While testing for places where zero-sized destinations were still
showing up in the kernel, sock_copy() was found, which is 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]
---
net/core/sock.c | 5 +++--
1 file changed, 3 insertions(+), 2 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;
--
2.34.1
From: Kees Cook <[email protected]>
Date: Fri, 16 Feb 2024 12:44:24 -0800
> While testing for places where zero-sized destinations were still
> showing up in the kernel, sock_copy() was found, which is 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]>
I confirmed unsafe_memcpy() is just memcpy() without fortified checks.
Reviewed-by: Kuniyuki Iwashima <[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]
> ---
> net/core/sock.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 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;
> --
> 2.34.1