[PATCH v2] net: sched: cls_u32: Fix allocation size in u32_init()
From: Gustavo A. R. Silva
Date: Wed Oct 04 2023 - 09:19:48 EST
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@xxxxxxxxxx>
Closes: https://lore.kernel.org/lkml/09b4a2ce-da74-3a19-6961-67883f634d98@xxxxxxxxxx/
Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
---
Changes in v2:
- Update subject line.
- Update changelog text.
v1:
- Link: https://lore.kernel.org/linux-hardening/ZN5DvRyq6JNz20l1@work/
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 da4c179a4d41..6663e971a13e 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;
--
2.34.1