In preparation for FORTIFY_SOURCE performing compile-time and run-time field bounds checking for memcpy(), memmove(), and memset(), avoid intentionally writing across neighboring fields.
Replace the existing empty member position markers "headers_start" and "headers_end" with a struct_group(). This will allow memcpy() and sizeof() to more easily reason about sizes, and improve readability. "pahole" shows no size nor member offset changes to struct sk_buff. "objdump -d" shows no object code changes (outside of WARNs affected by source line number changes). Cc: "Jason A. Donenfeld" <ja...@zx2c4.com> Cc: "David S. Miller" <da...@davemloft.net> Cc: Jakub Kicinski <k...@kernel.org> Cc: Jonathan Lemon <jonathan.le...@gmail.com> Cc: Alexander Lobakin <aloba...@pm.me> Cc: Jakub Sitnicki <ja...@cloudflare.com> Cc: Marco Elver <el...@google.com> Cc: Willem de Bruijn <will...@google.com> Cc: wireguard@lists.zx2c4.com Cc: net...@vger.kernel.org Signed-off-by: Kees Cook <keesc...@chromium.org> Reviewed-by: Gustavo A. R. Silva <gustavo...@kernel.org> Link: https://lore.kernel.org/lkml/20210728035006.GD35706@embeddedor --- drivers/net/wireguard/queueing.h | 4 +--- include/linux/skbuff.h | 9 ++++----- net/core/skbuff.c | 14 +++++--------- 3 files changed, 10 insertions(+), 17 deletions(-) diff --git a/drivers/net/wireguard/queueing.h b/drivers/net/wireguard/queueing.h index 4ef2944a68bc..52da5e963003 100644 --- a/drivers/net/wireguard/queueing.h +++ b/drivers/net/wireguard/queueing.h @@ -79,9 +79,7 @@ static inline void wg_reset_packet(struct sk_buff *skb, bool encapsulating) u8 sw_hash = skb->sw_hash; u32 hash = skb->hash; skb_scrub_packet(skb, true); - memset(&skb->headers_start, 0, - offsetof(struct sk_buff, headers_end) - - offsetof(struct sk_buff, headers_start)); + memset(&skb->headers, 0, sizeof(skb->headers)); if (encapsulating) { skb->l4_hash = l4_hash; skb->sw_hash = sw_hash; diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 6bdb0db3e825..fee9041aa402 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -801,11 +801,10 @@ struct sk_buff { __u8 active_extensions; #endif - /* fields enclosed in headers_start/headers_end are copied + /* Fields enclosed in headers group are copied * using a single memcpy() in __copy_skb_header() */ - /* private: */ - __u32 headers_start[0]; + struct_group(headers, /* public: */ /* if you move pkt_type around you also must adapt those constants */ @@ -922,8 +921,8 @@ struct sk_buff { u64 kcov_handle; #endif - /* private: */ - __u32 headers_end[0]; + ); /* end headers group */ + /* public: */ /* These elements must be at the end, see alloc_skb() for details. */ diff --git a/net/core/skbuff.c b/net/core/skbuff.c index f9311762cc47..fd5ce57ccce6 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -991,12 +991,10 @@ void napi_consume_skb(struct sk_buff *skb, int budget) } EXPORT_SYMBOL(napi_consume_skb); -/* Make sure a field is enclosed inside headers_start/headers_end section */ +/* Make sure a field is contained by headers group */ #define CHECK_SKB_FIELD(field) \ - BUILD_BUG_ON(offsetof(struct sk_buff, field) < \ - offsetof(struct sk_buff, headers_start)); \ - BUILD_BUG_ON(offsetof(struct sk_buff, field) > \ - offsetof(struct sk_buff, headers_end)); \ + BUILD_BUG_ON(offsetof(struct sk_buff, field) != \ + offsetof(struct sk_buff, headers.field)); \ static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old) { @@ -1008,14 +1006,12 @@ static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old) __skb_ext_copy(new, old); __nf_copy(new, old, false); - /* Note : this field could be in headers_start/headers_end section + /* Note : this field could be in the headers group. * It is not yet because we do not want to have a 16 bit hole */ new->queue_mapping = old->queue_mapping; - memcpy(&new->headers_start, &old->headers_start, - offsetof(struct sk_buff, headers_end) - - offsetof(struct sk_buff, headers_start)); + memcpy(&new->headers, &old->headers, sizeof(new->headers)); CHECK_SKB_FIELD(protocol); CHECK_SKB_FIELD(csum); CHECK_SKB_FIELD(hash); -- 2.30.2
