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skbuff: Switch structure bounds to struct_group()

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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).

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com> # drivers/net/wireguard/*
Link: https://lore.kernel.org/lkml/20210728035006.GD35706@embeddedor
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Kees Cook 2021-11-20 16:31:49 -08:00 committed by David S. Miller
parent fba84957e2
commit 03f61041c1
3 changed files with 9 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
drivers/net/wireguard/queueing.h
View File

@ -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;

10
include/linux/skbuff.h
View File

@ -811,12 +811,10 @@ 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];
/* public: */
struct_group(headers,
/* private: */
__u8 __pkt_type_offset[0];
@ -921,9 +919,7 @@ struct sk_buff {
u64 kcov_handle;
#endif
/* private: */
__u32 headers_end[0];
/* public: */
); /* end headers group */
/* These elements must be at the end, see alloc_skb() for details. */
sk_buff_data_t tail;

14
net/core/skbuff.c
View File

@ -992,12 +992,10 @@ 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)
{
@ -1009,14 +1007,12 @@ 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);