, holes: 1, sum holes: 4 */ /* last cacheline: 16 bytes */ };
And with `sizeof(*tp_c)`, we have:
sizeof(*tp_c) == sizeof(struct tc_u_common) == 144 == 0x90 (bytes)
which is the correct and original allocation size.
Fix this issue by replacing `struct_size(tp_c, hlist->ht, 1)` with `sizeof(*tp_c)`, and avoid allocating 8 too many bytes.
The following difference in binary output is expected and reflects the desired change:
| net/sched/cls_u32.o | @@ -6148,7 +6148,7 @@ | include/linux/slab.h:599 | 2cf5: mov 0x0(%rip),%rdi # 2cfc <u32_init+0xfc> | 2cf8: R_X86_64_PC32 kmalloc_caches+0xc |- 2cfc: mov $0x98,%edx |+ 2cfc: mov $0x90,%edx
Reported-by: Alejandro Colomar alx@kernel.org Closes: https://lore.kernel.org/lkml/09b4a2ce-da74-3a19-6961-67883f634d98@kernel.org... Signed-off-by: Gustavo A. R. Silva gustavoars@kernel.org Acked-by: Jamal Hadi Salim jhs@mojatatu.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/sched/cls_u32.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c index da4c179a4d418..6663e971a13e7 100644 --- a/net/sched/cls_u32.c +++ b/net/sched/cls_u32.c @@ -366,7 +366,7 @@ static int u32_init(struct tcf_proto *tp) idr_init(&root_ht->handle_idr);
if (tp_c == NULL) { - tp_c = kzalloc(struct_size(tp_c, hlist->ht, 1), GFP_KERNEL); + tp_c = kzalloc(sizeof(*tp_c), GFP_KERNEL); if (tp_c == NULL) { kfree(root_ht); return -ENOBUFS;