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
