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 >
