Re: [PATCH] mptcp: Use struct_group() to avoid cross-field memset()

From: Mat Martineau
Date: Fri Jan 21 2022 - 15:45:06 EST


On Thu, 20 Jan 2022, Kees Cook wrote:

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally writing across neighboring fields.

Use struct_group() to capture the fields to be reset, so that memset()
can be appropriately bounds-checked by the compiler.

Cc: Mat Martineau <mathew.j.martineau@xxxxxxxxxxxxxxx>
Cc: Matthieu Baerts <matthieu.baerts@xxxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx
Cc: mptcp@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
net/mptcp/protocol.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)


Thanks Kees, looks good to me. I checked around for other MPTCP structs that would need similar attention and didn't see any.

Reviewed-by: Mat Martineau <mathew.j.martineau@xxxxxxxxxxxxxxx>


diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 0e6b42c76ea0..85317ce38e3f 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -408,7 +408,7 @@ DECLARE_PER_CPU(struct mptcp_delegated_action, mptcp_delegated_actions);
struct mptcp_subflow_context {
struct list_head node;/* conn_list of subflows */

- char reset_start[0];
+ struct_group(reset,

unsigned long avg_pacing_rate; /* protected by msk socket lock */
u64 local_key;
@@ -458,7 +458,7 @@ struct mptcp_subflow_context {

long delegated_status;

- char reset_end[0];
+ );

struct list_head delegated_node; /* link into delegated_action, protected by local BH */

@@ -494,7 +494,7 @@ mptcp_subflow_tcp_sock(const struct mptcp_subflow_context *subflow)
static inline void
mptcp_subflow_ctx_reset(struct mptcp_subflow_context *subflow)
{
- memset(subflow->reset_start, 0, subflow->reset_end - subflow->reset_start);
+ memset(&subflow->reset, 0, sizeof(subflow->reset));
subflow->request_mptcp = 1;
}

--
2.30.2



--
Mat Martineau
Intel