On Tue, Jul 27, 2021 at 01:57:56PM -0700, Kees Cook wrote:
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 no meaningful object code changes (i.e. only source line number induced differences and optimizations.)
Signed-off-by: Kees Cook keescook@chromium.org
Reviewed-by: Gustavo A. R. Silva gustavoars@kernel.org
Thanks -- Gustavo
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 f19190820e63..b4032e9b130e 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -800,11 +800,10 @@ 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 */ @@ -920,8 +919,8 @@ 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 fc7942c0dddc..5f29c65507e0 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -987,12 +987,10 @@ 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) { @@ -1004,14 +1002,12 @@ 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.
*/ new->queue_mapping = old->queue_mapping;
- It is not yet because we do not want to have a 16 bit hole
- 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