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Message-ID: <ZR1maZoAh2W/0Vw6@work> Date: Wed, 4 Oct 2023 15:19:37 +0200 From: "Gustavo A. R. Silva" <gustavoars@...nel.org> To: Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, "Gustavo A. R. Silva" <gustavoars@...nel.org> Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, "Gustavo A. R. Silva" <gustavoars@...nel.org>, linux-hardening@...r.kernel.org, Kees Cook <keescook@...omium.org> Subject: [PATCH v2] net: sched: cls_u32: Fix allocation size in u32_init() 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@...nel.org> Closes: https://lore.kernel.org/lkml/09b4a2ce-da74-3a19-6961-67883f634d98@kernel.org/ Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org> --- 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
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