All available gso_type flags are currently in use, so
extend gso_type from 'unsigned short' to 'unsigned int'
to be able to add further flags.
We reorder the struct skb_shared_info to use
two bytes of the four byte hole before dataref.
All fields before dataref are cleared, i.e.
four bytes more than before the change.
The remaining two byte hole is moved to the
beginning of the structure, this protects us
from immediate overwites on out of bound writes
to the sk_buff head.
Structure layout on x86-64 before the change:
struct skb_shared_info {
unsigned char nr_frags; /* 0 1 */
__u8 tx_flags; /* 1 1 */
short unsigned int gso_size; /* 2 2 */
short unsigned int gso_segs; /* 4 2 */
short unsigned int gso_type; /* 6 2 */
struct sk_buff * frag_list; /* 8 8 */
struct skb_shared_hwtstamps hwtstamps; /* 16 8 */
u32 tskey; /* 24 4 */
__be32 ip6_frag_id; /* 28 4 */
atomic_t dataref; /* 32 4 */
/* XXX 4 bytes hole, try to pack */
void * destructor_arg; /* 40 8 */
skb_frag_t frags[17]; /* 48 272 */
/* --- cacheline 5 boundary (320 bytes) --- */
/* size: 320, cachelines: 5, members: 12 */
/* sum members: 316, holes: 1, sum holes: 4 */
};
Structure layout on x86-64 after the change:
struct skb_shared_info {
short unsigned int _unused; /* 0 2 */
unsigned char nr_frags; /* 2 1 */
__u8 tx_flags; /* 3 1 */
short unsigned int gso_size; /* 4 2 */
short unsigned int gso_segs; /* 6 2 */
struct sk_buff * frag_list; /* 8 8 */
struct skb_shared_hwtstamps hwtstamps; /* 16 8 */
unsigned int gso_type; /* 24 4 */
u32 tskey; /* 28 4 */
__be32 ip6_frag_id; /* 32 4 */
atomic_t dataref; /* 36 4 */
void * destructor_arg; /* 40 8 */
skb_frag_t frags[17]; /* 48 272 */
/* --- cacheline 5 boundary (320 bytes) --- */
/* size: 320, cachelines: 5, members: 13 */
};
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
7f564528a4