While testing for places where zero-sized destinations were still showing
up in the kernel, sock_copy() and inet_reqsk_clone() were found, which
are using very specific memcpy() offsets for both avoiding a portion of
struct sock, and copying beyond the end of it (since struct sock is really
just a common header before the protocol-specific allocation). Instead
of trying to unravel this historical lack of container_of(), just switch
to unsafe_memcpy(), since that's effectively what was happening already
(memcpy() wasn't checking 0-sized destinations while the code base was
being converted away from fake flexible arrays).
Avoid the following false positive warning with future changes to
CONFIG_FORTIFY_SOURCE:
memcpy: detected field-spanning write (size 3068) of destination "&nsk->__sk_common.skc_dontcopy_end" at net/core/sock.c:2057 (size 0)
Signed-off-by: Kees Cook <[email protected]>
---
Cc: Jakub Kicinski <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Paolo Abeni <[email protected]>
Cc: [email protected]
v2- add inet_reqsk_clone() instance too
v1- https://lore.kernel.org/lkml/[email protected]/
---
net/core/sock.c | 5 +++--
net/ipv4/inet_connection_sock.c | 5 +++--
2 files changed, 6 insertions(+), 4 deletions(-)
diff --git a/net/core/sock.c b/net/core/sock.c
index 0a7f46c37f0c..b7ea358eb18f 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2053,8 +2053,9 @@ static void sock_copy(struct sock *nsk, const struct sock *osk)
memcpy(nsk, osk, offsetof(struct sock, sk_dontcopy_begin));
- memcpy(&nsk->sk_dontcopy_end, &osk->sk_dontcopy_end,
- prot->obj_size - offsetof(struct sock, sk_dontcopy_end));
+ unsafe_memcpy(&nsk->sk_dontcopy_end, &osk->sk_dontcopy_end,
+ prot->obj_size - offsetof(struct sock, sk_dontcopy_end),
+ /* alloc is larger than struct, see sk_prot_alloc() */);
#ifdef CONFIG_SECURITY_NETWORK
nsk->sk_security = sptr;
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 459af1f89739..4a1d96ba3ad1 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -906,8 +906,9 @@ static struct request_sock *inet_reqsk_clone(struct request_sock *req,
memcpy(nreq_sk, req_sk,
offsetof(struct sock, sk_dontcopy_begin));
- memcpy(&nreq_sk->sk_dontcopy_end, &req_sk->sk_dontcopy_end,
- req->rsk_ops->obj_size - offsetof(struct sock, sk_dontcopy_end));
+ unsafe_memcpy(&nreq_sk->sk_dontcopy_end, &req_sk->sk_dontcopy_end,
+ req->rsk_ops->obj_size - offsetof(struct sock, sk_dontcopy_end),
+ /* alloc is larger than struct, see sk_prot_alloc() */);
sk_node_init(&nreq_sk->sk_node);
nreq_sk->sk_tx_queue_mapping = req_sk->sk_tx_queue_mapping;
--
2.34.1
From: Kees Cook <[email protected]>
Date: Fri, 16 Feb 2024 15:22:23 -0800
> While testing for places where zero-sized destinations were still showing
> up in the kernel, sock_copy() and inet_reqsk_clone() were found, which
> are using very specific memcpy() offsets for both avoiding a portion of
> struct sock, and copying beyond the end of it (since struct sock is really
> just a common header before the protocol-specific allocation). Instead
> of trying to unravel this historical lack of container_of(), just switch
> to unsafe_memcpy(), since that's effectively what was happening already
> (memcpy() wasn't checking 0-sized destinations while the code base was
> being converted away from fake flexible arrays).
>
> Avoid the following false positive warning with future changes to
> CONFIG_FORTIFY_SOURCE:
>
> memcpy: detected field-spanning write (size 3068) of destination "&nsk->__sk_common.skc_dontcopy_end" at net/core/sock.c:2057 (size 0)
>
> Signed-off-by: Kees Cook <[email protected]>
> ---
> Cc: Jakub Kicinski <[email protected]>
> Cc: "David S. Miller" <[email protected]>
> Cc: Eric Dumazet <[email protected]>
> Cc: Paolo Abeni <[email protected]>
> Cc: [email protected]
>
> v2- add inet_reqsk_clone() instance too
> v1- https://lore.kernel.org/lkml/[email protected]/
> ---
> net/core/sock.c | 5 +++--
> net/ipv4/inet_connection_sock.c | 5 +++--
> 2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 0a7f46c37f0c..b7ea358eb18f 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -2053,8 +2053,9 @@ static void sock_copy(struct sock *nsk, const struct sock *osk)
>
> memcpy(nsk, osk, offsetof(struct sock, sk_dontcopy_begin));
>
> - memcpy(&nsk->sk_dontcopy_end, &osk->sk_dontcopy_end,
> - prot->obj_size - offsetof(struct sock, sk_dontcopy_end));
> + unsafe_memcpy(&nsk->sk_dontcopy_end, &osk->sk_dontcopy_end,
> + prot->obj_size - offsetof(struct sock, sk_dontcopy_end),
> + /* alloc is larger than struct, see sk_prot_alloc() */);
>
> #ifdef CONFIG_SECURITY_NETWORK
> nsk->sk_security = sptr;
> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> index 459af1f89739..4a1d96ba3ad1 100644
> --- a/net/ipv4/inet_connection_sock.c
> +++ b/net/ipv4/inet_connection_sock.c
> @@ -906,8 +906,9 @@ static struct request_sock *inet_reqsk_clone(struct request_sock *req,
>
> memcpy(nreq_sk, req_sk,
> offsetof(struct sock, sk_dontcopy_begin));
> - memcpy(&nreq_sk->sk_dontcopy_end, &req_sk->sk_dontcopy_end,
> - req->rsk_ops->obj_size - offsetof(struct sock, sk_dontcopy_end));
> + unsafe_memcpy(&nreq_sk->sk_dontcopy_end, &req_sk->sk_dontcopy_end,
> + req->rsk_ops->obj_size - offsetof(struct sock, sk_dontcopy_end),
> + /* alloc is larger than struct, see sk_prot_alloc() */);
nit: reqsk is allocated in inet_reqsk_clone().
>
> sk_node_init(&nreq_sk->sk_node);
> nreq_sk->sk_tx_queue_mapping = req_sk->sk_tx_queue_mapping;
> --
> 2.34.1
>