[PATCH v3] sock: Use unsafe_memcpy() for sock_copy()

[PATCH v3] sock: Use unsafe_memcpy() for sock_copy()

[Kees Cook]

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 <keescook@chromium.org>
---
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: netdev@vger.kernel.org
 v3: fix inet_reqsk_clone() comment
 v2: https://lore.kernel.org/lkml/20240216232220.it.450-kees@kernel.org
 v1: https://lore.kernel.org/lkml/20240216204423.work.066-kees@kernel.org
---
 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..6a14a44aa161 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 above */);
 
 	sk_node_init(&nreq_sk->sk_node);
 	nreq_sk->sk_tx_queue_mapping = req_sk->sk_tx_queue_mapping;
-- 
2.34.1

Re: [PATCH v3] sock: Use unsafe_memcpy() for sock_copy()

[Simon Horman]

On Mon, Mar 04, 2024 at 01:29:31PM -0800, Kees Cook wrote:
> 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 <keescook@chromium.org>
> ---
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: netdev@vger.kernel.org
>  v3: fix inet_reqsk_clone() comment
>  v2: https://lore.kernel.org/lkml/20240216232220.it.450-kees@kernel.org
>  v1: https://lore.kernel.org/lkml/20240216204423.work.066-kees@kernel.org

Reviewed-by: Simon Horman <horms@kernel.org>

Re: [PATCH v3] sock: Use unsafe_memcpy() for sock_copy()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon,  4 Mar 2024 13:29:31 -0800 you wrote:
> 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).
> 
> [...]

Here is the summary with links:
  - [v3] sock: Use unsafe_memcpy() for sock_copy()
    https://git.kernel.org/netdev/net-next/c/ff73f8344e58

You are awesome, thank you!
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